MASTER’S THESIS
Universitetstryckeriet, Luleå
2010:022 CIV
Magnus Brännström Jonas Pelli
Patient Transfer
Design and Development of a Ceiling Track Hoist
MASTER OF SCIENCE PROGRAMME Mechanical Engineering
Luleå University of Technology
Department of Applied Physics and Mechanical Engineering Division of Computer Aided Design
2010:022 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 10/022 - - SE
Preface
The work described in this report is the results of a 30 ECTS master thesis work conducted at Luleå University of Technology in collaboration with RoMedic AB. The thesis is the final project for two Master of Science students in mechanical engineering with a specialization in product development.
To make this project possible, we have had great asset from involved personnel at RoMedic AB who has helped us with their great experiences and knowledge base, especially Magnus Holmberg and Malin Wallström. We have also received good support and feedback from our coach at Luleå University of Technology; Magnus Karlberg. We would like to thank them and everyone else involved in the project that made it possible to carry out the thesis work in the best possible way.
To conclude the work at the end of the project, we are more than satisfied with the way it has turned out as well as with the results and feel that we have gained a lot of valuable experiences that will prove helpful in the future. More important though, we have had a great time, met lots of new friends and been given the opportunity to get walloped on the ice hockey rink.
Magnus Brännström Jonas Pelli
Luleå 2010-02-01
Abstract
Providing assistive devices for disabled and elderly people in order to simplify their lives and increase their independence is an important task in today’s care sector.
RoMedic AB is a complete supplier of patient transfer devices but would like to increase their competitiveness on the ceiling track hoist market by the development of a new ceiling track hoist that should be stronger, faster and include more features than existing solutions. The project can be divided into 4 stages; starting with the design space exploration (DSE) stage were the actual needs for all important stakeholders were identified and by various methods translated into requirement specifications. After the DSE stage, the concept design stage were carried out where different concepts were developed and evaluated in order to find the most competitive solution. This led to the detail design stage where the chosen concept was realized and manufacturing specifications for all parts of the system were developed. In the last step, a fully functional, full scale prototype was built, tested and evaluated. Hence, the project resulted in a prototype along with complete CAD data and manufacturing specifications. In comparison to RoMedic AB’s existing comparable ceiling track hoist, the team developed a more powerful hoist which is capable of lifting 25% more at up to a 200% faster lifting speed. This was achieved while keeping the size, weight and cost of the hoist at a similar level as the comparable solution and was possible due to, among other things, the design of a brand new drive train. Beside these performance factors, a number of innovative features have been developed and the project will continue throughout 2010 with further evaluation and development of the hoist, with the goal to release the product to the market in the close future.
Table of contents
1 DEVELOPMENT OF A WORLD LEADING CEILING TRACK HOIST ... 1
2 THEORY ... 3
2.1 PATIENT TRANSFER ... 3
3 DESIGN SPACE EXPLORATION ... 7
3.1 PROJECT INPUT DATA ... 7
3.2 NEEDFINDING ... 8
3.3 BENCHMARKING ... 12
3.4 RELATED TECHNOLOGY ... 17
3.5 REQUIREMENT SPECIFICATIONS ... 19
4 CONCEPT DESIGN ... 23
4.1 CONCEPT GENERATION ... 23
4.2 CONCEPT EVALUATION ... 25
4.3 CONCEPT SELECTION ... 28
5 DETAIL DESIGN ... 31
5.1 ELECTRIC MOTOR ... 31
5.2 POWER TRANSMISSION ... 33
5.3 BRAKE SYSTEM ... 34
5.4 DRIVE TRAIN... 34
5.5 ELECTRIC POWER SUPPLY ... 40
5.6 RAILS ... 43
5.7 LIFT STRAP ... 46
5.8 LIFT STRAP SHAFT ... 47
5.9 LIFT STRAP STEERING SHAFT ... 48
5.10 EMERGENCY BRAKE ... 48
5.11 QUICK WINDING MECHANISM ... 52
5.12 CHASSIS ... 54
5.13 HOIST MANEUVERING ... 57
5.14 SURVEILLANCE, LOGGING AND HOIST CONTROL SYSTEM... 58
5.15 CASING ... 60
6 TESTING ... 61
7 DESIGN SUMMARY ... 63
8 DISCUSSIONS AND CONCLUSIONS ... 65
9 FUTURE WORK ... 67
LIST OF REFERENCES ... 69
APPENDIX A. INTERVIEW GUIDES ...
APPENDIX B. BENCHMARKING STUDY ...
APPENDIX C. RISK ANALYSIS 1 ...
APPENDIX D. CONCEPT GENERATION SUMMERY ...
APPENDIX E. EXPLODED VIEWS AND DRAWINGS ...
APPENDIX F. DATA SHEETS ...
APPENDIX G. GANTT CHART ...
