Integration of Inertial Sensors in a Lower Limb Robotic Exoskeleton

Abstract

Motion assistance exoskeletons are designed to support the joint movement of people who perform repetitive tasks that cause damage to their health. To guarantee motion accompaniment, the integration between sensors and actuators should ensure a near-zero delay between the signal acquisition and the actuator response. This study presents the integration of a platform based on Imocap-GIS inertial sensors, with a motion assistance exoskeleton that generates joint movement by means of Maxon motors and Harmonic drive reducers, where a near zero-lag is required for the gait accompaniment to be correct. The Imocap-GIS sensors acquire positional data from the user's lower limbs and send the information through the UDP protocol to the CompactRio system, which constitutes a high-performance controller. These data are processed by the card and subsequently a control signal is sent to the motors that move the exoskeleton joints. Simulations of the proposed controller performance were conducted. The experimental results show that the motion accompaniment exhibits a delay of between 20 and 30 ms, and consequently, it may be stated that the integration between the exoskeleton and the sensors achieves a high efficiency. In this work, the integration between inertial sensors and an exoskeleton prototype has been proposed, where it is evident that the integration met the initial objective. In addition, the integration between the exoskeleton and IMOCAP is among the highest efficiency ranges of similar systems that are currently being developed, and the response lag that was obtained could be improved by means of the incorporation of complementary systems.

Keywords: Imocap-GIS; UDP protocol; actuators; exoskeleton; inertial sensors; lower limb; motion cycle.

Figure 1

Exoskeleton developed by the GIIB.

Figure 2

Imocap-GIS system.

Figure 3

Connection diagram of the Imocap-GIS system.

Figure 4

(a) Placement of the Imocap-GIS system for collecting information, (b) Flowchart of the experimental procedure.

Figure 5

Control diagram of the Exoskeleton.

Figure 6

Block diagram of the integration.

Figure 7

Exoskeleton Links.

Figure 8

Diagram. (a) Hip Link Diagram (b) Knee Link Diagram.

Figure 9

System Identification.

Figure 10

Controller of the Hip and Knee.

Figure 11

Control Conditions Obtained.

Figure 12

Reference curves vs. output during slow hip motion.

Figure 13

Reference curves vs. output during normal hip motion.

Figure 14

Reference curves vs. output during slow knee motion.

Figure 15

Reference curves vs. output during normal knee motion.