Daniel Eriksson
Örebro University, School of Science and Technology Fakultetsgatan 1
SE-701 82 Örebro Sweden
Tel:
Email: daniel.eriksson@oru.se Supervisor: Christer Korin
Tactile sensing of carton quality
1. Introduction
A minimum requirement for any package is that it should be able to withstand the forces that it will be subjected to when manipulated by consumers. The package should not break, and the contents should stay safe inside the package when it is lifted, opened, or manipulated in any other way. These requirements on strength and stiffness constitute a form of objective requirements. Objective in the sense that they can be deduced from a mechanical analysis of the use case.
Understanding the objective requirements is necessary, but no sufficient, for designing a package for manual handling. There are also subjective requirements on packaging. Even if a package is not damaged, consumers may still reject it based on the sensation of touching it.
Löfgren proposed the concepts of the “first and second moments of truth” for understanding the different roles of packaging [1]. The first moment of truth is when the buying decision happens at the point of retail. The second moment of truth is when the product is used by the consumer. The concepts of first and second moments of truth are useful for tactile aspects of packaging since they label the two points at which consumers interact with the package.
Being in the right position and having an attention-grabbing visual appearance is crucial if a product should even be considered for purchase. However, once the consumer has made her decision, she reaches out to touch the package. As her fingers wrap around the package, the expectations she has built up based on the appearance of the package are put to the test. If the package looks luxurious, but is flimsy to touch, will she not reevaluate her judgement of the product? Likewise, when a product is used, the consumer will inevitably interact with its packaging using her hands.
The relative importance of touch for product judgement and buying decisions varies between commodities. For some product, e.g. textiles, it is essential; for others it is merely an extra dimension. This extra dimension can nevertheless add value to the offering. The same water may taste better when served in a glass rather than when served a plastic cup [2] or it may taste better when served in a firm cup than when served in a flimsy cup [3]. Food may be perceived as more crunchy when its package is given a rougher surface [4].
The aim of this project is to devise a systematic approach to dealing issues related to manual handling of board packages, both in an objective and in a subjective sense.
2. Materials and Methods
For testing the objective requirements on package strength, a rigid spherical indenter is used. The indenter pushes against the package at a constant displacement rate while the force is measured. This results in a distinct damage pattern that is similar to what has been observed on packages damaged by manual handling.
For testing subjective requirements, this method is lacking because it gives only information on the total displacement. The sense of touch is really two senses, proprioception, the sensation of movement of limbs, and tactition, the sensation of skin deformations [5]. It has been shown that humans judge compliance based on a combination of proprioceptive and tactile cues [6].
A biomimetic tactile sensor (BioTac, Syntouch LLC) is used for these tests, see Figure 1. This sensor is capable of registering a variety of signals [7]. While this sensor has not been used on carton board packages before, it has been successfully used to classify objects and to characterize surfaces [7–10].
3. Results
By studying packages damaged by manual handling, a typical pattern of damage to carton board packages has been identified. It has been possible to replicate this pattern in the lab using a tensile testing machine and rigid spherical indenters. The maximum load that the package could sustain showed little sensitivity to the radius of the indenter within the size range that we have tested, while the stiffness was largely dependent on to which degree the stiff transverse panels were loaded. In an experiment using a tactile sensor, a total of twelve packages of three geometries and eight materials were tested. The BioTac sensor was used to compress the package close to the crease. The force and the sensor data were logged during the trials. A snapshot of the sensor data from each trial at a given reference force of 8 N was used to train a nearest neighbour classifier. The performance of the classifier was 85 % when evaluated using 5-fold cross-validation despite deliberate variation in the experimental setup.
4. References
[1] M. Löfgren, “Winning at the first and second moments of truth: an exploratory study,” Managing Service Quality, vol. 15, no. 1, pp. 102–115, 2005.
[2] Y. Tu, Z. Yang, and C. Ma, “Touching tastes: The haptic perception transfer of liquid food packaging materials,” Food Quality and Preference, vol. 39, pp. 124–130, 2015.
[3] A. Krishna and M. Morrin, “Does touch affect taste? The perceptual transfer of product container haptic cues,” Journal of Consumer Research, vol. 34, no. 4, pp. 807–818, 2008.
[4] B. Piqueras-Fiszman and C. Spence, “The influence of the feel of product packaging on the perception of the oral-somatosensory texture of food,” Food Quality and Preference, vol. 26, no. 1, pp. 67–73, 2012.
[5] S. J. Lederman and R. L. Klatzky, “Haptic perception: a tutorial,” Attention, Perception & Psychophysics, vol. 71, pp. 1439–1459, 2009.
[6] W. M. Bergmann Tiest and A. Kappers, “Cues for haptic perception of compliance,” IEEE Transactions on Haptics, vol. 2, pp. 189–199, 2009. [7] J. A. Fishel and G. E. Loeb, “Bayesian exploration for intelligent identification
Figure 1. BioTac sensor.
[8] Z. Su, J. A. Fishel, T. Yamamoto, and G. E. Loeb, “Use of tactile feedback to control exploratory movements to characterize object compliance,” Frontiers in Neurorobotics, vol. 6, pp. 1–9, 2012.
[9] D. Xu, G. E. Loeb, and J. A. Fishel, “Tactile identification of objects using Bayesian exploration,” in IEEE International Conference on Robotics and Automation (ICRA), pp. 3056–3061, 2013.
[10] V. Chu, I. McMahon, L. Riano, C. G. McDonald, Q. He, J. Martinez Perez-Tejada, M. Arrigo, T. Darrell, and K. J. Kuchenbecker, “Robotic learning of haptic adjectives through physical interaction,” Robotics and Autonomous Systems, vol. 63, Part 3, pp. 279–292, 2015.
5. Publications
D. Eriksson and C. Korin, “How small is a point load? – Deformation and failure of carton board packages subjected to non-uniform loads”, Submitted manuscript, 2015.
D. Eriksson, C. Korin, and F. Thuvander, “Damage to Carton Board Packages Subjected to Concentrated Loads”. In Responsible Packaging for a Global Market: Proceedings of the 19th IAPRI World Conference on Packaging, pp. 172–182, 2014.
6. Acknowledgements
This work was supported in part by The Knowledge Foundation (KK-stiftelsen) and Stiftelsen Gunnar Sundblads Forskningsfond. Industrial partners are BillerudKorsnäs and Tetra Pak.
