Evaluation of the Capabilities of a Hybrid Driven Exoskeleton in Passive Mode of Interaction Dimitar Chakarov a , Ivanka Veneva b , Pavel Venev c and Mihail Tsveov d Institute of Mechanics, Bulgarian Academy of Sciences, “Acad. G. Bonchev” str., Block 4, Sofia 1113, Bulgaria Keywords: Exoskeleton Arm, Electric Motors, Pneumatic Cylinders, Interaction Force, Patient, Harmonic Motion, Mechanical Impedance, Experiments, Simulations. Abstract: A new construction of upper limbs exoskeleton with hybrid drive was studied in this work. The paper presents mechanical structure and actuation of exoskeleton with hybrid drive including pneumatic cylinders and electric motors. In order to evaluate the transparency and safety, the capabilities of the exoskeleton in passive mode of interaction was estimated. A model of the interaction force between the patient and the exoskeleton arm in passive mode was built. The model was based on harmonious movements imposed in one joint of the exoskeleton arm. Experiments and simulations were performed to assess the interaction force between the patient and the exoskeleton because of the mechanical impedance of the device. The force of interaction was obtained from passive forces, such as inertial, frictional and gravitational forces, as well as from the elasticity of the pneumatics. The patient-initiated harmonic motion was studied in two cases- without pressure in the chambers and with pressure for gravity compensation. The results where demonstrated graphically. Conclusions where made about the behavior of the exoskeleton in the passive mode of interaction. 1 INTRODUCTION Robotic rehabilitation using exoskeletons is an alternative to conventional manual therapy to improve motor function in post-stroke patients (Manna, 2018). The rehabilitation exoskeleton (Jarrasse, 2014) should be able to create a great force for assisting and directing the patient's hand in the early stages of recovery, as well as following the human hand without opposition or being able to react to any movement made by the patient in the full stage of recovery. In the control design of the rehabilitation exoskeleton in general, two "extreme" ideal regimens can be defined, covering the entire spectrum of therapeutic interventions: "robot in charge" and "patient in charge" (Veneman, 2006). In the "robot in charge" regime, it is important that the robot has enough strength and power to realize the desired movement with a relatively high impedance. In a "patient in charge" it is important that the forces of interaction between the exoskeleton and the patient a https://orcid.org/0000-0002-2312-5725 b https://orcid.org/0000-0001-5501-7668 c https://orcid.org/0000-0001-7809-3540 d https://orcid.org/0000-0001-5051-4411 are low; in other words, the perceived impedance of the robot should be low. The main feature here is transparency. There are two main approaches to reducing the mechanical impedance of the rehabilitation exoskeletons and to ensure security and transparency in interaction: active and passive. Electric motors, pneumatic, hydraulic and other active drives are used to reducing the impedance and to control the contact force through an active approach. The active approach is based on sensors and algorithms for motor control. There are two methods to control the contact force: direct and indirect. In the direct approach, the controller regulates the force with a control loop and using force feedback of the measurement and desired value of the force (Ansarieshlaghi, 2019). Indirect force control methods are known as impedance or admittance (Hogan, 1985). Impedance controlled systems detect the deviation in position and control the force applied by the device, while admittance controlled systems 442 Chakarov, D., Veneva, I., Venev, P. and Tsveov, M. Evaluation of the Capabilities of a Hybrid Driven Exoskeleton in Passive Mode of Interaction. DOI: 10.5220/0010569004420449 In Proceedings of the 18th International Conference on Informatics in Control, Automation and Robotics (ICINCO 2021), pages 442-449 ISBN: 978-989-758-522-7 Copyright c  2021 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved