Abstract
Therapeutic exercises play an important role in physical therapy and rehabilitation. The use of robots has been increasing day by day in the practice of therapeutic exercises. This study aims to design and control a novel robotic platform named DIAGNOBOT for diagnosis and treatment (therapeutic exercise). It has three 1-degree-of-freedom robotic manipulators and a single grasping force measurement unit. It is able to perform flexion–extension and ulnar–radial deviation movements for the wrist and pronation–supination movement for the forearm. The platform has a modular and compact structure and is capable of treating two patients concurrently. In order to control the DIAGNOBOT, an impedance control–based controller was developed for force control, which was required for the exercises, as well as a proportional–integral–derivative controller for position control. To model the resistive exercise, an angle-dependent impedance control method different from traditional methods has been proposed. Experiments were made on five healthy subjects and it has been demonstrated that the proposed robotic platform and its controller can perform therapeutic exercises.
Introduction
Rehabilitation is a treatment process aimed at helping people with physical or anatomical disabilities. These disabilities might be congenital or may have occurred due to an accident, injury, or illness, and this treatment process aims to help such people achieve the highest possible level of functionality in the medical, vocational, and social spheres. Rehabilitation allows disabled people to participate in life at the highest possible level.1 Due to the increasing world population, the need for rehabilitation is also increasing. Individuals with several limbs injured due to age, war, traffic or work-related accidents, or chronic diseases need rehabilitation to achieve full or partial recovery. A wide range of medical methods and treatments have been developed to refunctionalize these limbs, improve their range of motion (ROM) and muscle strength. Therapeutic exercises, one of these methods, play a crucial role in the process of restoring refunctionality for disabled limbs. Therapeutic exercises have two types: passive and active. These exercises can be performed by a physiotherapist or the patient himself.
There are several difficulties and limitations involved in the rehabilitation process, such as an inadequate number of doctors and physiotherapists per patient in highly populated countries, the difficulties suffered by bedridden and aged patients in reaching hospitals, the cost of the rehabilitation process, the duration of the treatment, and keeping a log and following up on the treatment process. According to a report by the Turkish Ministry of Health, the number of physiotherapists per 100.000 people in Turkey is four.2 The highest number of physiotherapists is in Finland, with 202 physiotherapists per 100.000 people. Because of these reasons, the number of studies on rehabilitation robotics has seen an increase over the last two decades.3
Upper limb rehabilitation robots can be classified in terms of mechanical structure, movement capacity, variety of exercises, and control methods. The existed systems can perform one or some of the following exercises: the passive, the resistive, and the active assistive. The control methods commonly used in robotic rehabilitation are as follows: conventional control approaches, such as proportional–derivative (PD) or proportional–integral–derivative (PID), torque control, admittance control, and impedance control.
The MIT-MANUS is a well-known robotic system used for upper limb rehabilitation.4 The system has 3 degrees of freedom (DOFs) and can perform the passive, the active assistive, and the resistive exercises. The control method of the system is impedance control. Reinkensmeyer et al.5 designed a 4-DOF robot, named Assisted Rehabilitation and Measurement Guide (ARM-Guide), for the rehabilitation of the shoulder and the elbow. PD position control and torque control methods were used in the system. The REHAROB was designed using a 6-DOF industrial robot.6The robot can perform passive exercises for decreasing the spasticity in the shoulder, the elbow, and the forearm. In their study, Fraile et al.7 designed a 2-DOF planar robotic platform, called E2Rebot, for upper limb rehabilitation in patients with neuromotor disability caused by a stroke. Besides these studies, there are many other examples of rehabilitation robots.8–13
A 6-DOF exoskeleton robot was developed by Nef and Riener14 for the rehabilitation of the elbow and the shoulder. The robot can perform passive- and active-assisted exercises. The control method of the system is admittance and impedance control. The use of such exoskeleton robots in rehabilitation is becoming more and more commonplace, and there are a big number of studies cited in the literature.15–29
As seen in the literature, many robots have been developed for the rehabilitation. These robots have some limitations. These limitations are DOF, independency of operating of axes, grasping of end-effector (handle), and inability for diagnosis. First, robotic manipulators have one or more DOFs in a single structure. This leads to limitations both in the control of the system and in the force and torque measurements to be made for each axis for diagnosis. Second, the failure of one of the axis also affects other axes. These robots allow for the treatment of only one patient at the same time. Third, in the previous designs, the patients grasp the end-effector. This way is not effective in stroke patients who cannot grasp. Finally, existed designs are not suitable for diagnosis.
To overcome these limitations, a novel robotic platform has been developed in this study. The developed system called DIAGNOBOT consists of three 1-DOF robotic manipulators and a single grasping force measurement unit. The most important feature of this system is that it can perform diagnosis and treatment simultaneously. For this purpose, it is equipped with sensors and actuators developed in a suitable mechanical structure. The force and torque sensors are located in the direction of movement. The robot manipulators for each movement were placed on a rotating table. Each unit can easily be removed and installed. It ensures that the robotic system is modular and configurable. Because the units are independent of each other, it allows for the treatment of two patients at the same time. Thanks to this design, the failure of a unit does not affect other units. The robot manipulators are designed according to stroke patients and they do not need to grasp manipulators (handles). The developed system can perform flexion–extension and ulnar–radial deviation movements for the wrist, and pronation–supination movement for the forearm. It can perform the passive, isometric, isotonic, and resistive therapeutic exercises. DIAGNOBOT controller has a force-based impedance control structure for the isotonic exercise. For variable resistive exercises, a novel impedance–based control method has been developed. In this method, the force on the end-effector changes depends on the joint angle. Therefore, this new control approximation is called the angle-dependent impedance control. This method’s efficiency has been confirmed through experiments made with five healthy subjects. On the other hand, PID control was used for the passive exercise.
There are two contributions to the literature in this study. The former is the unique design of the robotic platform both diagnosis and treatment for upper limb rehabilitation, the latter is the development of a controller based on angle-dependent impedance control to model resistive exercises. An explanatory video about the developed system can be reached in the link.30
This article is organized as follows: the theory of upper limb rehabilitation is specified first, followed by the mechanical design, electronics hardware, strength and limitations, the dynamics, and the control and operation, respectively. Finally, the results and the conclusion are given.
Theory of upper limb rehabilitation
Therapeutic exercises are performed to improve the strength, endurance, coordination, speed, and skills of the limbs. They can be passive or active and can be performed manually or by an assistive device. Therapeutic exercises are considered as one of the important stages of the physical therapy and rehabilitation. In this study, the therapeutic exercises are performed for the rehabilitation of the wrist and the forearm.
The developed rehabilitation robot can perform flexion–extension and ulnar–radial deviation movements for the wrist, and pronation–supination movements for the forearm. The definitions of these movements are given in Figure 1 and explained below.
Figure 1. The movements of the wrist and the forearm.
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TBI Rehabilitation 