André Wilkening

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.

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.

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.

Safety and handling concept for assistive robotic devices with pneumatic rotary soft-actuators

Compliance and assistive behavior are essential properties for safe physical human-robot interaction (HRI), an illustrative example for which is robot aided motion therapy. These requirements can be easily fulfilled using inherent compliant and back-drivable (i.e. soft) actuators. This paper describes a fully functional prototype for assistive robotic knee MTD with novel inherent compliant (soft) fluidic actuators of rotary type, which has been developed for orthopedic rehabilitation purposes. Assistive acting motion therapy devices (MTD) are mainly used for neurologic treatment until now, but become increasingly important for orthopedic rehabilitation as well. Device capabilities provide human-like treatment and allow individual adjustable assistance to accomplish desired motions. Utilization of pneumatic soft-actuators demands a special safety concept which is merged with control algorithms to provide sufficient safeness and to catch any possible system errors and sudden emergency situations. A self descriptive user interface allows easy intuitive handling and the prototype can be used very comfortable due to several imperceptible working routines in the background. The same safety and handling concept is used for assistive robotic shoulder MTD, which is currently being developed.

Compact Assistive Rehabilitation Devices– Concept and Preliminary Function Test

Conceptual design of compact light-weight devices for lower extremity motion therapy and rehabilitation is presented. The core of these devices are new inherent complaint (soft) fluidic actuators of rotary type, which generally provide safe and gentle treatment. The actuator compliance can be varied by pressure regulation, which makes soft fluidic actuators very suitable for making the transition from continuous passive motion to active (assistive) behavior during the therapy depending on patient activity. The assistive behavior can be realized without force measurements by means of expensive sensors.

Estimation of mass parameters for cooperative human and soft-robots as basis for assistive control of rehabilitation devices

For safe human-robot interaction, the robots, especially exoskeletons, should be transparent for the user, in a way that the user does not feel their weight. In robot-assisted orthopedic rehabilitation, where patients are often sensitive to pain and often not able to lift affected limbs by themselves, this requirement is of crucial importance. To allow patients directly after surgical intervention to participate actively, not only the weight of the robot, but also the weight of the patients extremity must be compensated. Several assistive acting soft robotic rehabilitation devices have been developed for upper and lower extremities based on pneumatic actuators with rotary elastic chambers (REC-actuators), well suitable for human-robot interaction because of natural inherent compliance. The essential basis for developed adaptive model-based assistive control strategies, in order to provide robot transparency as well as take into account patients behavior, effort and abilities, and support patients with high voluntary effort, are separated models of soft-robots and of individual patients extremities. This paper presents an approach to estimate unknown mass parameters of soft robotic rehabilitation devices as well as of individual humans extremities, using a minimal number of experimental measurements as well as specific characteristics of pneumatic REC-actuators without the use of torque sensors. An experimental study shows the influence of using the models based on estimated parameters during control, using a four DoF soft-robot as well as a prototype of an assistive elbow trainer with an unimpaired subject, as first part of a upper extremity rehabilitation robot.

Experimental and Simulation-Based Investigation of Polycentric Motion of an Inherent Compliant Pneumatic Bending Actuator with Skewed Rotary Elastic Chambers

To offer a functionality that could not be found in traditional rigid robots, compliant actuators are in development worldwide for a variety of applications and especially for human–robot interaction. Pneumatic bending actuators are a special kind of such actuators. Due to the absence of fixed mechanical axes and their soft behavior, these actuators generally possess a polycentric motion ability. This can be very useful to provide an implicit self-alignment to human joint axes in exoskeleton-like rehabilitation devices. As a possible realization, a novel bending actuator (BA) was developed using patented pneumatic skewed rotary elastic chambers (sREC). To analyze the actuator self-alignment properties, knowledge about the motion of this bending actuator type, the so-called skewed rotary elastic chambers bending actuator (sRECBA), is of high interest and this paper presents experimental and simulation-based kinematic investigations. First, to describe actuator motion, the finite helical axes (FHA) of basic actuator elements are determined using a three-dimensional (3D) camera system. Afterwards, a simplified two-dimensional (2D) kinematic simulation model based on a four-bar linkage was developed and the motion was compared to the experimental data by calculating the instantaneous center of rotation (ICR). The equivalent kinematic model of the sRECBA was realized using a series of four-bar linkages and the resulting ICR was analyzed in simulation. Finally, the FHA of the sRECBA were determined and analyzed for three different specific motions. The results show that the actuator’s FHA adapt to different motions performed and it can be assumed that implicit self-alignment to the polycentric motion of the human joint axis will be provided.

Estimation of Physical Human-Robot Interaction Using Cost-Effective Pneumatic Padding

The idea to use a cost-effective pneumatic padding for sensing of physical interaction between a user and wearable rehabilitation robots is not new, but until now there has not been any practical relevant realization. In this paper, we present a novel method to estimate physical human-robot interaction using a pneumatic padding based on artificial neural networks (ANNs). This estimation can serve as rough indicator of applied forces/torques by the user and can be applied for visual feedback about the user’s participation or as additional information for interaction controllers. Unlike common mostly very expensive 6-axis force/torque sensors (FTS), the proposed sensor system can be easily integrated in the design of physical human-robot interfaces of rehabilitation robots and adapts itself to the shape of the individual patient’s extremity by pressure changing in pneumatic chambers, in order to provide a safe physical interaction with high user’s comfort. This paper describes a concept of using ANNs for estimation of interaction forces/torques based on pressure variations of eight customized air-pad chambers. The ANNs were trained one-time offline using signals of a high precision FTS which is also used as reference sensor for experimental validation. Experiments with three different subjects confirm the functionality of the concept and the estimation algorithm.

Adaptive position control of fluidic soft-robots working with unknown loads

The compliance of robot structure is essential to provide safety if robots are working in the direct contact with humans. Soft-actuators possess natural inherent compliance but they are characterized with highly non-linear dynamics making accurate control a challenging task. This paper presents the robust and adaptive position control of soft-robots based on pneumatic actuators with rotary elastic chambers (REC-actuators). Previous work shows that accurate control of soft-robots is possible if load parameters are known and taken into account in quasi-static model of soft-robots, that is used as feed-forward signal. This paper demonstrates that adaptation of the robot model provides flexibility and robustness when soft-robots deal with unknown loads. It is shown that due to adaptation the load parameters are not needed to be changed in the quasi-static robot model. The performance of the adaptive controller is proven in simulation and in experiments using firstly a simple 1 degree of freedom (DoF) and then a complex 6 DoF robot structure.