How to Test the Performance of an Exoskeleton

Table of Links

Abstract and 1 Introduction

2 Results

2.1 Initial Processed Data for a Representative Participant

2.2 Overall Performance Analysis

2.3 Interaction Portrait Analysis

2.4 Individual Adaptation Strategy

3 Discussion

3.1 Human Adaptation

3.2 Importance of IP Analysis

4 Conclusion

5 Methods

5.1 Feedforward Control Strategies

5.2 Experimental Setup

5.3 Experimental Protocol

5.4 Data Analysis

Declarations

Appendix A Complementary Example Data

Appendix B Comparison with Natural Walking

References

5.2 Experimental Setup

The experimental setup comprised a split-belt instrumented treadmill (Bertec, US), with force plates under each belt, providing ground reaction forces (GRF) under each belt, a lower limb exoskeleton (Indego, Parker Hannifin, US) with actuated hip and knee joints, fourteen wireless EMG sensors (Trigno, Delsys, USA), and a COSMED K5 wearable metabolic system (Albano Laziale, Roma, Italy) to measure oxygen uptake (VO2). Additionally, four Physilog IMUs (Physilog 6s, Gait Up SA, CH) and a COSMED K5 wearable metabolic system (Albano Laziale, Roma, Italy) are employed to measure gait spatiotemporal parameters and oxygen uptake (VO2), respectively. The exoskeleton, IMUs, load cells, and EMG sensors have sampling rates of 200 Hz, 128 Hz, 1000 Hz, and 2000 Hz, respectively. Following appropriate skin treatment, EMG sensors were placed on Gluteus Maximus, Biceps Femoris, Rectus Femoris, Vastus Medialis, Gastrocnemius Medialis, Soleus, and Tibialis Anterior muscles of each leg. Spatiotemporal gait parameters such as Minimum Toe Clearance (minTC), Maximum Heel Clearance (maxHC), Stance Time Percentage, and Stride Length are computed

Fig. 9 Dorsal, lateral, and frontal view of a participant with the Indego exoskeleton with active hip and knee joints. The participant is standing on the Bertec treadmill with two speed-controlled belts equipped with individual loadcells underneath each of them for GRF monitoring. Muscle activation is measured from both right and left leg muscles using EMG sensors. Gait up IMUs are clipped to the outer side of the shoes right bellow ankle joints to measure the spatiotemporal parameters of gait. Oxygen uptake of the participant is measured and recorder at each breath through a mask connected to the gas analyzer device carried at the back of the participant.

using the Physilog sensors, as validated in previous studies [30, 31]. Before recording data for each subject, the COSMED K5 underwent a calibration process following a standardized procedure. Fig. 9 illustrates the exoskeleton and the placement of the sensors within the experimental setup.

5.3 Experimental Protocol

The experiment consisted of three blocks, each involving participants walking on the treadmill with the exoskeleton controlled by one of three different controllers: TBC, HTC, or AMTC. The order of the blocks was varied among participants to mitigate any potential order effects. Within each block, participants walked at three distinct speeds: ultra-slow (0.4 m/s), slow (0.6 m/s), and moderate (0.8 m/s). Each speed lasted for a duration of 100 seconds. For an illustration of the treadmill speed and the order of the controllers applied to the exoskeleton for participant #1, refer to Fig. 10.

A total of nine able-bodied participants (5 males and 4 females, age: 23.4±4.2 years, mass: 73.6±20.2 kg, height: 176.7±9.6 cm) participated in the study. All participants provided informed written consent prior to the experiments. The study protocol and procedures received ethical approval from the University of Waterloo Clinical Research Ethics Committee (ORE#41794). The study adhered to the principles outlined in the Declaration of Helsinki.

Fig. 10 Treadmill speed changes while experimenting with the HTC, AMTC, and the TBC controller. The order of the controllers was specific to participant #1 and varied for other participants. Participants walked with each controller for 300 seconds divided by three 100-second walking periods during each the treadmill speed was set to ultra-slow (0.4 m/s), slow (0.6 m/s), and moderate (0.8 m/s) speeds.