The effect of simulated circumferential soft exoskeleton compression at the knee on discomfort and pain

Abstract

There is a lack of data and guidance on soft exoskeleton pressure contact with the body. The purpose of this research was to study the relationship between circumferential loading at the knee and discomfort/pain, to inform the design of soft exoskeletons/exosuits. The development of discomfort and pain was studied during standing and walking with circumferential compression using a pneumatic cuff.Our results show higher tolerance for intermittent than continuous compression during standing. Discomfort was triggered at pressures ranging from 13.7 kPa (continuous compression) to 30.4 kPa (intermittent compression), and pain at 52.9 kPa (continuous compression) to 60.6 kPa (intermittent compression).During walking, cyclic compression caused an increase in discomfort with time. Higher cuff inflation pressures caused an earlier onset and higher end intensities of discomfort than lower pressures. Cyclic cuff inflation of 10 kPa and 20 kPa was reasonably well tolerated.Practitioner summary: Soft exoskeleton compression of the knee was simulated during static and dynamic compression cycles. The results can be used to understand how users tolerate pressure at the knee, and also to understand the levels at which discomfort and pain are experienced.

Relationship Between Interface Pressures and Pneumatic Cuff Inflation Pressure at Different Assessment Sites of the Lower Limb to Aid Soft Exoskeleton Design

“…The regression equations reported here can be used to predict interface pressures at the typical sites of human-soft exoskeleton contact during circumferential compression. In combination with the data on discomfort and pain reported in our previous studies (Kermavnar, 2019;Kermavnar et al, 2019), we can conclude the following: (1) interface pressures that are likely to cause discomfort are 16.8-37.5 kPa at the thigh, 21.4-90.3 kPa at the calf, and 15.2-37.2 kPa at the knee; and (2) interface pressures that are likely to cause pain are 49.6-75.9 kPa at the thigh, 78.8-90.3 kPa at the calf, and 66.9-77.1 kPa at the knee. The lower limits apply to continuous compression and the higher to intermittent compression.…”

“…Due to their design and function, soft exoskeletons are more likely to exert circumferential compression than point pressure on the body. The findings of this study and our previous studies on discomfort (Kermavnar, 2019;Kermavnar et al, 2019) show that pressures applied to the limbs differ from the pressures transmitted and thus experienced (i.e., interface pressures), depending on the compressed tissue characteristics and the equipment used. The pressures experienced by the wearer determine whether they will perceive discomfort and whether the loading could cause injury to the tissues.…”

“…In a previous study, we addressed the influence of circumferential compression at the thigh, calf, and knee on discomfort and pain in the context of soft exoskeleton design (Kermavnar et al, 2019;Kermavnar, 2019). The discomfort and pain detection thresholds were reported in terms of pneumatic cuff inflation pressures.…”

Soft Wearable Robots: Development Status and Technical Challenges

“…Efforts should be made to guarantee comfort while wearing [ 114 ]. Excessive normal pressure and shear force between the wearer and suit usually make people feel uncomfortable.…”