An Overview of Rehabilitation Robots and their Application

Abstract

In the community health system, non-pharmacological treatments are at the forefront of countries’ treatment. One of these treatments is rehabilitation. Rehabilitation is considered a very broad scientific field in the set of health and medical services and helps people recover after suffering from problems such as stroke, spinal cord injuries, orthopedic surgery, concussions, burns, hearing loss, central auditory processing disorder, balance problems, overcome their problem as much as possible and regain their previous functional independence. This process is expensive and requires a lot of time and patience. There are many exercise machines for rehabilitation purposes. These types of machines are not flexible during operation, and this lack of flexibility destroys their ability to face unwanted conditions during physiotherapy. Therefore, the necessity of using mechatronic technologies in the field of rehabilitation is clearly evident. In this chapter, we will first give an overview of a number of research projects carried out in the field of rehabilitation robots (mainly lower body) and, since our main focus is more on the optimal control of the intelligent system (mechatronics), in the continuation of the strategies we describe different controls applied to rehabilitation robots and examine their strengths and weaknesses.

1. Introduction

The human movement system since birth is an extremely harmonic, regulated and purposeful system that has always attracted the attention of scientists interested in physiotherapy until 1945 due to the absence of physiotherapists and the existence of only physiotherapy technicians and activities in the rehabilitation and rehabilitation departments, of a part of It has been rehabilitation, but after 1945 and the emergence of the modern physiotherapist, it included treatment and rehabilitation, and after 2000, with professional doctorate titles, physiotherapy included prevention, treatment and rehabilitation.

In the last decade, the introduction and use of robotic technologies for the purpose of rehabilitation has turned from concept to reality. In general, rehabilitation robots are classified on three basis: one is based on the therapeutic field, the second is based on how to interact with the patient, and the third is based on the purpose of use in the therapeutic field. Rehabilitation robots are divided into upper and lower body groups. Upper body robots are generally used to restore the mobility of the arm or forearm or fingers. On the other hand, lower body robots have been used to restore the mobility of the knee, thigh, hip, ankle, and foot. The robots that are made for knee treatment are also lower body robots, but the general purpose of lower body robots is mostly a robot that must maintain the balance of the patient’s weight while working and the patient while working with it, is standing. The difference between upper body and lower body rehabilitation is that the weight of the body is on the lower body, and it plays a major role in losing the balance of the lower body. In lower body robots where both legs work together, coordination is very important. Upper-body robots benefit from virtual reality technology for their work, while this issue is rarely seen for lower-body robots [1, 2].

In another classification, rehabilitation robots are divided into two groups: external skeleton and final effector. The sacral skeleton is a robot that is made in the shape of one of the body parts and is connected to the disabled part at several points and moves it along with it. The advantage of using the exoskeleton is that it always supports the disabled member and is more useful in obtaining movement coordination. Controlling these robots is more difficult than other types of robots due to the number of connections and the need to coordinate them with each other. In contrast to the external skeleton, the final effector must be mentioned, which is connected to the disabled member at only one point. The final effector has a much higher force interaction rate than the external skeleton, and the patient feels more free while working with it.

In the last classification, rehabilitation robots are divided into two groups: collaborators and therapists. Collaborative robots help the patient to do the tasks of daily life and there is no therapeutic motivation. But therapeutic robots are used to increase the patient’s movement ability.

2. Completed projects in the field of rehabilitation robots

The designs that have been developed so far in the world for the rehabilitation of the lower limbs of physically disabled patients can be divided into four general categories in terms of how the mechanism works:

2.1 First category: body weight support system

There are mechanisms in which a body weight support system is used while walking. The structure of this system is shown in Figure 1.

Figure 1.

Walking on the ground using a body weight support system.

By conducting a series of tests on disabled patients using this system, the result has been that the ability to walk has been greatly improved compared to the old methods. A test sample was conducted at the National Rehabilitation Hospital of the Netherlands in 2002 on sixty seriously injured patients. In this way, these sixty people were randomly divided into two groups. For the first group of old physiotherapy methods and the second group of new physiotherapy system (Figure 1) called ZeroG was used. Both groups were treated for 2 hours a day, 5 days a week, for 14 weeks, and after this period, the improvement of walking on different and even heterogeneous surfaces was visible for the second group much more than the first group [3, 4, 5, 6].

2.2 Second category: treadmill

There are mechanisms in which treadmills are used. These devices are only able to simulate human walking on smooth surfaces. Based on the conducted research, walking on a treadmill alone cannot have a great effect on the rehabilitation of stroke or spinal cord injury patients; Because it does not have the ability to simulate many situations, such as climbing the stairs, rotating the ankle joint, etc. (these capabilities are available in the first type of systems). Accordingly, in addition to the treadmill, other side mechanisms are also used in these designs [7, 8]. One of the most famous designs in this field is the Lokomat robotic set, which is shown in Figure 2.

Figure 2.

Lokomat robotic assembly.

