IN
DEGREE PROJECT TECHNOLOGY, FIRST CYCLE, 15 CREDITS
,
STOCKHOLM SWEDEN 2018
Motorized tensioner system
for prosthetic hands
FELIX HARDELL
JONAS TJOMSLAND
FELIX HARDELL JONAS TJOMSLAND
Bachelor’s Thesis at ITM Supervisor: Nihad Subasic
Abstract
Modern research in prosthetic devices and other assis-tive technologies are constantly pushing boundaries. While the technology is impressive, it is still inaccessible for the greater part of the people in need of it. Advanced devices are often extremely expensive and require regularly main-tenance from professionals. Enabling the Future is a global network of volunteers and was founded to face these prob-lems. They design and 3D-print mechanical prosthetics for people in need all over the world.
Most of the designs used by Enabling the Future are purely mechanical and do not implement motors. The purpose of this thesis was to take a new approach to the design and construction of low-cost motorized prosthetic hands. By distancing all the electronic components from the hand, including the motor, the project aimed to create a device compatible with all current designs of the Enabling the Fu-ture community.
To conceptualize this approach a demonstrator was con-structed and tested. It utilized a muscle sensor which al-lowed users to control the hand by tightening their mus-cles. The distance between the electronic components and the prosthetic hand measured approximately one and a half meters and still transfered enough force, from the motor to the hand, to deliver an adequate grip strength.
Keywords
Modern forskning inom protestillverkning och andra handikapphjälpmedel gör kontinuerligt stora framsteg. Trots att tekniken är imponerade är den fortfarande otillgänglig för den största del människor som behöver den. Avancera-de hjälpmeAvancera-del är ofta extremt dyra och kräver kontinuer-ligt underhåll från yrkesverksamma. Enabling the Future, ett globalt nätverk av volontärer, grundades för att utma-na dessa problem. De konstruerar och tillverkar 3D-skrivutma-na mekaniska proteser för människor med behov över hela värl-den.
De flesta konstruktioner som används av Enabling the Fu-ture är helt mekaniska och använder inga motorer. Syftet med detta kandidatexamensarbete var att med nya tillvä-gagångssätt konstruera en billig motoriserad handprotes. Genom att placera all elektronik på en distans från han-den, inklusive motorn själv, var tanken att skapa ett system som är kompatibelt med de konstruktioner som Enabling the Future använder.
För att förverkliga detta konstruerades en prototyp som testats. Prototypen använde sig av en muskelsensor som lät användaren kontrollera proteshanden genom att spän-na sin arm. Distansen mellan de elektriska komponenterspän-na och protesen var ungefär en och en halv meter, samtidigt som tillräckligt stor kraft kunde transporteras för att stänga handen med ett tillräckligt grepp.
Nyckelord
Acknowledgements
First we would like to thank the KTH staff. Specifically, our supervisor Nihad Subasic for all lectures, support and feedback and the lab assistants for answering questions. We would also like to thank Staffan Qvarnström and Tomas Östberg for components as well as ideas about the construction.
Secondly, we would like to thank our fellow KTH students. This includes, the mechatronic master students one year ahead of us, for all their help, and all our friends in the same year who gave us feedback during the seminars and elsewhere. Finally, we would like to thank the e-NABLE community for its existence. All support provided by this community to people without financial possibilities in need of prosthetic devices is invaluable.
EMG Electromyography
e-NABLE Enabling the Future DC Direct Current
GAR Spiral-bound galvanized PLA Polylactic Acid
PM Permanent Magnet
PWM Pulse With Modulation SEK Swedish Kronor
STR Stainless-steel strands
List of Figures
1.1 An early sketch of how the tensioner system could be constructed, drawn on reMarkable. . . 3 2.1 Simple explanation of the whippletree mechanism, drawn on reMarkable. 4 2.2 Illustration of a brushed motor, drawn on reMarkable. . . 6 2.3 Schematic diagram of an H-bridge in two different states, drawn in
Keynote. . . 7 3.1 Sketch of control box, drawn on reMarkable. . . 10 3.2 Schematic diagram of all electronic components, drawn in Keynote. . . 11 3.3 A software flowchart explaining the setup and main loop of the system,
created in Keynote. . . 13 4.1 Time from when the human test subject started closing their hand until
1 Introduction 1 1.1 Background . . . 1 1.2 Purpose . . . 2 1.3 Scope . . . 2 1.4 Method . . . 2 2 Theory 4 2.1 Prosthetic hand . . . 4 2.2 Whippletree . . . 4 2.3 Bowden cable . . . 5 2.4 EMG-sensor . . . 5 2.5 Electric motor . . . 5 2.5.1 Brushed PM DC motor . . . 6 2.5.2 H-bridge . . . 7 3 Demonstrator 8 3.1 Problem formulation . . . 8 3.2 Mechanics . . . 8 3.2.1 Prosthetic hand . . . 8 3.2.2 Whippletree . . . 8
3.2.3 Cable house mounting . . . 9
3.2.4 Wire clamp grip . . . 9
4.1 Conducted experiments . . . 14 4.2 Results . . . 15
5 Discussion and conclusion 16
5.1 Discussion . . . 16 5.2 Conclusions . . . 17
6 Recommendations and future work 18
Bibliography 20
Appendices 21
A Arduino Code 22
B Flexy Hand 2 26
C Redesign of Flexy Hand 2 arm part 27
D Finger configuration of whippletree 28
E Compression spring 29
F Price list of all components 30
G Motor datasheet 31
H Micro switch datasheet 34
I EMG-sensor datasheet 36
Introduction
1.1
Background
In 2011, the World Health Organization estimated that close to 30 million people in developing countries were in need of some kind of prosthetic device [1]. Many of these are victims of conflicts or deceases not present in more developed countries. Low income in combination with inadequate health services increases the magnitude of the problem. Furthermore, people in other parts of the world are facing similar challenges. In the US, nearly two million people are living with limb loss [2]. Even with better welfare and financial conditions, the problem is severe.
Additionally, not only is the demand for an initial prosthetic device increasing, but every recipient needs several replacements and repairs during a lifetime. A rough estimate concludes that every 6-12 months for children and every 3-5 years for adults, a replacement is necessary [3]. It is therefore not surprising that a tra-ditional middle-class family may be unable to afford prosthetic devices when the price range for a prosthetic arm is 3,000 to 30,000 US Dollars (USD) [4].
CHAPTER 1. INTRODUCTION
1.2
Purpose
The purpose of this project was to challenge the traditional approaches used when creating myoelectric prosthetic devices. To demonstrate this, the objective was to produce a working prototype with cheap and easily accessible components, possible to build by the amateur maker.
The following research questions were investigated:
• Can a replaceable and mobile myoelectric system be built to transfer motion from a distant motor to a prosthetic hand?
• Can such a system be built with cheap and easily accessible components?
