A 4-DOF Workspace Lower Limb Rehabilitation Robot: Mechanism Design, Human Joint Analysis and Trajectory Planning

Round 1

Reviewer 1 Report

Authors clarify the concept of circonduction as combination between F/E and A/A

They compared the proposed device with other robot for lower limb rehabilitation and they stressed the possibility to start the rehabilitation very early after stroke when the patients show flaccidity and he/she is not able yet to stay in standing position as the lack of trunk control.

The low cost could be an add value

Author Response

Dear Reviewer:

Thank you for your comments and suggestions. They help us a lot to improve the quality of this paper. 

The paper has been modified carefully. 

Reviewer 2 Report

1. Please enter the formal name of the DOF. Degrees of freedom? Please enter the correct DOF name in the first sentence. Please do not abbreviate in only first sentence.

2. In Figure 1, 2 and 3, the authors explain the mechanical design of this device, but I cannot understand how this device performs adduction/abduction movements of the hip joint. I can understand hip flexion extension, ankle plantar flexion and dorsiflexion. Does the Adduction/abduction motion module (Fig 1) extend inside and outside? The schema will help the reader understand.

3. Does this device support passive movement of the patient? Does The liner actuator (Fig 3) support passive movement of the patient?

4. What kind of diseases are you targeting in the future study? (what is the disease of indications?) What is your future study plan? Please state it in discussion.

5. I think that conclusion should be a little bit more concise (shorter) for the reader.

6. In the Abstract, line 8, as the author described as “guarantee the patient's joint safety”, when you implement similar experiments for patients with diseases or limited mobility, I will recommend evaluation of safety. It would be necessary to consider the safety of this device. I do not think that adverse events such as pain in the hips, knees, ankles, and severe fatigue will not happen related to this device directly. Was there pain or adverse events in healthy subjects in the prototype experiment (p13, figure 13)?

7. If you have some limitation of this study, please enter in discussion.

Author Response

Dear Reviewer:

Thank you for your comments and suggestions. They help us a lot to improve the quality of this paper. And responses are as follow:

1. The formal name of the DOF is entered in the first sentence (Page 1 Abstract line 3).

2. The adduction/abduction movements of the hip joint is performed through the changing of the linear actuator, and Figure 6b is updated to explain this mechanism. The linear actuator is in the minimum length while the parallelogram mechanism is straight, and the adduction/abduction motion module just extends outside excepting changing the assembling position of the linear actuator (Page3 Section2 paragraph1). One leg training part could provide training for left/right legs through this design.

3. This robot provided passive training movement in the trajectory tracking experiment, and this robot supports passive training, teaching training and resistance training (Page3 Section2 paragraph1). Other functions such as VR training would be migrated from other rehabilitation devices developed by our team. Linear actuator or motor of each joint is controlled by it's amplifier, and they all make corresponding according to the upper monitor. In the trajectory tracking experiment, the linear actuator makes motions based on the preset planning trajectory.

4. The disease target is stroke in the future study, the main indication is the limb physical-motor disability. Discussion has been updated.

Rehabilitation medicine is a wide subject, and it is mainly divided into neurological rehabilitation (stroke,…) and orthopedic rehabilitation (surgery,...). There are both similarities and differences between two kinds of rehabilitations, and this device mainly targets at stroke to help patient in avoiding limb physical-motor disability. In the future, more training functions for stroke would be studied based on clinical applications.

5. Conclusion has been simplified for reading.

6. Firstly, clinical trials haven't been conducted with this device so far, and the subject in this paper is a healthy volunteer. However, because of following the doctor's advice before using other our other devices, seldom pain or fatigue was happened to patient in robot-assisted therapy. In adverse events, the solution to muscular spasticity is under researched. The plan is stopping the training and warning to the doctor while the interaction force from the pedal sensor is abnormal.

7. Discussion has been updated.

In the kinematic model of the lower limb, the ankle joint motion is not fully considered. This issue is regarded as the main source of human joint errors. Meanwhile, the behavior of the A/A training is not very well when the leg is not straight. The little axial rotation of the leg is the main reason of this situation. These problems would be investigated in the future work.

 

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In this manuscript authors  present a prototype of  a 4-DOF spatial workspace lower limb rehabilitation robot able to provide single/multiple joint rehabilitation  training for three lower limb joints.

At the moment a lot of devices for lower limb rehabilitation training are already developed. Among them both exoskeletons and end effector devices are used for walking training on treadmill with or without body weight. Another  group of exoskeleton devices have been developed for on ground training for gait recovery.

The device described in this paper is focused on circumduction training of the hip. As for biomechanical point of view the hip joint is not able functionally perform circumduction movement as the only human joint which is able to perform a real circumduction is the shoulder. Both shoulder and hip cannot be considered as real spherical joint because the constraint due to the muscles.

Furthermore authors propose a lower limb training while the patients is seated on a wheelchair. This kind of training is not so useful for gait recovery as the trunk control, not trained in seating position, is crucial for walking recovery.

In conclusion remain unclear to me the originality of the proposed device. Actually it seems to be able to passively move the hip joint combining A/A and F/E. The only interesting factor is represented from the capability to measure kinematic parameters which often are not recorded by the other devices. This advantage is limited as the measurements are provided in seating position.