List of tables
TABLE 3.1MISSION STATEMENT ... 7
TABLE 3.2GROUPED AND RATED NEEDS WITH RELATIVE IMPORTANCE FROM +(LOWEST) TO +++ (HIGHEST) ... 9
TABLE 3.3REQUIREMENT SPECIFICATIONS ... 20
TABLE 4.1WEIGHTED CONCEPT SELECTION MATRIX ... 29
TABLE 5.1ESTIMATED COMPONENT COSTS ... 31
TABLE 5.2DRIVE TRAIN COMPONENTS SUMMERY ... 40
TABLE 5.3CONDUCTIVITY FOR DIFFERENT MATERIALS ... 42
TABLE 5.4MAXIMUM DEFLECTION FOR DIFFERENT DISTANCE BETWEEN ATTACHMENTS POINTS .... 45
TABLE 5.5SUMMARY OF DIFFERENT LIFT STRAPS ... 46
TABLE 5.6MOTOR STEERING AND CIRCUIT CARD FUNCTIONALITY LIST ... 58
TABLE 7.1CONCEPT HOIST SPECIFICATION EVALUATION ... 63
List of figures
FIGURE 1.1ROMEDIC AB’S CEILING TRACK HOIST IN USE ... 1FIGURE 2.1TRANSFERRING PRODUCTS IN USE ... 3
FIGURE 2.2POSITIONING PRODUCTS IN USE ... 4
FIGURE 2.3SUPPORT PRODUCTS IN USE ... 4
FIGURE 2.4LIFTING PRODUCTS IN USE ... 5
FIGURE 2.5EXAMPLES HOW THE CEILING TRACK HOIST IS USED TOGETHER WITH RAILS... 5
FIGURE 3.1LIKO AB-LIKORALL 250 ... 13
FIGURE 3.2GULDMANN AB-GH3(13) AND GH2 ... 13
FIGURE 3.3ARJO AB–MAXISKY 1000 ... 14
FIGURE 3.4HUMANCARE AB–ROOMER 5200 ... 14
FIGURE 3.5ETAC AB-NOVA ... 15
FIGURE 3.6INVACARE AB–ROBIN ... 15
FIGURE 3.7TREBO AB-LUNA WITH ITS DIFFERENT INSTALLATIONS ... 16
FIGURE 3.8DIFFERENT CEILING HOISTS CONSTRUCTIONS ... 17
FIGURE 3.9CEILING MOUNTED AND MOBILE ELECTRIC WINCHES ... 18
FIGURE 3.10ROMEDIC AB’S MOBILE LIFT EVA450 ... 18
FIGURE 4.1FIRST BRAINSTORMING SESSION ... 24
FIGURE 4.2BRAINSTORMING ... 24
FIGURE 4.3CONCEPT 1-TRADITIONAL DESIGN ... 26
FIGURE 4.4CONCEPT 2–BUILT INTO RAIL ... 27
FIGURE 4.5CONCEPT 3-AROUND I-BEAM (ONE MOTOR) ... 28
FIGURE 4.6CONCEPT 4-AROUND I-BEAM (TWO MOTORS) ... 28
FIGURE 5.1 A,PERMANENT MAGNET MOTOR B,WINDSHIELD MOTOR C,PANCAKE MOTOR ... 32
FIGURE 5.2DIFFERENT GEAR TYPES ... 33
FIGURE 5.3DIAGRAM OF THE POWER DEMAND FOR DIFFERENT PATIENT WEIGHTS ... 36
FIGURE 5.4SINGLE TIMING BELT 1 ... 38
FIGURE 5.5SINGLE TIMING BELT 2 ... 38
FIGURE 5.6LIFT STRAP SHAFT IN LINE WITH PLANETARY GEAR AND ELECTRIC MOTOR ... 39
FIGURE 5.7DOUBLE TIMING BELTS ... 39
FIGURE 5.8ROMEDIC AB’S 64MM SQUARE ALUMINUM PROFILE ... 43
FIGURE 5.9I-BEAM PROFILE ... 44
FIGURE 5.10FE-ANALYSIS SHOWING MAXIMUM DEFLECTION OF THE I-BEAM WITH A DISTANCE OF 2900MM BETWEEN THE ATTATCHMENTS POINTS ... 45
FIGURE 5.11DIFFERENT TYPES OF LIFT STRAPS. ... 47
FIGURE 5.12 A, LIFT STRAP SHAFT AND LIFT STRAP ... 47
FIGURE 5.13LIFT STRAP STEERING SHAFT ... 48
FIGURE 5.14EMERGENCY BRAKE (A; UNENGAGED AND B; ENGAGED) ... 49
FIGURE 5.16DETAIL OF SPRING SOLUTION IN EMERGENCY BREAK ... 50
FIGURE 5.17MAXIMUM SPRING TORQUE CALCULATIONS ... 51
FIGURE 5.18QUICK WINDING MECHANISM ... 52
FIGURE 5.19CHASSIS IN ALUMINUM ... 55
FIGURE 5.20EXPLODED VIEW OF CEILING TRACK HOIST ... 55
FIGURE 5.21FE-ANALYSIS OF CHASSIS ... 57
FIGURE 7.1CONCEPT HOIST DIMENSIONS ... 64
FIGURE 7.2RENDERED CAD MODEL AND PHYSICAL PROTOTYPE OF THE FINAL CONCEPT;HULK .... 64
Nomenclature
Variable Description Unit
m Mass kg
F Force N
M Torque Nm
P Power W
r Radii m
g Gravitational constant m/s2
ω Angular speed rad/s
v Velocity m/s
R Resistance Ω
ρ Resistivity Ωm
L Length m
A Area m2
U Voltage V
δ Deflection m
E Young’s modulus N/m2
Ic Current A
Ii Second moment of inertia mm4
J Moment of inertia Kgm2
a Acceleration m/s2
α Angular acceleration rad/s2
1
1 Development of a world leading ceiling track hoist
RoMedic AB is a part of the Handicare group which develops and manufactures equipment for increased independence which simplifies the life of disabled and elderly people (1). RoMedic AB is the only complete supplier of assistive devices for patient transfer and their product range is divided into four different areas:
Transfer, positioning, support and lifting (2). The company was established in 1984 when occupational injuries in the care sector were a major problem. At this time the company focused on soft products, such as sliding mats. RoMedic AB grew rapidly after the start and in 2007 they took another step by introducing electro- mechanical lifting devices. One of these hoists is the ceiling track hoist called RISE which is shown in Figure 1.1 (2).
Figure 1.1 RoMedic AB’s ceiling track hoist in use
Today the ceiling track hoist market is the fastest growing one in the care sector (3). RoMedic AB do however not own the design of the ceiling track hoist RISE which is bought from a competitor, something which makes it more expensive and more difficult to improve. RoMedic AB’s vision is to be world leading on the ceiling track hoist market and therefore need to develop an own, more competitive hoist.
Therefore, the project described in this report was initiated, with the goal to develop a new concept hoist that better meets the customer needs than existing
2
solutions. To do this the hoist needs to be more user friendly, smaller, less expensive, more aesthetically appealing, have better functionality and contain fewer components than solutions available on the market today. In order to succeed with the project it also needs to fit into RoMedic AB’s product range and profile. The objective for this project is to develop and manufacture a functional, full scale prototype with corresponding drawings and specifications of a new ceiling track hoist that meets the customer’s requirements better than existing solutions.
The hoist will be tested and evaluated and, if the results are satisfactory, the product will be launched on the market around the end of 2010.
3
2 Theory
This theory chapter focuses on lifting techniques, safety and how the care sector works. A common problem in the care sector is heavy lifting, incorrect working techniques and stress (4). To avoid and decrease these situations, assistive devices for the care-industry is developed and manufactured. The aim with the assistive devices is to give the patient an active rehabilitating and a safe transfer from one point to another. Simultaneously they must be designed to facilitate the care giver’s work, providing safety for everyone involved. In order to avoid overstressed personnel and to activate still functional muscles of the patients, it is important to use the correct muscle groups for each unique lift.