1.3
Scope
Due to limitations in time and budget, some restrictions were applied to this project. There was a given budget of 1000 Swedish Kronor (SEK) from KTH Royal Institute of Technology on top of components and parts supplied by the machine construction department itself. While this was a relatively small budget it was also a reasonable amount to ensure that the projects solution could be available to everyone. Fur-thermore, a mechatronic implementation was at focus so little consideration was taken to solid mechanics, manufacturing and design.
In order to limit the workload and keep the project within the time constraint, pre-fabricated solutions were prioritized over "Do it yourself" methods. This included the acquired EMG-sensor, the stepper motor driver and the predesigned prosthetic hand.
At the end of the project, the prosthetic hand was required to open and close when the user activated it by muscle contraction. The actuator needed to be able to keep track of its current position thereby controlling the strength of the grip.
1.4
Method
First of all a literature study was conducted. A set of traditional prosthetic construc-tions were researched, including different mechanical, sensor, actuator and manufac-turing techniques. Areas such as soft robotics, haptic technology, electromyography and 3D-printing were investigated.
Figure 1.1. An early sketch of how the tensioner system could be constructed, drawn on reMarkable.
Chapter 2
Theory
2.1
Prosthetic hand
The prosthetic hands developed in the e-NABLE community mainly consist of 3D-printed parts. Each finger has tensile hinges between non-tensile parts in order to operate. To make the prosthetic able to close, artificial tendons from the tip of all fingers are used. The hand closes when the tendons are pulled.
2.2
Whippletree
A whippletree mechanism distributes forces evenly through linkages. On one side loads are applied through wires and on the other side a tension can be applied. In the case of prosthetics, the fingers work as load. If a finger cannot move due to an obstacle, the other fingers will keep on moving which increases the grip of the hand [9]. Since the thumb usually works against the other fingers alone, the force to the thumb should be largest of all fingers. This can be achieved by using different distance relations between different connection in the whippletree, see figure 2.1.
Figure 2.1. Simple explanation of the whippletree mechanism, drawn on
2.3
Bowden cable
A Bowden cable is made of several layers in a specific configuration surrounding a wire. A cable housing with a steel interior and plastic exterior is usually used as outer layer. When the wire is pulled, tension is added to the cable while maintaining a static housing.
In bikes, where Bowden cables are used as shifter cables, Teflon is sometimes used as an extra layer between the wire and the metal interior due to low friction and shifting performance. Furthermore, Teflon does not require lubrication which is otherwise needed. The wire is usually made from spiral-bound galvanized (GAR) or stainless-steel strands (STR). The STR offers greater resistance to corrosion but are usually more expensive than GAR [10].
At the end of the cable there is an end cap which can be configured in different ways. In order to avoid contamination from dirt or water, an open-end cap should be avoided. Instead one option could be sealed end caps with an internal rubber O-ring which keeps the housing clean while offering low friction.
2.4
EMG-sensor
Electromyography (EMG) is the measuring of muscle contractility or the electrical activity in response to nerve stimulation of a muscle [11]. It has traditionally only been used in medical research and diagnosis, however, as a result of the latest developments within embedded systems and integrated systems design the use of EMG has become one of the most common solutions for controlling and steering prosthetic devices. It works, briefly speaking, by measuring the voltage difference between a pair of electrodes placed on a muscle and a third electrode placed at a reference point, preferably a bony part of the users body.
2.5
Electric motor
Electric motors convert electricity into rotation which can be transferred into linear motion by different techniques. Either by using a lead screw as the motor shaft with a nut along the axis or by other solutions such as a bobbin and wire. The maximum amount of torque, MN, a Direct Current (DC) Motor can carry while remaining within its temperature rating is given by
MN = K2ΦN · IN (2.1)
CHAPTER 2. THEORY
on the other hand, is given by
E = K2Φ · ω (2.2)
where E is the counter-electromotive force. [12] 2.5.1 Brushed PM DC motor
A PM DC brush motor can be simply described with four components: stator, ro-tor, brushes and commutaro-tor, see figure 2.2. A magnetic field is generated by the stator containing a permanent magnet. The rotor is made up of windings, which are energized sequentially. When current runs through the windings a magnetic field is produced. The poles of the magnetic field of the windings are attracted to the opposite poles of the magnetic field of the stator.
By carefully switching the direction of the current in the rotor windings it is possible to control the motor. This process, called commutation, is achieved by attaching a commutator on the rotor. When the motor turns, carbon brushes slide over dif-ferent segments of the commutator supplying a charge to that segment. Difdif-ferent segments are connected to different parts of the winding which allows the rotor to continue the turning.
2.5.2 H-bridge
A H-bridge is an electronic circuit that allows current to flow across a load in either direction. This process is controlled by opening and closing switches, see figure 2.3. When the load is a DC motor, one H-bridge is enough in order to run the motor both forward and backwards. In the case of a Bipolar Stepper Motor, which have no center taps on their windings, two H-bridges are necessary to perform the same motion. H-bridges are often integrated into Stepper Motor Drivers [13].
Chapter 3
Demonstrator
3.1
Problem formulation
To validate the functionality and usability of the system, a demonstrator was con-structed. The demonstrator had to be able to transfer force from the motor, through the bowden cable, to the prosthetic hand. On top of this, it had to consist of easily accessible and low-cost components.
3.2
Mechanics
3.2.1 Prosthetic hand
Flexy Hand 2, a design created by Steve Woods [14] and widely used in the e-NABLE community, was chosen for the demonstrator, see Appendix B. All printable parts were printed on an Ultimaker 3D printer. The non-tensile parts in Polylactic Acid (PLA) material and the tensile hinges in a more flexible material called Filaflex. Standard fishing line, capable of carrying a weight of 30 kg, was used as artificial tendons.
The upper part of a Flexy Hand 2, where the tendons are usually fastened, was redesigned for the purpose of this project. By doing this, space for the Whippletree mechanism was allocated and a custom made fastening system for the Bowden cable could be implemented, see Appendix C.
A more detailed description of the assembly process, as well as all printable files for the Flexy Hand, can be found on the e-NABLE website [14].
3.2.2 Whippletree
In this demonstrator only one whippletree was used with the pinky and ring finger connected to the middle finger as one input and the index finger connected to the thumb as the other input. For a more detailed explanation see Appendix D. 3.2.3 Cable house mounting
To mount the cable house in both ends plastic ferrules were attached. This is a so-lution commonly used in bicycles as a conversion between entire housing and single steel wire. The ferrules both repels dirt and restricts the housing from moving in wrong directions.
In the mounting closest to the hand, between the plastic ferrule and the arm part, a compression spring was integrated. This allowed the hand to stay open independent of how the wrist joint was moved, see Appendix E.
3.2.4 Wire clamp grip
In each end of the Bowden cable a wire clamp grip was used. A wire clamp grip created a loop-end of the cable which allowed the fishing line to be easily con-nected. Depending on the placement of the loop-end the entire cable length could be adjusted.