This device is made by the Swiss Hocoma® company and is commercially available on the market today. In this design, the movement of each of the hip, knee and ankle joints is controlled by a separate electric actuator. Also, a degree of freedom for the movement of the upper body in the vertical direction is considered, for which the necessary force is provided by a pneumatic operator, and the amount of this force can be adjusted by an active control system. Also, the device includes force and position sensors in several places, as well as a display for simulating virtual environments. The amount of interaction forces is also shown to the patient by the displays [2].

2.3 The third category: exoskeleton

There are mechanisms in which external skeletonization is used. The skeleton is connected to the patient’s body from several points and is usually made of several pneumatic actuators that coordinately help the disabled person’s muscles and create natural movements. One of these simple designs is a device called CPMs(Continue Passive Motions) and is shown in Figure 3. This device is used in most pharmaceutical centers for the treatment of disabled patients and rehabilitation purposes. The concept of CPM was first introduced in the 1970s by Salter and Simmonds.

Figure 3.

CPM for lower limbs.

In some cases, the CPM device is not suitable for the physiotherapy treatment process. During rehabilitation, patients sometimes move their leg beyond expected limits as a reaction to an operation, quite by accident. Old machines such as CPM are not able to respond in these conditions. If a reflex causes the patient’s leg to move beyond the expected limit (the range of motion of the machine), an inappropriate load is produced and can damage the patient’s muscles or tendon tissues [9].

Figure 3 shows the plan of the University of Michigan researchers. This design is used to rehabilitate muscles effective in ankle movement, which is made of two pneumatic actuators. The noteworthy point in this plan is the use of EMG(Electromyography) signals to help stimulate the patient’s muscles along with the mechanical system [1, 2, 6].

Another type of these designs is RGO, which was developed by a research group at Stanford University, England, and is shown in Figure 4. In this mechanism, the movement of each leg has 5 degrees of freedom, of which three degrees of freedom are related to the hip area, one degree of freedom for knee movement and one degree of freedom for wrist movement. The accuracy of changing locations in this system is 1% and its bandwidth is 5 Hz.

Figure 4.

Image of RGO.

The ALEX robotic set is another type of these designs that was made at the University of Delaware. Figure 5 shows the image and components of this device [8]. In addition to the degrees of freedom related to movement in the sagittal plane, this device has the ability to create horizontal movement in the frontal plane, the ability to rotate the upper body around the vertical axis, and the ability to create adduction and abduction movements in the hip joint [6].

Figure 5.

Components of ALEX rehabilitation device: A: Vertical displacement mechanism; B: Four-bar mechanism for vertical movement; C: Sliding mechanism for horizontal movement in the frontal plane; D: Hinged connection to create abduction and adduction movements of the leg; E: Hip joint to create thigh movement in the sagittal plane; F: Treadmill; G: Hinged connection for turning around the vertical axis; H: Person support from the back, I: Upper body support harnesses, J: Thigh support, K: Knee joint, L: Foot entry point.

Another one of these plans is the LOPES robotic set, which is shown in Figure 6. This robot was made at the University of Twente in the Netherlands and has the ability to move the whole body in front-back and left-right directions. The weight is passively restrained by a four-bar mechanism.

Figure 6.

LOPES robotic set.

2.4 The fourth category: moving pages

There are mechanisms in which moving plates are used under the soles of the patient’s feet in order to create the desired movement. In these mechanisms, by planning the movement of the moving plate, the whole leg or a part of it is forced to move or they are helped in creating desired movements.

The most important projects in this field are as follows:

1. Figure 7 shows the plan of Rutgers University researchers. This mechanism is used to rehabilitate stroke patients who have disabilities in the ankle area. In this design, a parallel mechanism is used to create different movements. In addition to using the virtual reality environment with the help of a computer, the quality of the rehabilitation process has been improved [10].

1. The research group of Rutgers University has presented a plan in which two parallel mechanisms are used under both legs of the patient, with the difference that a person uses this robotic set while standing. This robot is called Mobility Simulator, and it is shown in Figure 8. In this design, a part of the person’s weight is kept by straps tied to him from above.

Figure 7.

Rutgers university plan for rehabilitation of ankle muscles.

Figure 8.

A picture of the mobility simulator robot.

In the following, we will have an overview of some other completed projects in the field of rehabilitation robots.

In 1998, a system with two robots was introduced, each of which included 2 degrees of freedom. This system was suitable for minor unpredictable movements (low range of motion and lower limbs) and was also used to predict the parameters of human body parts. In 1990, a robotic system for rehabilitation with more unwanted postures (more range of motion) was developed. In 1995, a collaborative arm rehabilitation system was introduced. Another system for upper limb rehabilitation that included 5 degrees of freedom robotic arm was developed in 1997 under the name of the MULOS project. In 1998, a system named MIT-MANUS was presented, which included a clinical robot with a neurological rehabilitation system. This system included a robot with multiple degrees of freedom and suitable for injured and traumatic patients. Also, in 1990, another system using the Puma 240 robot was introduced, which was used for active and passive rehabilitation of the upper limbs. In 1999, a 3-degree-of-freedom pneumatic system was developed for rehabilitation, which uses PD and impedance controllers. In 2000, another work for rehabilitation was the REHABROB project, which involved two industrial robots. The main idea is based on the required force and position provided by sensors placed on different parts of the patient’s body during the rehabilitation process. Then, the industrial robots repeat the same procedure based on the information collected from the sensors and the requested force and position. These cases and other projects done in this field can be found in Refs. [9, 10, 11].