2.1 Patient transfer
Assistive devices for patient transfer is a global market and it is growing all the time (2). RoMedic AB has developed a wide product range in order to fulfill all the customer’s needs and the products can be divided into four categories:
transferring, positioning, support and lifting.
2.1.1 Transferring
Transferring products are devices which provide help for the patient when transferring between two points, such as from a wheelchair to the bed or from the toilet to a wheelchair (5). The transferring method depends on the patient situation and can therefore be divided into two subgroups; laying and sitting transfers.
Examples of transferring products and their areas of use are shown in Figure 2.1 (5).
Figure 2.1 Transferring products in use 2.1.2 Positioning
Products related to the positioning category helps to improve and adjust the patient’s position; such as turning in bed, getting further back in a chair or positioning higher up in bed (6). Repositioning of a patient is usually done from
4
sitting or laying and are therefore divided into these two subgroups. Examples of positioning products and their areas of use are illustrated in Figure 2.2 (6).
Figure 2.2 Positioning products in use 2.1.3 Support
This category includes patient uprising and supporting, which provide help when mobilizing from sitting to standing or from lying to sitting position (7). Products in this category also functions in gait training with a patient or when doing standing transfers. Examples of support products and their areas of use are shown in Figure 2.3 (7).
Figure 2.3 Support products in use 2.1.4 Lifting
Lifts can be conducted either manually by hand power or aided by a mechanical lift, usually a mobile lift running on wheels on the floor or a ceiling track hoist. The mechanical solution is always to prefer in lifting situations since it is a better option both for the patient and for the care giver (8). Manual lifts are only used when other options are excluded. Examples of lifting scenarios and their areas of use are shown in Figure 2.4 (8).
5
Figure 2.4 Lifting products in use
A ceiling track hoist is an overhead electric motor controlled by a hand control to raise and lower the patient and it is the most space saving solution available. By rails in the ceiling, patients can be transferred between different areas of the room such as shown in Figure 2.5 (2). To move the patient vertically, the patient is placed in a sling that is raised by the hoist, making the transfer comfortable and ergonomic both for the care giver and for the patient. To transfer the patient the personnel can either use manual power or a motor driven carrier. The motor driven carrier is controlled via a hand control and moves the patient horizontally in the room without any use of muscle power from the care giver. Even though ceiling track hoists are to prefer in most situation they have the drawback, compared to mobile lifts, that their movement is limited to the rail system available in the facility. With good planning this should however not be a problem.
Figure 2.5 Examples how the ceiling track hoist is used together with rails
6
7
3 Design space exploration
As a base for the product development method, the process presented by Ulrich and Eppinger (9) was used. This to achieve a structured process that suited both RoMedic AB’s and Luleå University of Technology’s existing development processes.
In order to properly understand the proposed task and define the problem in a structured way, the design space has to be studied. Initially the different stakeholder’s needs were established and translated into requirement specifications. Parallel to this, a benchmarking survey was conducted where competitive existing products and similar technologies where studied in order to gain inspiration and further define what kind of product was needed on the market. This survey also made clear what solutions are available on the market today and what their pros and cons are.
3.1 Project input data
Some requirements were established by the management before the development team got involved. These are found in Table 3.1 and states that the high end hospital segment is the primary market, while the low- and middle end markets;
home (individual homes) and care (nursing and elderly homes) are the secondary markets. The management team further stated that the hoist should be ceiling mounted in some way, that it should have a motor driven carrier and be rechargeable. Finally, they listed the main stakeholders involved in the project.
Table 3.1 Mission statement
Mission statement: Ceiling track hoist
Product Description A ceiling mounted patient hoist
Key Business Goals ~8% market shares or 5000-10000 sold hoists/year within 3-5 year
Primary Market Hospital Secondary Markets Home
Care
Assumptions Ceiling mounted Motor driven carrier Rechargeable Stakeholders Care givers
8 Patients Service Production Sales
Legal department
3.2 Needfinding
In order to specify suitable requirements for the product to be developed a needfinding phase was carried through. The aim with this phase was to find needs that the people who interact with the product perceives important. In many cases though, the users are not aware of all their needs and often get stuck in old behaviors (9). Therefore it is essential that correct and relevant data are collected.
3.2.1 Gathering raw data
The first step when collecting the data needed was to host interviews with people who come in contact with or have knowledge of ceiling track hoists or similar products. Seven different kinds of stakeholders were identified and interview guides were created for each one (See Appendix A. Interview guides). The selected stakeholders were care givers, patients, service technicians, assemblers, technical developers, sales personnel and occupational therapists. The goal with the interviews was to engage discussions about ceiling track hoists in different perspectives and hence gain valuable information. Typical questions used regarded for example what the interview subject perceived positive or negative about existing lifting products, details they thought were missing etc. as well as general reflections. The team engaged in the discussions with follow-up questions and tried to achieve a relaxed talk on the topic were the interview subject felt relaxed and not afraid to speak his/her mind. The interviews were audio recorded so that the team could go through the data afterwards, take notes and compare them to the notes taken during the interviews. From this interesting customer statements could be extracted.
In correlation with the interviews, existing ceiling track hoists were observed in use by care givers and occupational therapists. This gave an opportunity to see how the users actually interacted with the hoist and look for latent needs and details that the users worked around. The team also maneuvered the hoist themselves as well as took on the role as the patient, something which gave a better understanding of the situation and led to further knowledge about undiscovered needs.
9
As a final step, the team carried through needfinding sessions in about the same way as regular brainstorming sessions (9). The project area was discussed and possible needs that came up were written on a whiteboard. At this time many of the needs had been covered in the earlier stages of the data gathering but some new ones occurred. This work also gave a chance to go through and reflect on the needs already found.
3.2.2 Interpreting data
In order to use the customer statements acquired in the earlier stages they needed to be transformed into needs. The main aspect in this work was to phrase the needs in non quantified terms of how the product should be perceived and avoid stating solutions to problems (9). This was done by discussions within the development team. All collected needs were then grouped so that statements that considered the same area were collected as secondary needs under a main primary need, shown in bold in Table 3.2. The primary needs are of a more general form while the secondary needs go more into details and covers certain sub systems.
Also, at this stage needs that were redundant were eliminated. Finally, all statements, primary and secondary were rated after their relative importance, also decided by discussions. The grouped and rated need statement list is found in Table 3.2.
Table 3.2 Grouped and rated needs with relative importance from + (lowest) to +++
(highest) Need
no.
Imp. Need
1 +++ The hoist is safe to use both for the patient and the care giver 2 +++ The patient cannot fall to the ground
3 +++ The hoist is ergonomic to use
4 +++ The patient does not get stuck in an upraised position 5 +++ The hoist does not move in any way by itself
6 ++ People do not get hit by the sling bar 7 +++ The system can easily be put to a stand still 8 ++ The patient feels safe when using the hoist
9 ++ The hoist movement is smooth through the whole cycle 10 ++ The hoist is quite
11 +++ The hoist is easy to use, both manually and electronically 12 +++ It is easy to understand how the hoist should be used 13 ++ The hoist is easy to handle with little muscle power
10 14 ++ The hoist has a low mass
15 ++ The hoist shows information that helps the user 16 +++ The patient can be rotated in the sling
17 + The patient rotation in the sling has a proper amount of inertia 18 + The hoist is controlled from anywhere in the room
19 ++ Hoist components not needed at a certain moment are not in the way 20 ++ Hoist components are near at hand when needed
21 + The hoist is operated without a hand control
22 + The care giver does not need to climb on something to interact with the hoist
23 ++ It takes little time to prepare/finish the lifting procedure 24 + The hoist is quick to store
25 ++ The hoist moves out of the way automatically when not needed
26 ++ The hoist moves in the right speed (vertical and horizontal) at the right time
27 +++ The hoist functions well in transfer
28 +++ The hoist easily transfers patients from A to B 29 +++ The hoist transfers patients between rooms 30 +++ The hoist easily travels between different rails
31 +++ The hoist is easily moved sideways both manually and electronically 32 ++ The drive cart does not skew in the rail
33 +++ The hoist functions well in vertical lifting 34 +++ The lifting height is good
35 +++ Patients can be lifted from the floor 36 +++ The hoist system has a low total build height 37 ++ The hoist is ready for use when needed 38 ++ The hoist is easy to recharge
39 ++ The hoist recharges quickly
40 +++ The hoist does not run out of battery all of a sudden 41 ++ The battery life is good
42 ++ The hoist recharges itself
43 ++ The hoist automatically turns off when not used 44 + The hoist can be recharged everywhere in the rail 45 ++ The hoist is quick to move between separate rails 46 ++ The hoist can be used in different rail systems
47 ++ The hoist is easily, without tools, moved between different rails 48 + The hoist is easy to remove from the rail and send to service
49 ++ The hoist system has an appealing design which fits with RoMedic AB’s profile
50 ++ The system feels robust 51 ++ The system is compact
11 52 ++ The system is discreet
53 + The system is available in different colors
54 ++ The hoist is comfortable for the patient and the care giver 55 + The hoist is comfortable for very large people
56 +++ The sling can be used in different widths 57 + The hoist shows useful information
58 + Useful information is shown at places where you interact with the hoist, such as the hand control
59 ++ The hoist can be used for different needs
60 ++ The hoist functions with different kinds of disabilities 61 ++ The hoist is available in different lifting capacities 62 + The patient feathers in gait training
63 ++ The sling bar is used for mobile lifts as well as ceiling hoists 64 +++ The hoist is durable
65 +++ The hoist has a long life time 66 +++ The hoist is robust
67 +++ Fragile components do not come in contact with moving parts 68 ++ The lift strap does not wear when rotating and twisting the sling bar 69 ++ The hoist system is easy to install
70 ++ The system is quick to install
71 ++ The system can be installed in different types of rooms 72 ++ The hoist is easy to assemble
73 +++ The hoist is safe to assemble 74 ++ The hoist is quick to assemble 75 + The hoist is assembled in modules
76 + The final assembly is done without special tools 77 + The assembly can be done with little work space
78 ++ There is no need for modifying the parts when assembling 79 + The hoist system has the same dimension on most nuts and bolts 80 +++ The hoist is easy to serve
81 +++ Details that often need to be changed or repaired are easy to replace 82 ++ The casing is easy to remove
83 + The hoist lets you know when service is needed 84 + Hoist software is updated automatically 85 ++ The system logs interesting information
86 + The care givers can perform simple service by themselves 87 ++ The hoist is positioned to the segment “hospital”
88 ++ The hoist can be positioned to different segments by removing or changing certain features
12
89 + The lifting capacity is not unnecessarily high 90 +++ The hoist is affordable for its segment 91 +++ The hoist is cheap to produce 92 ++ The hoist has few unique components
93 +++ The total cost per lift cycle is affordable for its segment 94 ++ The hoist is environmentally friendly
95 ++ The hoist is produced in an ethically responsible way
This list of needs has been used as a foundation for the requirement specifications as well as for the concept design.
3.3 Benchmarking
In order to meet the customers’ needs and expectations, a benchmarking study of the ceiling track hoists on the market was executed. This was done to see what features and specifications that the new concept hoist needs to surpass in order to be more competitive than existing solutions. The objective for this benchmarking was to identify differences between competitors’ solutions and also to verify what patents they own. The team looked for patents relating to various methods of lifting in order to understand what is available today, as well as to gain understanding of how the needs could be solved, using different methods. By identifying competitors and different solutions, a knowledge platform for the concept generation was gained. The team started to list relevant competitors and search specifications about ceiling track hoists by screening the internet. It was found that the amount of information to a large extent differed between the companies and the conclusion from the screening was that all competitors have rather similar solutions when transferring a patient from one point to another.
Based on the interviews from the needfinding and own experiences it can be stated that the design and the size of the hoist has a large impact on the customers, this since it is one of the biggest differences between today’s hoists. Studying pictures from competitors’ homepages was not enough to gain a sufficient understanding regarding size and design so it was decided that the most interesting ones should be looked up physically. Hence, the company Hjälpmedelscenter Väst in Gothenburg was visited. Hjälpmedelscenter Väst is a try-out center where patients, care givers, hospital management etc. can compare different ceiling track hoist systems with each other before deciding on a system. Represented companies have their own area in the facility where hoists and accessories can be independently evaluated. The try-out center gave the opportunity to feel, see and
13
take pictures of the most common ceiling track hoist systems on the market. A brief list of what was available is presented below:
3.3.1 Liko AB
Many customers claims that Likorall (see Figure 3.1 (10)) has a rather old fashioned design which gives poor information to the customer about battery life, patient weight etc (11). Compared to competitors, Likorall is a rather large and heavy hoist but it offers good durability and fulfills the customer’s needs about transferring a patient from one point to another and it can be found on many locations.
