Oleg Ivlev

Soft fluidic actuators of rotary type for safe physical human-machine interaction

Safe actuators with controllable compliance are indispensable for assistive robots working in human environment and especially for rehabilitation devices physically interacting with patient. The paper introduces new patent pending soft fluidic actuators with rotary elastic chambers (REC), which produces rotational motion without any additional transmission elements. The key actuator features as inherent compliance, high back-driveability and light-weight design build a foundation for safe physical human-machine interaction, although torques of several tens of Newton-meter can be generated. Due to their compact design the REC-actuators demonstrate better integration capabilities into complex kinematic structures than conventional fluidic muscles of linear type. The actuator compliance can be varied by pressure regulation in antagonistic acting chambers, which makes soft fluidic actuators very suitable for making the transition from continuous passive motion to active (assistive) behaviour during the therapy depending on a patient activity. Conceptual design of modular compact assistive motion therapy devices based on new “slim-line” REC-actuators is presented.

MODULAR MULTI-SENSORY FLUIDIC ACTUATOR WITH PLEATED ROTARY ELASTIC CHAMBERS

Abstract This paper describes the concept and development of a new fluidic rotary actuator with natural compliance, intended for industrial automation devices and robots working in human environment. The actuator comprises few fully integrated modules with matched mechanical, electrical and software interfaces. The core element of the actuator is newly developed fluidic motor with pleated rotary elastic chambers, which replace rigid chambers of the conventional vane motor. Compact mechatronic module in hydraulic realization is presented, while considering pneumatic realization also. Due to its modular design and inherent compliance, the actuator is particularly suitable for building complex kinematic structures, as for example soft robotic arms.

Assistive control of motion therapy devices based on pneumatic soft-actuators with rotary elastic chambers

Robot assisted motion therapy attains increasingly importance and acceptance especially in neurorehabilitation after stroke or spinal injury, but also in orthopedic rehabilitation and surgical interventions. Several studies have shown that a patient-cooperative (assistive) motion therapy, which activates remaining muscle strength and so optimizes recovery, will cause a much higher effectiveness compared to commonly used continuous passive motion (CPM) machines with pre-programmed trajectories (motion profiles). This article describes an assistive control concept developed for orthopedic rehabilitation based on inherent compliant (soft) actuators. Control concept takes into acccount specific properties of physiotherapists behavior during treatment. The patient will be supported and at the same time encouraged to generate own muscular strength to perform desired movement. Concept has been implemented for two prototypes of motion therapy devices (MTD) for knee and shoulder motion therapy. The first prototype (Knee-MTD) has been extensively tested with healthy persons and now is being tested in the Clinic for Orthopaedics and Trauma Surgery of Klinikum Stuttgart to prove concept in real-life conditions.

Precise position and trajectory control of pneumatic soft-actuators for assistance robots and motion therapy devices

The goal of this work is the development and performance analysis of control algorithms for new soft fluidic actuators with rotary elastic chambers (REC-actuators). Due to their inherent compliancy these actuators fulfill the requisites for building intrinsically safe mechanisms as assistance robots and motion therapy devices, working in direct physical contact with humans. Besides the difficulties common for control design of pneumatic systems, these actuators itself posses several nonlinear characteristics causing specific problems in their modeling and control. In this work the decentralized joint control scheme is implemented, where the position controller has a cascade structure with a non-linear model based pressure control in the inner loop. Two different position control approaches, which require minimal information on the dynamics of the actuator mechanical subsystem, were investigated and tested: sliding mode control with time delay estimation as well as a fuzzy control with parameter optimization based on genetic algorithms.

Modeling and Control of Fluidic Robotic Joints with natural compliance

This paper reports on basic properties, dynamic modeling, pressure and position control of a newly developed fluidic actuator with rotary elastic chambers (REC-actuator), intended for robots working in human environment. This actuator with natural compliance can be operated by gas or oil. Pressure control of the actuator in pneumatic realization is designed using fast on-off valves, suitable for lightweight robotic joints. A phenomenological model of the actuator is considered, in which spring, damper and torque generating element are connected in parallel. The joint stiffness and damping as functions of pressures in the actuator chambers are identified in free oscillations experiments at constant pressures. The torque-generating element is further identified in a separate series of step responses experiments, using thereby previously obtained stiffness and damping. A sliding mode control law is applied for the position control of the naturally compliant actuator.

Simulation tool for kinematic configuration control technology for dexterous robots

A simulation tool for designing and testing control devices for advanced robots with an arbitrary number of redundant joints is presented. The novel real-time suitable control technology, called kinematic configuration control, bases on a new approach of resolving redundancy. For redundant manipulators with practical relevant regular kinematic chains, the approach allows to obtain a closed-form solution of the inverse kinematics, as for common nonredundant industrial robots. These offline evaluated symbolic inverse functions need low online computing power. Therefore also controllers for dexterous robots with high degree of redundancy can be implemented on low-cost consumer computer. The described PC-based simulator supports the design of this kind of controller. During a simulation process, the algorithm-specified parameters of inverse functions are optimized. The control algorithm is formed as a separate controller module. After verification it can be effortlessly transferred into a real robot control device.