3.2.5 Control box
CHAPTER 3. DEMONSTRATOR
The DC motor and micro switch were placed in the main room of the box. When the motor was working the fishing line was rolled up on a small 3D-printed bobbin. The micro switch told the system when the wire clamp reached the wall, thereby indicated that the hand was fully opened. Two pockets, dimensioned for eight AA batteries, were placed on the outside of the box. The Bowden cable was attached to one of the walls and a small hole allowed the wire to enter the box, see figure 3.1.
3.3
Electronics
3.3.1 Wiring
The demonstrators electronic components were connected as illustrated in figure 3.2.
Figure 3.2. Schematic diagram of all electronic components, drawn in Keynote.
3.3.2 Power supply
CHAPTER 3. DEMONSTRATOR
It should be noted that the batteries supplying both the Arduino and the mo-tor run out before the batteries only supplying the momo-tor run out. Such a solution for the batteries was however considered better than other options, see Chapter 6. 3.3.3 Motor
The DMN29BA-002, a 24V DC brush motor, was chosen as motor for the demon-strator, see Appendix G. The selected model consists of both a DC motor as well as a worm drive. This choice was based on the earlier described restrictions, see Chapter 1, as well as desired torque. To transfer the rotary motion to a linear motion a self-designed bobbin was attached to the D-shaped motor shaft.
3.3.4 Motor driver
STMicroelectronics‚ L298 was deemed to be the best solution for a motor driver. It has a dual H-bridge, able to power two DC motors or one unipolar or bipolar stepper motor. See Appendix J.
Since the demonstrator only consisted of one DC motor, it can be argued that this implementation was unnecessarily complicated. One should, however, know that L298 is cheap, easy-to-use and accessible. In addition to this, it supports stepper motors which can be implemented if the DC motor would break.
3.3.5 EMG-sensor
MyoWare’s muscle Sensor AT-04-001 was chosen because of its low price point to-gether with great usability and out-of-the-box features, see Appendix I.
Since the EMG sensor only reacts to electronic impulses the prosthetic was both opened and closed by the user tightening their muscle. This also made it possible for the user to relax their hand while the prosthetic hand was closed.
3.3.6 Micro switch
To keep track of when the prosthetic hand was entirely open a micro switch, Goobay 10185 from Wentronic, was implemented. See Appendix H. The micro switch was installed where the Bowden cable entered the Control box. When the motor released the fishing line, the hinges retracted the fingers back which closed the micro switch.
3.4
Software
Briefly speaking, the setup process checked and adjusted the position of the hand when the system was turned on. In the main loop, the Arduino read the EMG Sensor’s value and when that reached a predetermined threshold the motor started to pull the wire for a specific length of time. Subsequently, it entered its next stage, constantly reading the EMG value to determine whether to open the hand again. When the value from the EMG sensor yet again reached its threshold, the motor ro-tated in the opposite direction, thus opening the hand. See figure 3.3 for a thorough explanation of the process.
Figure 3.3. A software flowchart explaining the setup and main loop of the system,
Chapter 4
Results
4.1
Conducted experiments
Before assembling the entire demonstrator, experiments were conducted on different module configurations. This was done to reduce the risk of failure in the final prod-uct, by carefully making sure all components were working individually as intended. The first experiment was to investigate how large the force had to be in order to close the prosthetic hand alone completely. To test this, a spring balance was attached to the whippletree connection of the artificial tendons. A spring balance measures in kilograms but can easily be converted into Newtons. The spring bal-ance was pulled until it reached its end position, i.e. the hand was entirely closed, and the weight was measured.
As a continuation of the first experiment, the second experiment aimed for an understanding on how much force the motor was able to transfer through the rest of the tensioner system. In the Bowden cable end, otherwise connected to the whip-pletree, a spring balance was attached. The spring balance was fixed and the motor the motor pulled the wire in the opposite direction. The current was kept at a maximum of 1.2A and with a 24V supply.
4.2
Results
Test Weight [kg]
1 5.5
2 5.4
3 5.5
Table 4.1. Weight to fully close the prosthetic hand alone.
Test Weight [kg]
1 11.5
2 12.0
3 11.7
Table 4.2. Weight possible to transfer through tensioner system from motor.
Figure 4.1. Time from when the human test subject started closing their hand until
Chapter 5
Discussion and conclusion
5.1
Discussion
The force needed to close the hand alone, see Table 4.1, was significantly higher than first expected. This led to several adjustments of the initial construction. Three different motors were tested with gear implementations.
When the final prototype was completed the tensioner system was able to transfer force well above what the hand alone could, see Table 4.2. However, by subtracting the weight the tensioner system could transfer from the weight required to close the prosthetic hand alone, the grip strength was calculated to just over 6 kg.
According to a European study from 2014, the average grip strength among six year old girls was 8.1 kg, while boys in the same age had an average grip strength of 9.1 kg [16]. Since many of the recipients in the e-NABLE community are children, a motorized system delivering 6 kg could be deemed sufficient by users.
Time delays may prove to be a problem, as closing the hand without any load took almost 2.4 seconds on average, see Figure 4.1. This would probably be perceived as very slow for a user in the beginning, until the user becomes accustomed to it. Opening the hand was much faster and probably has a more reasonable time period. There is no doubt that a system which can transfer motion from a distance to a prosthetic hand is possible to create. By using a Bowden cable this can be achieved without keeping the system stretched along one direction. Such a system can be built for less than 1330 SEK, equivalent to 152 USD, as of May 20 2018, see Ap-pendix F.
5.2
Conclusions
A replaceable and mobile myolectric system can be build to transfer motion from a distant motor to a prosthetic hand.
Chapter 6
Recommendations and future work
It is important to once again point out that there were restrictions in this project, making the design options in some cases limited.
As seen in the results, the demonstrator required large torques at reasonable speed in order to operate properly. This, in combination with a low price target, led to problems when choosing the motor. If a motor was too weak, a gear was needed, providing a slow and more complicated system. If a motor with high torque was chosen, the price increased. The noise level from the motor was also taken into consideration. This lead to a compromise between many factors which might have affected the overall performance of the system. A possibility would be to further investigate different motor solutions to implement in the system.
Instead of using 16 AA batteries in series to supply the motor with 24V, other power supply solutions could be interesting to evaluate. Notice that the system needs both enough current and voltage, leading to a high torque as well as rea-sonable rotational speed, see Equation 2.1 and 2.2. One solution is to use other battery types, supporting higher voltage and still offering enough ampere hours. Another solution is a step-up converter, which was actually tested in this construc-tion. A step-up converter offers the possibility to increase the voltage, i.e. speed, by reducing the current, i.e. torque, proportionally. If this is implemented ensure that the step-up conversion is completed before the current enters the H-bridge. It is also important to investigate for how long the power supply might be able to work until the need for charging or changing.