Figure 3.1 Liko AB - Likorall 250 3.3.2 Guldmann AB
Guldmann AB has two ceiling track hoist models called GH2 (12) and GH3 (13), which are shown in Figure 3.2 (12). These two models are top of the line on today’s market, both from a design- and a technological perspective. The most significant difference between the models is the lifting capacity where the GH3 can lift 100kg more than the GH2 (see more in Appendix B. Benchmarking study). These are durable hoists with a compact and, by customers perceived, appealing design with a display that shows useful information for the patient and the care giver. A special feature with these hoists is that they charge their batteries regardless of where in the rail they are positioned.
Figure 3.2 Guldmann AB - GH3 (13) and GH2
14 3.3.3 Arjo AB
Arjo AB has a ceiling track hoist designed for heavy persons, up to 455kg, called MaxiSky 1000 (14), shown in Figure 3.3 (14). This model is popular on the U.S market where heavy patients in the care sector are a common problem. MaxiSky 1000 is the only hoist on the market which can transfer patients up to 455kg with only one lifting motor. Competitors instead use two hoists connected in series to reach this lifting capacity. Arjo AB has two other models in their product range with a lower lifting capacity: MaxiSky 660 and MaxiSky 440 which are rather basic models.
Figure 3.3 Arjo AB – MaxiSky 1000 3.3.4 HumanCare AB
HumanCare AB uses a different lifting technique in their model Roomer 5200 than seen in the previous hoists: Instead of a fixed hoist installation in the ceiling they utilize a solution where the whole lifting motor is moving up and down from the ceiling (see Figure 3.4 (15)). The benefit with this feature is that the hoist is more mobile and it can easily be moved from room to room under doorpost to another rail system. The disadvantage is that the patients feel discomfortable about having the hoist in their field of vision and it is also easy for the patient to accidentally hit his/hers head against the hoist. Needs for a fixed installation from customers have led to another model called Singel 5100 Satellit, which HumanCare offers as an alternative solution.
Figure 3.4 HumanCare AB – Roomer 5200
15 3.3.5 Etac AB
Etac AB has a compact and light weight ceiling track hoist called Nova which is shown in Figure 3.5 (16). Customers like the design of it, especially since it is rather small and doesn’t stand out to much, i.e. the customers feel that it blends into the environment. Nova has also got a quick release function for the carrier, meaning that the hoist easily can be moved between different rails.
Figure 3.5 Etac AB - Nova 3.3.6 Invacare AB
Invacare AB utilizes an innovative solution in their ceiling track hoist called Robin:
Robin has two lift straps instead of one which is shown in Figure 3.6 (17). The lift straps moves simultaneously up/down and can therefore replace the sling bar which is necessary when using a hoist with one lift strap, since at least two attachment points are required when transferring a patient in a sling. Another benefit with using two lift straps is that the patient doesn’t have anything hanging in front of his/her face. It does however limit the width of the attachment points in comparison to regular sling bar hoists which can be used with sling bars with different widths.
Figure 3.6 Invacare AB – Robin 3.3.7 Trebo AB
Trebo AB’s hoist model is called Luna and can be used in three different installations. The hoist can be fixedly installed both horizontally and vertically in the ceiling or used in a mobile way as HumanCare Roomer 5200, where the whole hoist comes down from the ceiling. The different applications are shown in Figure 3.7
16
(18). The horizontally fixed installation (shown to the far left in Figure 3.7) is the most common in which Luna has a low built height and an appealing design.
Figure 3.7 Trebo AB - Luna with its different installations
By visiting the try-out center, knowledge about ceiling track hoist solutions that are available on the market today and what different features they have were gained.
It can be stated that most hoists are based on the same technology where batteries power an electric motor which in turn, through a gear box, rolls up a lift strap which lifts the patient up and down. The main features separating the hoists are the size and the design. It can further be stated that many of today's hoists do not show interesting information such as battery life, service, patient weight etc. on a display for users and the ones who do gets a positive customer response.
3.3.8 Technology study
To gain a deeper understanding about the technology used in today’s ceiling track hoists, the team decided to disassembly some different brands and models. Four different models were investigated in detail. All the models examined were driven by 2 x 12V batteries that provide an electric motor with power so that it can run a lifting strap which moves the patient up and down. Between the electric motor and the lift strap is some kind of gearbox which gears the torque up so that it will be strong enough to lift patients of around 200-300kg. The mechanics of the studied ceiling hoists are shown in Figure 3.8. One difference between the brands is how they have solved the security features and the assembly of components. The fall protection (the brake that prevents the patient from falling to the ground if something unexpected happens), if it is present, differs between different models.
Some brands use some kind of mechanical solution which slows down the falling patient. Others use dual electric motors in which at least one motor can slow down the lift by using its own inhibition. This works since the probability that both electric motors would fail simultaneously is highly unlikely. Increasing the safety factor to more than eight times on critical details is also a sufficient fall protection according to ISO 10535:2007 (19).
17
Figure 3.8 Different ceiling hoists constructions
3.4 Related technology
In order to gain inspiration for the concept design and not get stuck in existing solutions, other technologies than the ceiling track hoist´s were studied. First, different kinds of lifting equipment were listed in the following areas:
Winches
Mobile patient lifts Elevators
Excavators
Manual assistive equipment
In these areas, manufacturers and retailers were investigated; looking for data sheets, pictures, drawings, patents etc. which resulted in an inspiration library that could be used in the upcoming concept design. Winches, especially electrical ones, are rather similar to ceiling hoists and provide a good source of ideas. They are usually stronger than an average patient hoist but if the components are scaled down it could offer interesting solutions to certain sub systems such as the electric motor, the winding system etc. Two examples of electric winches, one ceiling mounted and one mobile, are shown in Figure 3.9 (20) (21).
18
Figure 3.9 Ceiling mounted and mobile electric winches
Mobile patient lifts has a lot in common with ceiling hoists since they both perform similar tasks, using different techniques. There are a wide variety of manufacturers and many of them also develop ceiling hoist systems. RoMedic AB has a range of different mobile lifts and one of these lifts, EVA450, is shown in Figure 3.10 (2). It was discovered that a mobile patient lifts is more difficult to work with than a ceiling track hoist and the transfer of a patient horizontally takes far more muscle power to perform. The study gave knowledge about the importance of having a new ceiling track hoist that can replace the mobile lift in as many situations as possible.