3. Parallel robots

Considering that the motivation of robotics science and technology is the development of mechanical systems in which robots do the work instead of humans, it is almost obvious that most of the attention will be directed towards open series rings as a robot arm. Such robotic arms have advantages such as a large working space and high maneuverability, similar to a human arm, but usually due to a structure similar to a sniper’s arrow, they have a small load carrying capacity. As a result, on the one hand, they suffer a lot of rise and, on the other hand, they vibrate at high speeds. Also, as mentioned, they have a large working space, but they do not have the ability to accurately position themselves. In short, open arms have the advantages and disadvantages of the human arm. Therefore, in practice, when the ability to carry heavy loads, good dynamic efficiency and accurate positioning are desired, it is better to use a method other than traditional series arms. In general, it can be concluded that robot arms whose final actuators are connected to the ground through closed rings with parallel actuators have higher rigidity and accuracy [3]. For this reason and because of the controllable degrees of freedom, parallel mechanisms have been given more attention for some applications, and since 1980, a relatively large amount of research has been done in this field. One of these mechanisms is the Stewart mechanism, which we will describe below:

3.1 Stewart mechanism

This six-degree-of-freedom mechanism was first used by D. Stewart in 1965 in a flight simulator. The Stewart mechanism used in 1965 consisted of a triangular plate supported by spherical joints on three legs of variable length. This mechanism also had angular height gauges that were connected to the ground by two simple joints. After that, the mechanism proposed by Goff, which was used in the car tire tester and used six linear operators, turned Stewart’s mechanism into a completely parallel mechanism. Then Hunt proposed in 1978 that parallel mechanisms such as the Stewart mechanism, which is used in flight simulations, could be used as a robotic arm. These mechanisms have special advantages, such as higher rigidity and more accurate positioning than conventional robots [4].

Today, the Stewart mechanism consists of two solid bodies (one base and the other moving plate) which are connected through six linear actuators. These operators are connected to the plates in two ways. One is to be connected to the plates from both sides with spherical joints, and the other is to be connected to the plates from one side connected to plates with spherical joints and joints the other hand with universal, joint. The first mode is called 6-SPS and the second mode is called 6-UPS. In cases where there is no emphasis on a specific type, any of the above situations can be considered. Of course, we note that these mechanisms have a similar dynamic behavior and the only difference is that the SPS mode has six additional degrees of freedom related to the rotation of the actuators around its axis, which does not affect the overall performance of the mechanism [4, 5]. Due to their closed nature, parallel mechanisms also have a number of inactive joints, which makes all the joints of this mechanism not controllable independently [1, 2, 6]. In fact, if the mechanism does not have additional stimulation, the number of independently controlled joints is equal to the number of degrees of freedom of the moving plate of the mechanism (Figure 9).

Figure 9.

Parallel robot mechanism.

Flight simulators can be mentioned among the oldest applications of Stewart robots. Examples of its applications are shown in the followingFigures 10–14.

Figure 10.

Parallel robot mechanism.

Figure 11.

Stewart flight simulator.

Figure 12.

Airbus A320 flight simulator.

Figure 13.

The largest driving simulator built at the University of Iowa.

Figure 14.

KAIST and Motek simulators.

The following Figures 15–18 show other examples of applications of parallel robots in industries:

Figure 15.

Paris positioning robot.

Figure 16.

An example of the industrial application of the F-200i robot in maintaining and transporting the cylinder block.

Figure 17.

PH1 and PHEX1 vibration isolators in CSA. engineering group.

Figure 18.

Mars robot with 6-ups structure as a surgeon’s help.

4. Conclusions

Robotic rehabilitation is a field of research dedicated to understanding the enhancement of rehabilitation through the use of robotic physiotherapy devices. Robotic rehabilitation involves the development of robotic devices to assist with various sensory and motor functions such as arms, hands, feet, ankles). Advancement and development of various programs to help therapeutic sports and evaluate the performance of the motor system of the patient (patient movement, where robots are used instead of aids as a sensory aid for treatment) Rehabilitation using robots is more tolerable for the patient, and it has also been determined that it is an effective treatment method for patients who suffer from movement problems, such as people with a stroke. Therefore, in this chapter, lower trunk rehabilitation robots and their use in limb rehabilitation will be examined. We discussed the patient’s lower body in four categories: 1- Maintaining body weight, 2- Treadmill, exoskeleton (external skeleton) and 4- Moving plate. The results of investigations and research show that the structure of parallel robots whose final executor through Closed loops are connected to the ground with parallel operators and have higher precision and accuracy for rehabilitation applications.