Adaptive assistive control of a soft elbow trainer with self-alignment using pneumatic bending joint

For safe and effective robot-assisted rehabilitation, natural inherent compliance and self-alignment of rehabilitation devices completed with assistive behavior are assumed to be the essential properties. To provide required human joint stability each joint can be separately supported using exoskeleton-like devices. However, the necessity of exact adjustment to the individual extremity is very time-consuming for physiotherapists and strongly reduces the effective treatment time. In this paper a soft elbow trainer based on pneumatic bending joint using skewed rotary elastic chambers (sREC) is presented as first specific solution. This shaftless actuator is placed under the elbow joint and allows for implicit self-alignment to the polycentric movement of human joint axis without elaborate adjustments. Position estimation is performed using two accurate inertial measurements units (IMUs) and four less accurate but robust cost-effective resistive bend sensors (flex sensors). Sensor fusion of flex sensor and IMU signals is used to obtain a robust control feedback. An artificial neural network (ANN) is applied to combine flex sensor signals. The adaptive assistive controller learns online using dynamic model function approximation and takes into account the patients behavior, effort and abilities while maximizing the patients voluntary effort. Practical tests with healthy subjects confirm the effectiveness of the controller.

Human-robot-interaction control for orthoses with pneumatic soft-actuators — Concept and initial trails

The purpose of this paper is to present a concept of human-robot-interaction control for robots with compliant pneumatic soft-actuators which are directly attached to the human body. Backdrivability of this type of actuators is beneficial for comfort and safety and they are well suitable to design rehabilitation robots for training of activities of daily living (ADL). The concept is verified with an application example of sit-to-stand tasks taking conventional treatment in neurology as reference. The focus is on stroke patients with a target group suffering from hemiplegia and paralysis in one half of the body. A 2 DOF exoskeleton robot was used as testbed to implement the control concept for supporting rising based on a master-slave position control such that movements from the fit leg are transferred to the affected leg. Furthermore the wearer of the robot has the possibility to adjust support for stabilizing the knee joint manually. Preliminary results are presented.

Assistive acting movement therapy devices with pneumatic rotary-type soft actuators.

Abstract Inherent compliance and assistive behavior are assumed to be essential properties for safe human-robot interaction. Rehabilitation robots demand the highest standards in this respect because the machine interacts directly with weak persons who are often sensitive to pain. Using novel soft fluidic actuators with rotary elastic chambers (REC actuators), compact, lightweight, and cost-effective therapeutic devices can be developed. This article describes modular design and control strategies for new assistive acting robotic devices for upper and lower extremities. Due to the inherent compliance and natural back-drivability of pneumatic REC actuators, these movement therapy devices provide gentle treatment, whereby the interaction forces between humans and the therapy device are estimated without the use of expensive force/torque sensors. An active model-based gravity compensation based on separated models of the robot and of the individual patient’s extremity provides the basis for effective assistive control. The utilization of pneumatic actuators demands a special safety concept, which is merged with control algorithms to provide a sufficient level of safeness and to catch any possible system errors and/or emergency situations. A self-explanatory user interface allows for easy, intuitive handling. Prototypes are very comfortable for use due to several control routines that work in the background. Assistive devices have been tested extensively with several healthy persons; the knee/hip movement therapy device is now under clinical trials at the Clinic for Orthopaedics and Trauma Surgery at the Klinikum Stuttgart.

Adaptive model-based assistive control for pneumatic direct driven soft rehabilitation robots

Assistive behavior and inherent compliance are assumed to be the essential properties for effective robot-assisted therapy in neurological as well as in orthopedic rehabilitation. This paper presents two adaptive model-based assistive controllers for pneumatic direct driven soft rehabilitation robots that are based on separated models of the soft-robot and the patients extremity, in order to take into account the individual patients behavior, effort and ability during control, what is assumed to be essential to relearn lost motor functions in neurological and facilitate muscle reconstruction in orthopedic rehabilitation. The high inherent compliance of soft-actuators allows for a general human-robot interaction and provides the base for effective and dependable assistive control. An inverse model of the soft-robot with estimated parameters is used to achieve robot transparency during treatment and inverse adaptive models of the individual patients extremity allow the controllers to learn on-line the individual patients behavior and effort and react in a way that assist the patient only as much as needed. The effectiveness of the controllers is evaluated with unimpaired subjects using a first prototype of a soft-robot for elbow training. Advantages and disadvantages of both controllers are analyzed and discussed.