Figure 3.10 RoMedic AB’s mobile lift EVA450
Manual assistive equipments were also studied and used to gaining knowledge and inspiration. Different kinds of equipments in this field are discussed in more detail in chapter 2, Theory. Finally, to prepare for the upcoming design stages, inspiration for likely sub systems were also considered and brief overviews of different types of rails, gears, electric motors, batteries etc. were conducted. This was done to give the team an overall knowledge of what was available on the market. The outcome of this is presented in chapter 5, Detail design.
19
3.5 Requirement specifications
The needs extracted in the previous stages are highly subjective and in most cases it is difficult to correctly evaluate how different products fulfill them. The first step when creating the requirement specifications was therefore to establish a list of measurable metrics (9). This was done within the development team by discussing how different needs could correspond to different numerically measurable statements and resulted in about 40 different metrics that either had numerical-, or binary values. To establish these values, two aspects were considered: Which market segment the product would be positioned in and how competitive products performed under respective metric. Since the primary market, according to the mission statement, is the high end hospital segment, the concept that was to be developed had to have top performance levels in most specification posts.
To find the comparative performance of competitive products, a benchmarking study was conducted. This study included the eight largest ceiling hoist suppliers with a number of hoists each. Available, published data for each hoist was studied and as many details from the requirement specifications as possible were noted.
This was then compiled into a benchmarking table covering the performance of competitive products (see Appendix B. Benchmarking study).
When quantifying the previously described metrics it was important to understand that the different posts influence each other. If, for example, the amount of lift cycles on one charge is increased it is likely that the charge time also will be increased since a bigger battery probably will be needed. This means that it is difficult to achieve top ratings for all metrics and that tradeoffs almost always needs to be considered when setting the specifications. Because of this and to avoid narrowing the design space to much, two columns were added to the requirement specifications; one with marginal values that were acceptable and one with ideal values that were set as goals. Both these values were set by comparing the benchmarked material collected for competitive products with each other and with RoMedic AB’s existing solutions. It was then decided within the development team how the new concept should perform relative to this information and numeric values were set. The final requirement specifications, including all metrics, their corresponding need statements, their relative importance rating (1 is lowest, 3 is highest), the marginal and the ideal values can be found in Table 3.3.
20
Table 3.3 Requirement specifications Metric
nr.
Need nr.
Metric Imp. Units Marginal
value
Ideal value
1 1 Overload protection 3 Binary Y Y
2 1, 2 Mechanical safety factor 3 nr 2 2
3 1, 2 Lift strap safety factor 3 nr 6-10 6
4 2 Strap emergency brake 3 Binary N Y
5 4 Electrical/manual emergency lowering
3 Binary E E/M
6 7 Emergency stop 3 Binary Y Y
7 10 Noise level 2 dB <50 <35
8 14 Total mass 2 Kg <9 <8
9 15, 57 The interface shows battery life, patient weight and time
2 Binary Y,N,N Y,Y,Y
10 16 Patient rotation 3 Binary Y Y
11 23, 24 Time to prepare for lifting (excl. sling)
1 s <30 <10
12 26 Unloaded lifting speed 2 cm/s 10-15 15-20
13 26 Loaded lifting speed 2 cm/s 4-5 6-7
14 26 Motor driven carrier speed 2 cm/s 25-30 30-35 15 34,
36, 51
Min. build height (between rail and sling mounting points)
3 cm <30 <20
16 34, 35 Lift interval 3 cm 200-260 220-250
17 39 Charge time 2 hrs <4 <2
18 40 Prevent drained battery 3 Text Shut
down
Always charging 19 41 Lift cycles on one charge (85
kg)
2 nr >80 >130
20 43 Automatic shut down 2 Binary Y Y
21 46 Adjustable carrier wheel base/height
2 Binary N Y
22 47 Time to move hoist between rails
2 s <60 <30
23 51, 52 Hoist casing length 2 cm <30 <20
24 51, 52 Hoist casing width 2 cm <20 <15
25 51, 52 Hoist casing height (rail to casing bottom)
2 cm <15 <10
26 55, 56 Sling mounting points width interval
2 cm 350-600 300-650
27 59, 61 Lifting capacity 3 kg 250-300 250-400
21
28 64, 65 Number of cycles in life time 3 nr >11 000 >15 000
29 64 IP class 2 nr 20 43
30 64 ISO 10535- / 12182 (and other relevant directives) approved
2 Binary Y Y
31 64 Duty cycle 2 nr 10/90 20/80
32 72, 74 Assemble time 2 hrs <2 <1
33 80, 81 Battery change time 2 min <2 <0,5
34 80, 81 Lift strap change time 2 min <10 <5 35 80, 81 Circuit board change time 1 min <5 <3
36 80, 82 Casing remove time 2 min <1 <0,2
37 85 The system logs cycles, charges, on/off, uptime, power, changed components
2 Binary N,N,Y, Y,Y,N
Y,Y,Y, Y,Y,Y
38 88 Add-ons: Lamp, scale, internet connection etc.
2 Binary N,N,N Y,Y,Y 39 90,
91, 92
Unit production cost (2000 hoists/year)
3 sek <2 500 <1 800 40 94, 95 Passes all environmental
and ethical requirements
3 Binary Y Y
It should be noted that the high end hospital segment, set as the primary market for the new design, has high demands on robustness, durability and innovative, relevant features. This means that the requirement specifications as well as the list of needs are formed to fit this segment. I should also be noted that a competitive ceiling track hoist for this segment also will fulfill most demands of the secondary markets. There are mainly two aspects of the hoist that need to be altered to do this completely: First of all the price need to be kept low enough, something which might require a downgraded version of the hospital hoist. Secondly, there are other demands on the design, e.g. a smaller hoist that blends well into a home environment might be necessary.
22
23
4 Concept design
The objective of this project was to develop an innovative solution to the proposed task. To achieve this, a throughout and structured concept design process was carried out. Before this stage was entered however, a risk analysis regarding the whole project was conducted in order to identify the largest risks and find ways to avoid them. This analysis is found in Appendix C. Risk analysis 1.