The chosen MyoWare Muscle Sensor was very easy to implement, but in relation to other components rather expensive, see Appendix F. The subsequent costs relat-ing to this component further increase if the electrodes need to be changed often. Muscle sensor implementations that can be removed and reused more easily would be preferred.
The control box used in the demonstrator was from the beginning of the project aimed to fit inside a backpack. Due to time limits such implementation was never tested. A future experiment would be to reduce the entire box size and shape it better for a backpack.
Fishing line has many benefits, it can be rolled up on a bobbin easily and is al-ready widely used as artificial tendons in the e-NABLE community. However, the use of fishing line can result in difficulties in small spaces, such as inside the control box, where knots need to be strong.
3D printing was seen as a good choice since most users in the e-NABLE community have access to this technology. It would be recommended for future projects to continue to create solutions possible to 3D-print.
The Flexy Hand 2 is a popular design which worked well in this project. However, after some testing it was noticed that, the thumb closed faster than the remaining fingers. This led to some difficulties when grabbing different objects. The problem was probably a result of the whippletree configuration but this was never investi-gated further.
Bibliography
[1] WHO. (2011). World report on disability, [Online]. Available: http://www. who . int / disabilities / world _ report / 2011 / report . pdf. (Accessed: 2018.02.13).
[2] Amputee Coalition. (2012). Limb loss statistics, [Online]. Available: https:// www.amputee- coalition.org/limb- loss- resource- center/resourcesfiltered / resources by topic / limb loss statistics / limb loss -statistics/. (Accessed: 2018.02.13).
[3] E. Strait, “Prosthetics in developing countries”, Prosthetic Resident, p. 3, 2006.
[4] G. McGimpsey and T. C. Bradford, “Limb prosthetics services and devices”,
Bioengineering Institute Center for Neuroprosthetics Worcester Polytechnic Institution, 2008.
[5] (2011). Enabling the future, [Online]. Available: http://enablingthefuture. org/about/. (Accessed: 2018.02.20).
[6] P. Slade, A. Akhtar, M. Nguyen, and T. Bretl, “Tact: Design and performance of an open-source, affordable, myoelectric prosthetic hand”, in Robotics and
Automation (ICRA), 2015 IEEE International Conference on, IEEE, 2015,
pp. 6451–6456.
[7] J. Gibbard. (2013). Dextrus hand, [Online]. Available: http://www.openhandproject. org/dextrus.php. (Accessed: 2018.02.21).
[8] UCFArmory. (2014). Limbitless arm, [Online]. Available: http://enablingthefuture. org/upper-limb-prosthetics/the-limbitless-arm/. (Accessed: 2018.02.21). [9] J. Diamond. (2015). Whippletree in e-nable hand, [Online]. Available: https:
//www.youtube.com/watch?v=dW5B_CeJtd8. (Accessed: 2018.02.21).
[10] Jagwire. (2018). Inner wire guide, [Online]. Available: https : / / jagwire . com/guides/inner-wire. (Accessed: 2018.02.22).
[11] K. R. Mills, “The basics of electromyography”, Journal of Neurology,
Neuro-surgery & Psychiatry, vol. 76, no. suppl 2, pp. ii32–ii35, 2005, issn: 0022-3050.
[12] H. Johansson, P.-E. Lindahl, R. Meyer, M. Grimheden, W. Sandqvist, and M. Paulson, Elektroteknik. Institution for Machine Design, Stockholm: KTH Industrial engineering and Management, 2013.
[13] D. W. Jones. (1995). Control of stepping motors, [Online]. Available: http: / / homepage . divms . uiowa . edu / ~jones / step / index . html. (Accessed: 2018.02.22).
[14] (2011). Flexy hand 2, [Online]. Available: http://enablingthefuture.org/ upper-limb-prosthetics/the-flexy-hand/. (Accessed: 2018.04.01). [15] (2015). V.2 flexy fingers, [Online]. Available: https : / / www . thingiverse .
com/thing:1108085. (Accessed: 2018.04.01).
Appendix A
Arduino Code
// M o t o r i z e d T e n s i o n e r System For P r o s t h e t i c Hands
// A B a c h e l o r t h e s i s i n M e c h a t r o n i c s a t KTH Royal I n s t i t u t e o f T ech no log y // J o n a s Tjomsland & F e l i x H a r d e l l
// May 2018
// I n i t i a l i z i n g v a r i a b l e s : // Hand :
// I n d i c a t e s whether t h e hand i s opened ( 1 ) o r c l o s e d ( 0 ) . i n t h a n d S t a t e ; // Motor : // Standby i s s e t t o p i n 1 3 : i n t STBY = 1 0 ; // Motor i n p u t 1 i s s e t t o p i n 1 2 : i n t m o t o r I n p u t 1 = 9 ; // Motor i n p u t 2 i s s e t t o p i n 1 1 : i n t m o t o r I n p u t 2 = 8 ; // EMG s e n s o r :
// Micro s w i t c h power i s p r o v i d e d from p i n 4 : i n t s w i t c h P o w e r S o u r c e = 4 ;
// Move f u n c t i o n .
// Takes d i r e c t i o n a s i n p u t and r o t a t e s t h e motor . . . // i n t h a t d i r e c t i o n u n t i l t h e s t o p f u n c t i o n i s c a l l e d . v o i d move ( i n t d i r e c t i o n ) { // S e t s s t a n d b y t o HIGH, e n a b l i n g motor r o t a t i o n : d i g i t a l W r i t e (STBY, HIGH ) ; // C l o c k w i s e r o t a t i o n : i f ( d i r e c t i o n == 1 ) { d i g i t a l W r i t e ( motorInput1 , HIGH ) ; d i g i t a l W r i t e ( motorInput2 , LOW) ; } // Counter c l o c k w i s e r o t a t i o n : e l s e { d i g i t a l W r i t e ( motorInput1 , LOW) ; d i g i t a l W r i t e ( motorInput2 , HIGH ) ; } } // Stop f u n c t i o n . // Takes no i n p u t , s t o p s motor r o t a t i o n . v o i d s t o p ( ) { // S e t s s t a n d b y t o LOW, d i s a b l i n g motor r o t a t i o n : d i g i t a l W r i t e (STBY, LOW) ; } // Setup f u n c t i o n . // I n i t i a l i z i n g a l l p i n s and makes s u r e t h a t . . .
// hand i s i n open p o s i t i o n b e f o r e main l o o p s t a r t s . v o i d s e t u p ( ) {
pinMode (STBY, OUTPUT) ;
pinMode ( motorInput1 , OUTPUT) ; pinMode ( motorInput2 , OUTPUT) ; pinMode ( s w i t c h I n p u t , INPUT ) ;
APPENDIX A. ARDUINO CODE // S e t s t h e s w i t c h power s o u r c e ( p i n 4 ) t o HIGH : d i g i t a l W r i t e ( s w i t c h P o w e r S o u r c e , HIGH ) ; // S e t s h a n d s S t a t e t o t h e s w i t c h p o s i t i o n , 1 o r 0 : h a n d S t a t e = d i g i t a l R e a d ( s w i t c h I n p u t ) ; // Open hand i f c l o s e d : i f ( h a n d S t a t e == 0 ) { move ( 1 ) ; // C o n t i n u o u s l y r e a d t h e s w i t c h p o s i t i o n and s t o p . . . // r o t a t i o n when t h e hand i s f u l l y opened :
w h i l e ( 1 ) { h a n d S t a t e = d i g i t a l R e a d ( s w i t c h I n p u t ) ; i f ( h a n d S t a t e == 1 ) { // S t o p s motor r o t a t i o n : s t o p ( ) ; h a n d S t a t e = 1 ; b r e a k ; } d e l a y ( 1 0 0 ) ; } } } // Main l o o p : // S e e s o f t w a r e f l o w c h a r t i n Appendix f o r t h o r o u g h e x p l e n a t i o n o f p r o c e s s . v o i d l o o p ( ) { // Reads t h e EMG s e n s o r v a l u e :
emgValue = analogRead ( analogInputEmg ) ;
// S t o p s motor r o t a t i o n : s t o p ( ) ;
h a n d S t a t e = 0 ; }
// Reads t h e EMG s e n s o r v a l u e :
emgValue = analogRead ( analogInputEmg ) ;
// I f EMG v a l u e i s o v e r t r e s h o l d and hand i s c l o s e d −> open hand : i f ( ( emgValue > t h r e s h o l d V a l u e )&&( h a n d S t a t e == 0 ) )
{
move ( 1 ) ;
// C o n t i n u o u s l y r e a d t h e s w i t c h p o s i t i o n and . . . // s t o p r o t a t i o n when t h e hand i s f u l l y opened :
Appendix B
Flexy Hand 2
BILL OF MATERIALS ITEM NUMBER DESCRIPTION NUMBER OFF 1-1 THUMB PROXIMAL PHALANX 1 1-2 THUMB DISTAL PHALANX 1 2-1 INDEX PROXIMAL PHALANX 1 2-2 INDEX MIDDLE PHALANX 1 2-3 INDEX DISTAL PHALANX 1 3-1 LONG PROXIMAL PHALANX 1 3-2 LONG MIDDLE PHALANX 1 3-3 LONG DISTAL PHALANX 1 4-1 RING PROXIMAL PHALANX 1 4-2 RING MIDDLE PHALANX 1 4-3 RING DISTAL PHALANX 1 5-1 SMALL PROXIMAL PHALANX 1 5-2 SMALL MIDDLE PHALANX 1 5-3 SMALL DISTAL PHALANX 1 6 HAND BODY 1 7 PALMAR DIGITAL 4 8 PROXIMAL AND DISTAL INTERPHALANGEAL 11Redesign of Flexy Hand 2 arm part
Appendix D
Finger configuration of whippletree
Compression spring
1
2
3
Appendix F
Price list of all components
This project was aiming for users in a printing community. Therefore, no 3D-printing materials nor 3D-printers have been taken into consideration when doing this price list. The same goes for soldering, which was also needed.
Price List
Component Model Price
(SEK)
Website Microcontroller Arduino Uno Rev. 3 250 www.kjell.com
Motor DMN29BA-002 250 (1)
Motor driver L298 79 www.electrokit.com
EMG sensor MyoWare Muscle Sensor 332 www.sparkfun.com EMG nodes Muscle Sensor Surface
EMG Electrodes (6-pack)
43 www.sparkfun.com
Micro switch Goobay 10185 19 www.electrokit.com
Electric wires 15 (1)
Bowden cable 150 www.sportson.se
Spring 15 (1)
Fishing line Power Pro 135m (30 kg) 5 www.fiske.se (2)
AA-batteries (LR6) 20-pack 70 www.kjell.com
Battery hold-ers 2x(8x AA med batterikon-takt) 100 www.kjell.com Total 1328
(1) Was provided by the Department of Machine Design at KTH Royal Institute of Technology. Prices have been estimates according to market value as of May 20 2018.
DMN29
Series
■Specification ■Outline DMN29 DMN29BA 3.0 12 7.8 1.11 0.42 3700 0.07 5000 30 4.17 90 0.20 DMN29BB 3.0 24 7.8 1.11 0.21 3700 0.05 5000 30 4.17 90 0.20 TYPERATED NO LOAD STALL
WEIGHT
g lb
TORQUE CURRENT SPEED
VOLTAGE OUT PUT mN・m V W oz・in A CURRENT A SPEED
r/min r/min mN・m oz・in
TORQUE TORQUE 0 0 10 20 30 40 0 1000 2000 3000 4000 5000 6000 7000 5 10 15 20 25 30 35mN・m SPEED CURRENT CURREN T SP EED RED HOLDER CW （＋） （−） BLACK HOLDER oz・in 100 200 300 gf・cm 0 0.8 2.4 2.0 SPEED （r/min） CURRENT(A) : 24V 0 0.4 1.2 1.0 2.8 1.4 CURRENT(A) : 12V 1.6 0.8 1.2 0.6 0.4 0.2
■CURRENT, SPEED-TORQUE CURVE ■CONNECTION
24.6 (0.969) (RED) (+)TERMINAL (BLACK) (-)TERMINAL 2-M2.6DEPTH 3MAX (0.118 MAX) HOLE φ (0.098dia.) 2.5 10 (0.394) NAME PLATE P.C.D=φ16 (P.C.D=0.63dia. ) ±0.2 ±0.008 0.8 2-φ (2-0.047dia. ) ±0.2 ±0.008 1.2 ２ − 2.8 × 0.5 t 6.2 1.5
(+)(-) TERMINAL DETAILED DRAWING
■DIMENSIONS Unit mm(inch)
φ -0.01 0 2.5 12 2.7 38.8 (1.528) 3.2 φ 10 φ -0.1 0 10 φ27.8 (1.094dia.) φ29 (1.142dia.) (0.098dia. ) (0.394dia.) (2-0.110 × 0.02 t ) 0 -0.0004 (0.394dia. ) 0 -0.004 (0.126) (0.106) (0.032) (0.244) (0.059) (0.472)
DC Brush Motors
DMN29 Motor
※ SPEED CURRENT ■Outline ■Outline DMN29BL□◇
A
Intermittent Operation 21.5 (0.847) 5 (0.197) 15.5 (0.61) 10.5 (0.413) ±0 .1 5 φ -0.02 0 6 φ 10 4-0.5 (4-0.02) 17.9 (0.705) (RED) (+)TERMINAL (BLACK) (-)TERMINAL NAME PLATE DMN29BA-002, 003 φ1.2 HOLE φ3+0.1 0 ± 0.5 2-2.8 (0.3594dia.) (2-0.11 ) (1.142dia.) (3.937) (0.047dia.) (0.217) (0.736) (0.638) (0.236) (0.276) ± 0.02 (0.197 ± 0.004 ) (0.315 ) 0 -0.0008 7 3.2 φ 29 φ 10 56.8 100 5.5 18.7 6 16.2 φ -0.02 0 8 ■Specification GEAR RATIO※Rotation of gearbox shaft is in reverse of rotation of motor. 78.9 RATED TORQUE 0.190 N・m 27.8 oz・in r/min SPEED 56 DMN29BA-002 DMN29BA-003
L
Intermittent Operation ■Specification※Enter the required reduction ratio in the □. ※Enter the required voltage A or B in the ◇.