4.1 Concept generation
To succeed with the concept design of a project it is important to perform the initial concept generation with an open mind, keeping the design space wide. This was a major point in the first steps of the concept generation which consisted of two sessions, focused on ceiling track hoists in general. The first session was carried out by the development team itself and it started out by brainstorming about words, sketches, descriptions, wishes etc. The brainstorming sessions concerned ideas from desired features regarding the hoist to minor details or brief ideas of a whole lifting system. The ideas were written or drawn on post-its which were presented to the other half of the team and then posted on the wall. After some time, the generated ideas were screened and notes that concerned the same areas were grouped and given a group name. The discovered groups of interest were:
Lift strap Sling bar Design
Hoist maneuvering Weightlessness Electric power supply Power transmission
Noise reduction Safety
Build-in Service
Mounting: Rail – Hoist Desired attributes Accessories
After the grouping activity, new brainstorming sessions were carried through, now focusing on one group at a time. This strategy gave the possibility to focus on a specific sub system and by lots of discussions come up with new ideas, some of them are shown in Figure 4.1.
24
Figure 4.1 First brainstorming session
In the next stage of the concept generation process, another brainstorming session was held in which more detailed ideas were drawn on A3 papers. At this stage, new ideas were considered but a lot of work regarded the different ideas already generated i.e. developing them into more detailed ones. This was the last step of the first concept generation session which ended by documenting and storing the work for the upcoming evaluation. Before this though, a second session was held, following the same steps described in this chapter. This time the brainstorming group consisted of the development team, the head of technical development at RoMedic AB, a graphical designer from RoMedic AB and an external technical product development consultant. No material from the first session was presented here since the main aim was to extract ideas and feedback from people not directly involved in the development process. A summary of the generated ideas from both these sessions can be found in Appendix B. Benchmarking study and two snapshots from the sessions are shown in Figure 4.2.
Figure 4.2 Brainstorming
At this stage no ideas were discarded and instead every idea, post-it and paper was kept and served as the foundation for the concept evaluation phase that followed.
25
4.2 Concept evaluation
In order to summarize all ideas from the brainstorming session, the team attached all post-its on A3 papers under its associated title created in the previous stage, discarding ideas similar to each other. This was done in order to organize the material and get a better overview of the ideas that had been generated. To extract the most interesting ideas from the created groups and their corresponding post- its, the team created new concept headlines for what was thought to be the most interesting and innovative areas of ideas and hence worth putting extra focus on.
This led to the following list:
Patient appear weightless Hoist built into rail Hoist built around rail Hoist built around I-beam Double lift straps
Electric motor inside lift strap shaft
Traditional solution1 with alternative components Magnet coupling to ceiling
Direct drive (no gearbox) Motor on end of the rail Components built into sling bar
To find the best solution and to ensure that nothing from the brainstorming is missed it is important to think widely and therefore the concept headlines were held rather general. The team continued with a summary of the generated ideas, looking for different solutions to the created headlines which resulted in the identification of 17 different concepts. Each of these were sketched again, now in more detail, to show its specific functionality and technical solution. It was quickly discovered that some of these 17 concepts were similar or solved the same problem, something which resulted in the merging of them. Concepts that were considered to have a too long development time, be too technically complex or have a too high manufacturing cost were sorted out, something which narrowed the number of concepts down to eight. These eight concepts corresponded to the most important needs discovered in the needfinding stage, i.e. the need for better and faster maneuverability, higher lift height and a more aesthetically appealing
1The ceiling track hoist hangs below the rail and the lift strap is driven by an electric motor supplied by batteries.
26
design with less “hospital feeling”. The concepts were evaluated by discussions within the development team and with the head of technical development at RoMedic AB. Also, at this stage a multi-voting session with staff from technical development, marketing, production and administration was held. All this resulted in the decision to proceed with the evaluation for four of the concepts, all being described below.
4.2.1 Concept 1 - Traditional design
This traditional solution is based on the same idea as the most common ceiling track hoists today. The hoist is hanging below the rail connected to a carrier that runs inside the rail, as schematically illustrated in Figure 4.3. The set of components in concept 1 with a belt-driven electric motor and a planetary gearbox will, compared to competitors, decrease the built height from the ceiling to the bottom of the hoist casing, the width and the length. Concept 1 is a traditional solution which the customers are accustomed to. The main drawbacks with the concept are that the hoist will, compare to other concepts, be rather large and not very innovative.
Figure 4.3 Concept 1 - Traditional design 4.2.2 Concept 2 - Build into rail
In order to meet the demands of an almost invisible ceiling track hoist, concept 2, with the lift built inside the rail, was developed (see Figure 4.4). This solution, with a planetary gearbox inline with the electric motor, will decrease the built height from the ceiling to the bottom of the hoist. A decreased built height does however lead to an increased hoists length which makes it more difficult to perform lifts near walls and do cornering. An alternative version of concept 2 is that the hoist is placed under the rail with a carrier inside the rail like a traditional solution, making it usable in competitors’ rail systems. In order to fit the hoist into the rail, a bigger rail than usually must be used, something which may cause the general impression
27
regarding the size of the hoist system to be negative, even though the hoist itself is concealed. Compared to other concepts, this one will have a lower lifting capacity and be more difficult to perform service on.
Figure 4.4 Concept 2 – Built into rail 4.2.3 Concept 3 - Around I-beam (one motor)
Using an I-beam as a rail makes the use of available space more efficient than what is the case with the traditional rail solution. This since components can be positioned around and under the rail, something which leads to a decreased total build height (illustrated in Figure 4.5). This concept has one electric motor with a belt-driven planetary gearbox. The hoist can also, together with an external drive cart, be placed below a traditional rail and hence be used in competitors’ rail systems. A separate drive cart and casing must however be developed in order to make it feasible. The stiffness/mass ratio of the rail can be increased by using an I- beam which makes it less expensive to produce and easier to install. The main difficulty with this concept is to make it run in curves without locking itself because of its length. However, compared to concept 2, this will be easier to solve since the components are placed beside the rail instead of on the inside. Another difficulty is that the casing may need some sort of moving parts which follows the rail when cornering. There might also be a problem when the new rail system is introduced since the market is conservative and not very receptive of new ideas.
28
Figure 4.5 Concept 3 - Around I-beam (one motor) 4.2.4 Concept 4 - Around I-beam (two motors)
This concept is similar to concept 3 with the difference that it includes two electric motors (see Figure 4.6) instead of one. This provides the possibility to offer two different hoist models: One with a lower lifting capacity, using one electric motor and another with a higher lifting capacity, using two electric motors. This decreases the production cost since a smaller electric motor can be used for the most common, high volume hoist for patient weights up to 250kg.
Figure 4.6 Concept 4 - Around I-beam (two motors)
4.3 Concept selection
To objectively evaluate the final concepts, a weighted Pugh’s matrix was created.
This matrix was designed to contain the most important criteria’s discovered in the needfinding and to evaluate the concepts with RoMedic AB’s current comparable ceiling track hoist; Rise, as a reference. The rating for each criteria was established between 1 (worst) and 5 (best) where RoMedic AB’s Rise had an index rating of 2.5 for each criteria. The ratings for each concept was multiplied with the weight of each criterion (in parentheses) and then summarized, resulting in the total weighted rating shown in Table 4.1.
29
Table 4.1 Weighted concept selection matrix
Concept 1
Traditional design
Concept 2 Built into
rail
Concept 3 Around I-beam
(one motor)
Concept 4 Around I-beam
(two motors)
Reference RoMedic
Rise Size/appearance
(0.8)
3 4,5 4 4 2,5
Build height (0.8)
3 5 4,5 4,5 2,5
Price (0.7)
2,5 3,5 3 2,5 2,5
Ease of installation (0.4)
2,5 2,5 4 4 2,5
Ease of service (0.6)
2,5 1 2 2 2,5
Move between rails (0.6)
4,5 3,5 3,5 3,5 2,5
Sound level (0.9)
4 4 4 4 2,5
Fits in different rails (0.7)
5 1 1 1 2,5
Degree of innovation (0.8)
3 5 4,5 4,5 2,5
Ease of use (1.0)
4 4 4 4 2,5
Life time (0.7)
2,5 4 3 2,5 2,5
Lifting capacity (0.9)
4 3 4 5 2,5
Mass (0.7)
2,5 3,5 3 3,5 2,5
Complexity (0.6)
4 1,5 2 2 2,5
Total weighted rating
33,25 34,6 34,4 34,95 24,75
Ranking 4 2 3 1 5
These final concepts along with the results from the Pugh’s matrix were presented to the president of RoMedic AB and the heads of sales, technical product development and administration. In this meeting it was agreed upon, as shown in the matrix, that Concept 4 is the most competitive solution. Three drawbacks compared to Concept 1 were however identified: First of all it requires that the customer invests not only in a new hoist, but in a whole new rail system. This makes the solution more difficult to sell, especially to customers that already have a rail system installed. Secondly, many customers in the health aid industry are very conservative and may request a traditional design that travels under a rectangular profile rail. Finally, Concept 4 requires a longer development time than Concept 1
30
since a whole new rail system also needs to be developed. This led to the decision to combine Concept 1 and 4 and create two versions of the hoist. One version functions as Concept 4 and travels in the I-beam profile as previously described. In the other version, the hoist is mounted under an external drive cart that can travel in any rail and hence function as a traditional solution. This second version is thought to be completed first and preferably released on the market in the end of 2010. The development team will however focus on the I-beam solution when entering the detail design since it requires special functionalities concerning component layout, chassis, cornering etc. When all this is ready, a casing and a drive cart can be designed and then the traditional version of the hoist can be released on the market. This gives more time to develop the new rail system and then release the I-beam version along with the new rail system in mid 2011.
Furthermore, the hoist will be designed with two different lifting capacities of 200- 250kg and 350-400kg, achieved at 6-10cm/s. This will be achieved by developing two editions of each version with one or two electric motors.
31
5 Detail design
Each sub system was evaluated by using different parameters that are described under respective chapter. The cost, specified at a maximum of 2500sek, is a major factor for each sub system and in order to not exceed the budget, each sub system cost should preferably not be higher than what is estimated in Table 5.1. This estimation enabled the possibility to quickly reduce the number of unfeasible solutions of each sub system. It should be noted however that the prices the development team can obtain usually are a lot higher than what the sales department are able to achieve when taking in proper quotes.
Table 5.1 Estimated component costs
Detail Estimated cost (sek)
Drive train (Electric motor, power transmission and brake) 1000
Batteries 90
Transformer 400
Circuit card 350
Quick winding mechanism 70
Lift strap 40
Drive cart 100
Emergency brake 100
Chassis 110
Casing 40
Hand control 200
Total 2500
Each sub system has, if nothing else is stated, been designed with a maximum load safety factor of two. Exploded views and drawings (manufactured components) are shown in Appendix E. Exploded views and drawings while datasheets for purchased components are shown in Appendix F. Data sheets.
5.1 Electric motor
A prerequisite for the project was that an electric motor should be used. Since the motor, along with the power transmission, is the single most important part of the ceiling track hoist, it was natural to start the detail design by investigating this sub system. One of the main factors that eliminate many different kinds of possible electric motors is the price. Since the established total production cost for the hoist is set to be between 1800sek and 2500sek, calculated at 2000 hoists per year, the cost for the drive train (electric motor, power transmission and brake system) for the same amount of hoists is estimated to not exceed 1000sek. In the beginning of
32
the process, both AC and DC motors were considered, depending on whether the hoist should be battery- or line powered. It was however identified that the hoist would need at least some kind of emergency battery in case of a power outage, something which led to the conclusion that a DC motor was preferable. Three different DC motors were estimated to fulfill the requirement specifications:
Permanent magnet motors (Figure 5.1a) Windshield wiper motors (Figure 5.1b) Pancake motors (Figure 5.1c)
The permanent magnet motor and the windshield wiper motor are rather similar in their design but the permanent magnet motor does offer more power to mass- and dimension ratio but at a higher cost than the windshield wiper motor. The pancake motor offers a lower axial dimension but with a higher radial dimension as a downside compared to a permanent magnet or a windshield wiper motor.
Examples of these three types of motors are shown in Figure 5.1 (22) (23).
Figure 5.1 a, Permanent magnet motor b, Windshield motor c, Pancake motor The electric motor should have a mass less than 4kg and be as small as possible. It should also, after the power transmission, provide 50-100Nm at 30-60rpm.
Calculations regarding this are found in chapter 5.4, Drive train. The hoist should be enabled for continuous usage in the lower power range and intermittent usage at maximum load situations. The drive cycle in these situations will be set between 10/90 and 20/80, with the motor running for a maximum of three minutes at a time, meaning that after these three minutes the hoist cannot be used for 12-27 minutes, depending on the chosen drive cycle. What is chosen depends on the results from the testing and evaluation. Different specific electric motors considered are discussed further in chapter 5.4, Drive train.
a b c