WEIGHT：140g 0.31 lb WEIGHT：250g 0.55 lb GEAR RATIO 30 50 120 150 200 255 RATED TORQUE 0.14 0.23 0.56 0.69 0.92 0.98 N・m 19.5 32.0 77.9 90.8 131 139 oz・in r/min 123 74.0 30.8 24.7 18.5 15.3 DMN29BL□◇
■DIMENSIONS Unit mm(inch)
■DIMENSIONS Unit mm(inch)
Appendix H
Appendix I
Measuring muscle activation via electric potential, referred to as electromyography (EMG), has
traditionally been used for medical research and diagnosis of neuromuscular disorders. However,
with the advent of ever shrinking yet more powerful microcontrollers and integrated circuits, EMG
circuits and sensors have found their way into prosthetics, robotics and other control systems.
3-lead Muscle / Electromyography
Sensor for Microcontroller Applications
FEATURES
NEW - Wearable Design
NEW - Single Supply
+3.1V to +5.9V
Polarity reversal protection
NEW - Two Output Modes
EMG Envelope
Raw EMG
NEW - Expandable via Shields
NEW - LED Indicators
Specially Designed For Microcontrollers
Adjustable Gain
1 - Power Supply, +Vs
2 - Power Supply, GND
3 - Output Signal, SIG
Sensor Layout
What is electromyography?
Raw EMG Signal - 7
Shield Power (output) - 8
Shield GND- 9
4 - Mid Muscle Electrode Pin
5 - End Muscle Electrode Pin
6 - Reference Electrode Pin
Reference Electrode Cable
Adjustable Gain
(SIG Output Only)
Mid Muscle Electrode Snap
End Muscle Electrode Snap
MyoWare™ Muscle Sensor (AT-04-001)
DATASHEET
Note: Isolator model is only
a suggestion.
Setup Configurations
(Arduino is shown but MyoWare is compatible with most development boards)a) Battery powered with isolation via no direct external connections
b) Grid powered with USB isolation
Note: Since no component is
connected to electrical grid,
further isolation is not
required. It is also
acceptable to power the
MCU with a battery via the
USB or barrel ports.
c) Battery powered sensor, Grid powered MCU with USB isolation
Setup Configurations (cont’d)
d) Grid powered. Warning: No isolation.
Note: This configuration has no
isolation. Usually safe but rare
situations could create a
current loop to the electrical
grid.
Note: Isolator model is only
Setup Instructions
1)
Thoroughly clean the intended area with soap to remove dirt and oil
2)
Snap electrodes to the sensor’s snap connectors
(Note: While you can snap the sensor to the electrodes after they’ve been placed on the muscle, we do not
recommend doing so due to the possibility of excessive force being applied and bruising the skin.)
3)
Place the sensor on the desired muscle
a.
After determining which muscle group you want to target (e.g. bicep, forearm,
calf), clean the skin thoroughly
b.
Place the sensor so one of the connected electrodes is in the middle of the
muscle body. The other electrode should line up in the direction of the muscle
length
c.
Peel off the backs of the electrodes to expose the adhesive and apply them to
the skin
d.
Place the reference electrode on a bony or nonadjacent muscular part of your
body near the targeted muscle
4)
Connect to a development board (e.g. Arduino, RaspberryPi), microcontroller, or ADC
a.
See configurations previously shown
Example Sensor Location for Bicep
© 2015-2016
Why is electrode placement important?
Raw EMG output
Innervation Zone
Correct Placement
Midline of the muscle belly
between an innervation zone
and a myotendon junction
Midline Offset
Myotendon Junction
RAW EMG vs EMG Envelope
Our Muscle Sensors are designed to be used directly with a microcontroller. Therefore, our
sensors primary output is not a RAW EMG signal but rather an amplified, rectified, and
integrated signal (AKA the EMG’s envelope) that will work well with a microcontroller’s
analog-to-digital converter (ADC). This difference is illustrated below using a
representative EMG signal.
Note: Actual sensor output not shown.
RAW EMG Signal
Rectified EMG Signal
Rectified & Integrated
EMG Signal
Reconfigure for Raw EMG Output
This new version has the ability to output an amplified raw EMG signal.
To output the raw EMG signal, simply connect the raw EMG signal pin to your measuring
device instead of the SIG pin.
Connect
© 2015-2016
Note: The RAW output is centered about an
offset voltage of +Vs/2, see above. It is
important to ensure +Vs is the max voltage
of the MCU’s analog to digital converter. This
will assure that you completely see both
positive and negative portions of the
waveform.
Connecting external electrode cables
Re f En d M id d leThis new version has embedded electrode
snaps right on the sensor board itself,
replacing the need for a cable. However, if
the on board snaps do not fit a user’s
specific application, an external cable can
be connected to the board through three
through hole pads shown above.
Middle
Connect this pad to the cable leading to an
electrode placed in the middle of the muscle body.
End
Connect this to the cable leading to an electrode
placed adjacent to the middle electrode towards
the end of the muscle body.
Ref
Connect this to the reference electrode. The
reference electrode should be placed on an
separate section of the body, such as the bony
portion of the elbow or a nonadjacent muscle
Adjusting the gain
We recommend for users to get their sensor setup working reliably prior to adjusting the
gain. The default gain setting should be appropriate for most applications.
To adjust the gain, locate the gain potentiometer in the lower left corner of the sensor
(marked as “GAIN”). Using a Phillips screwdriver, turn the potentiometer clockwise to
increase the output gain; turn the potentiometer counterclockwise to reduce the gain.
Electrical Specifications
Parameter
Min
TYP
Max
Supply Voltage
+3.1V
+3.3V or +5V
+6.3V
Adjustable Gain Potentiometer, R
gain(G = 201 * R
gain/ 1 kΩ)
0.01 Ω
50 kΩ
100 kΩ
Output Signal Voltage
EMG Envelope
Raw EMG (centered about +Vs/2)
0V
0V
--+Vs
+Vs
Input Impedance
--
110 GΩ
--Supply Current
--
9 mA
14 mA
Common Mode Rejection Ratio (CMRR)
--
110
--Input Bias
--
1 pA
--Dimensions
© 2015-2016
0.82 (20.7) 2.06 (52.3)L298
DUAL FULL-BRIDGE DRIVER
Multiwatt15
ORDERING NUMBERS : L298N (Multiwatt Vert.)
L298HN (Multiwatt Horiz.) L298P (PowerSO20)
BLOCK DIAGRAM
.
OPERATING SUPPLY VOLTAGE UP TO 46 V.
TOTAL DC CURRENT UP TO 4 A.
LOW SATURATION VOLTAGE.
OVERTEMPERATURE PROTECTION.
LOGICAL "0" INPUT VOLTAGE UP TO 1.5 V(HIGH NOISE IMMUNITY)
DESCRIPTION
The L298 is an integrated monolithic circuit in a 15-lead Multiwatt and PowerSO20 packages. It is a high voltage, high current dual full-bridge driver de-signed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors. Two enable inputs are provided to enable or disable the device independently of the in-put signals. The emitters of the lower transistors of each bridge are connected together and the corre-sponding external terminal can be used for the
con-nection of an external sensing resistor. An additional supply input is provided so that the logic works at a lower voltage.
PowerSO20
PIN CONNECTIONS (top view) GND Input 2 VSS N.C. Out 1 VS Out 2 Input 1 Enable A Sense A GND 10 8 9 7 6 5 4 3 2 13 14 15 16 17 19 18 20 12 1 11 GND D95IN239 Input 3 Enable B Out 3 Input 4 Out 4 N.C. Sense B GND
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VS Power Supply 50 V
VSS Logic Supply Voltage 7 V
VI,Ven Input and Enable Voltage –0.3 to 7 V
IO Peak Output Current (each Channel)
– Non Repetitive (t = 100µs) –Repetitive (80% on –20% off; ton = 10ms) –DC Operation 3 2.5 2 A A A
Vsens Sensing Voltage –1 to 2.3 V
Ptot Total Power Dissipation (Tcase = 75°C) 25 W
Top Junction Operating Temperature –25 to 130 °C
Tstg, Tj Storage and Junction Temperature –40 to 150 °C
THERMAL DATA
Symbol Parameter PowerSO20 Multiwatt15 Unit
Rth j-case Thermal Resistance Junction-case Max. – 3 °C/W
Rth j-amb Thermal Resistance Junction-ambient Max. 13 (*) 35 °C/W 1 2 3 4 5 6 7 9 10 11 8 ENABLE B INPUT 3
LOGIC SUPPLY VOLTAGE VSS
GND INPUT 2 ENABLE A INPUT 1 SUPPLY VOLTAGE VS OUTPUT 2 OUTPUT 1 CURRENT SENSING A
TAB CONNECTED TO PIN 8
PIN FUNCTIONS (refer to the block diagram)
MW.15 PowerSO Name Function
1;15 2;19 Sense A; Sense B Between this pin and ground is connected the sense resistor to
control the current of the load.
2;3 4;5 Out 1; Out 2 Outputs of the Bridge A; the current that flows through the load
connected between these two pins is monitored at pin 1.
4 6 VS Supply Voltage for the Power Output Stages.
A non-inductive 100nF capacitor must be connected between this pin and ground.
5;7 7;9 Input 1; Input 2 TTL Compatible Inputs of the Bridge A.
6;11 8;14 Enable A; Enable B TTL Compatible Enable Input: the L state disables the bridge A
(enable A) and/or the bridge B (enable B).
8 1,10,11,20 GND Ground.
9 12 VSS Supply Voltage for the Logic Blocks. A100nF capacitor must be
connected between this pin and ground.
10; 12 13;15 Input 3; Input 4 TTL Compatible Inputs of the Bridge B.
13; 14 16;17 Out 3; Out 4 Outputs of the Bridge B. The current that flows through the load
connected between these two pins is monitored at pin 15.
– 3;18 N.C. Not Connected
ELECTRICAL CHARACTERISTICS (VS = 42V; VSS = 5V, Tj = 25°C; unless otherwise specified)
Symbol Parameter Test Conditions Min. Typ. Max. Unit
VS Supply Voltage (pin 4) Operative Condition VIH +2.5 46 V
VSS Logic Supply Voltage (pin 9) 4.5 5 7 V
IS Quiescent Supply Current (pin 4) Ven = H; IL = 0 Vi = L
Vi = H 13 50 22 70 mA mA Ven = L Vi = X 4 mA
ISS Quiescent Current from VSS (pin 9) Ven = H; IL = 0 Vi = L
Vi = H 24 7 36 12 mA mA Ven = L Vi = X 6 mA
ViL Input Low Voltage
(pins 5, 7, 10, 12)
–0.3 1.5 V
ViH Input High Voltage
(pins 5, 7, 10, 12)
2.3 VSS V
IiL Low Voltage Input Current
(pins 5, 7, 10, 12)
Vi = L –10 µA
IiH High Voltage Input Current
(pins 5, 7, 10, 12)
Vi = H ≤ VSS –0.6V 30 100 µA
Ven = L Enable Low Voltage (pins 6, 11) –0.3 1.5 V
Ven = H Enable High Voltage (pins 6, 11) 2.3 VSS V
Ien = L Low Voltage Enable Current
(pins 6, 11)
Ven = L –10 µA
Ien = H High Voltage Enable Current
(pins 6, 11)
Ven = H ≤ VSS –0.6V 30 100 µA
VCEsat (H) Source Saturation Voltage IL = 1A
IL = 2A 0.95 1.35 2 1.7 2.7 V V VCEsat (L) Sink Saturation Voltage IL = 1A (5)
IL = 2A (5) 0.85 1.2 1.7 1.6 2.3 V V VCEsat Total Drop IL = 1A (5)
IL = 2A (5)
1.80 3.2
4.9 V V
Vsens Sensing Voltage (pins 1, 15) –1 (1) 2 V
Figure 1 : Typical Saturation Voltage vs. Output
Current.
Figure 2 : Switching Times Test Circuits.
Note : For INPUT Switching, set EN = H
For ENABLE Switching, set IN = H 1) 1)Sensing voltage can be –1 V for t ≤ 50 µsec; in steady state Vsens min ≥ – 0.5 V.
2) See fig. 2. 3) See fig. 4.
4) The load must be a pure resistor.
ELECTRICAL CHARACTERISTICS (continued)
Symbol Parameter Test Conditions Min. Typ. Max. Unit
T1 (Vi) Source Current Turn-off Delay 0.5 Vi to 0.9 IL (2); (4) 1.5 µs
T2 (Vi) Source Current Fall Time 0.9 IL to 0.1 IL (2); (4) 0.2 µs
T3 (Vi) Source Current Turn-on Delay 0.5 Vi to 0.1 IL (2); (4) 2 µs
T4 (Vi) Source Current Rise Time 0.1 IL to 0.9 IL (2); (4) 0.7 µs
T5 (Vi) Sink Current Turn-off Delay 0.5 Vi to 0.9 IL (3); (4) 0.7 µs
T6 (Vi) Sink Current Fall Time 0.9 IL to 0.1 IL (3); (4) 0.25 µs
T7 (Vi) Sink Current Turn-on Delay 0.5 Vi to 0.9 IL (3); (4) 1.6 µs
T8 (Vi) Sink Current Rise Time 0.1 IL to 0.9 IL (3); (4) 0.2 µs
fc (Vi) Commutation Frequency IL = 2A 25 40 KHz
T1 (Ven) Source Current Turn-off Delay 0.5 Ven to 0.9 IL (2); (4) 3 µs
T2 (Ven) Source Current Fall Time 0.9 IL to 0.1 IL (2); (4) 1 µs
T3 (Ven) Source Current Turn-on Delay 0.5 Ven to 0.1 IL (2); (4) 0.3 µs
T4 (Ven) Source Current Rise Time 0.1 IL to 0.9 IL (2); (4) 0.4 µs
T5 (Ven) Sink Current Turn-off Delay 0.5 Ven to 0.9 IL (3); (4) 2.2 µs
T6 (Ven) Sink Current Fall Time 0.9 IL to 0.1 IL (3); (4) 0.35 µs
T7 (Ven) Sink Current Turn-on Delay 0.5 Ven to 0.9 IL (3); (4) 0.25 µs
Figure 3 : Source Current Delay Times vs. Input or Enable Switching.
Figure 4 : Switching Times Test Circuits.
Note : For INPUT Switching, set EN = H
For ENABLE Switching, set IN = L
Figure 5 : Sink Current Delay Times vs. Input 0 V Enable Switching.
Figure 6 : Bidirectional DC Motor Control.
L = Low H = High X = Don’t care
Inputs Function
Ven = H C = H ; D = L Forward
C = L ; D = H Reverse
C = D Fast Motor Stop
Ven = L C = X ; D = X Free Running
Figure 7 : For higher currents, outputs can be paralleled. Take care to parallel channel 1 with channel 4
and channel 2 with channel 3.
APPLICATION INFORMATION (Refer to the block diagram)
1.1. POWER OUTPUT STAGE
The L298 integrates two power output stages (A ; B). The power output stage is a bridge configuration and its outputs can drive an inductive load in com-mon or differenzial mode, depending on the state of the inputs. The current that flows through the load comes out from the bridge at the sense output : an external resistor (RSA ; RSB.) allows to detect the
in-tensity of this current. 1.2. INPUT STAGE
Each bridge is driven by means of four gates the in-put of which are In1 ; In2 ; EnA and In3 ; In4 ; EnB. The In inputs set the bridge state when The En input is high ; a low state of the En input inhibits the bridge. All the inputs are TTL compatible.
2. SUGGESTIONS
A non inductive capacitor, usually of 100 nF, must be foreseen between both Vs and Vss, to ground, as near as possible to GND pin. When the large ca-pacitor of the power supply is too far from the IC, a second smaller one must be foreseen near the L298.
The sense resistor, not of a wire wound type, must be grounded near the negative pole of Vs that must be near the GND pin of the I.C.
Each input must be connected to the source of the driving signals by means of a very short path. Turn-On and Turn-Off : Before to Turn-ON the Sup-ply Voltage and before to Turn it OFF, the Enable in-put must be driven to the Low state.
3. APPLICATIONS
Fig 6 shows a bidirectional DC motor control Sche-matic Diagram for which only one bridge is needed. The external bridge of diodes D1 to D4 is made by four fast recovery elements (trr ≤ 200 nsec) that must be chosen of a VF as low as possible at the worst case of the load current.
The sense output voltage can be used to control the current amplitude by chopping the inputs, or to pro-vide overcurrent protection by switching low the en-able input.
The brake function (Fast motor stop) requires that the Absolute Maximum Rating of 2 Amps must never be overcome.
When the repetitive peak current needed from the load is higher than 2 Amps, a paralleled configura-tion can be chosen (See Fig.7).
An external bridge of diodes are required when in-ductive loads are driven and when the inputs of the IC are chopped ; Shottky diodes would be preferred.
This solution can drive until 3 Amps In DC operation and until 3.5 Amps of a repetitive peak current. On Fig 8 it is shown the driving of a two phase bipolar stepper motor ; the needed signals to drive the in-puts of the L298 are generated, in this example, from the IC L297.
Fig 9 shows an example of P.C.B. designed for the application of Fig 8.
Fig 10 shows a second two phase bipolar stepper motor control circuit where the current is controlled by the I.C. L6506.
Figure 8 : Two Phase Bipolar Stepper Motor Circuit.
This circuit drives bipolar stepper motors with winding currents up to 2 A. The diodes are fast 2 A types.
RS1 = RS2 = 0.5 Ω
Figure 9 : Suggested Printed Circuit Board Layout for the Circuit of fig. 8 (1:1 scale).
Figure 10 : Two Phase Bipolar Stepper Motor Control Circuit by Using the Current Controller L6506.
RR and Rsense depend from the load current
Multiwatt15 V
DIM. mm inch
MIN. TYP. MAX. MIN. TYP. MAX.
DIM. mm inch
MIN. TYP. MAX. MIN. TYP. MAX.
JEDEC MO-166
PowerSO20
e a2 A E a1 PSO20MEC DETAIL A T D 1 11 20 E1 E2 h x 45 DETAIL A lead slug a3 S Gage Plane 0.35 L DETAIL B R DETAIL B (COPLANARITY) G C C -SEATING PLANE e3 b c N N H BOTTOM VIEW E3 D1 DIM. mm inchMIN. TYP. MAX. MIN. TYP. MAX.
A 3.6 0.142 a1 0.1 0.3 0.004 0.012 a2 3.3 0.130 a3 0 0.1 0.000 0.004 b 0.4 0.53 0.016 0.021 c 0.23 0.32 0.009 0.013 D (1) 15.8 16 0.622 0.630 D1 9.4 9.8 0.370 0.386 E 13.9 14.5 0.547 0.570 e 1.27 0.050 e3 11.43 0.450 E1 (1) 10.9 11.1 0.429 0.437 E2 2.9 0.114 E3 5.8 6.2 0.228 0.244 G 0 0.1 0.000 0.004 H 15.5 15.9 0.610 0.626 h 1.1 0.043 L 0.8 1.1 0.031 0.043 N 10˚ (max.) S T 10 0.394
(1) "D and F" do not include mold flash or protrusions. - Mold flash or protrusions shall not exceed 0.15 mm (0.006"). - Critical dimensions: "E", "G" and "a3"
OUTLINE AND MECHANICAL DATA
8˚ (max.)
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the conse-quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi-croelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
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