In conclusion the clinical application of the device seems to be very difficult.

I kindly request to the authors to stress this point checking the other devices available on the market and providing a comparison with to prototype proposed.  

Author Response

Cover letter

Dear Reviewer:

 

Thank you for your comments and suggestions. They help us a lot to improve the quality of this paper. And responses are as follow:

 

There are truly many exoskeletons and end effector devices used for gait training or ground training. It is very helpful to mid or late period patient which need gait training, and it could make the patient more confident. But, there are also a lot of lying/sitting training rehabilitation robots for earlier patients. A new Table 1 shows the comparison of typical rehabilitation robots. And we are in agreement with the classification of rehabilitation robots in reference 8.

 

This paper is not focused on the hip circumduction training. It might be due to writing logic. Abstract and Introduction have been modified, and the focus of this paper would be also explained again in the follow part. As for circumduction training of the hip, it is a thigh conical motion combined with the flexion/extension and the adduction/abduction. And it is confirmed by the doctor of our team that circumduction training could be useful in some situation. There are also some relative references in this paper (30,31). Circumduction training is selected to exhibit the capability of this robot; the main reason is that the circumduction training could seldom be performed by other robots. And it could also indicate the necessary of hip adduction/abduction training.

 

This robot is not used for walking recovery. Like other sitting/lying rehabilitation robots shown in Table 1, this robot is used for earlier rehabilitation. For example, stroke patients would suffer a flaccid paralysis period in early stage. In this period, they could not control their muscle. But there is a window of enhanced neuroplasticity early after stroke (reference 32); they need rehabilitation training to promote recovery in this period. Traditional method is receiving manual rehabilitation training by therapists. This kind of robot could be an alternative solution in this solution.

 

Our team has researched the lying/sitting lower rehabilitation robot for years. Based on the patient handling problem and training limitations of our series robots (reference 17 and 21), this robot is developed as a new ideal. Therefore, the focuses of this paper are the design of a 4-DOF spatial workspace rehabilitation robot, the human joint analysis method used for guaranteeing joint safety in the working method of this robot and the trajectory tracking experiment. The cost of avoiding frequent patient handling is the measurement before training, and it is easier than move a patient without standing ability in our experience.

 

The originality of this robot is adduction/abduction training of hip joint, and it’s working method could avoid frequent patient handling between the wheelchair and the rehabilitation robot. The human-robot hybrid kinematic model and human joint analysis method are also a new attempt.

 

Because of the safety of this robot, we are optimistic about the clinical application. And it is convenient to frequent using places like hospital.

 

The comparison is shown in the Table 1.

 

Thank you very much for your patience.

 

Sincerely yours,

Hongbo Wang and et.

Reviewer 2 Report

In their Manuscript “A 4-DOF spatial workspace lower limb rehabilitation robot: mechanism design, human joint analysis and trajectory planning”, the Authors propose a new device for lower limb rehabilitation. Several tools are already available, but, in the author’s opinion, the novelty of the robot is the ability to train the circumduction of the hip.  Even though the topic is interesting, some crucial lacks prevent from the publication of the study in its present form, as reported below

Main criticisms

• The design of rehabilitation robots consists of two main aspects, i.e., the mechanical design and the control strategy design. The latter is partially missing. The design of these devices cannot lack a description of the interaction control.
  • On the light of the above, what type of controller was implemented (impedance control, admittance control, etc.)?
  • What are the interaction forces?
  • Does the robot provide only a passive joint movement?
  • How does it cope with patients’ joint resistance, as in the case of muscular spasticity? In other words, what about safety?
  • How is the displacement controlled? Mean speed is reported, but how about speed shape? Is it smooth?
• Moreover, what about its feasibility? The robot should also be tested in a small number of patients and the feasibility investigated.

Other criticisms

• The background is quite confusing. It is not clear if the robot aims primarily to patients with stroke, as the first lines suggest, or to orthopedic patients (line 53). I agree that rehabilitation robots can be used in both populations, but in the current form, the introduction is hard to follow. Moreover, a more in-depth analysis of the topic is desirable.
• The characteristics of the actuators and the sensors should be included to improve clarity.
• Some typos were noted across the text.
• I suggest a general revision of the language.

Author Response

Cover letter

Dear Reviewer:

 

Thank you for your comments and suggestions. They help us a lot to improve the quality of this paper. And responses are as follow:

 

Firstly, we are very sorry about the main points of this paper are not obvious due to the writing logic. Thus, Abstract and Introduction have been modified carefully. A new Table 1 shows the comparison of typical rehabilitation robots.

 

The originality of this robot is adduction/abduction training of hip joint, and it’s working method could avoid frequent patient handling between the wheelchair and the rehabilitation robot. Focuses of this paper are the design of a 4-DOF spatial workspace rehabilitation robot, the human joint analysis method used for guaranteeing joint safety in the working method of this robot and the trajectory tracking experiment.

 

Main

 

We are very in agreement with the point that the design of rehabilitation robots consists of the mechanical design and the control strategy design. Control strategy is indispensable to robots. But the basic control strategy is not necessary to the main points of this paper. And there are also some rehabilitation robot articles without detail description of control:

[10]. Goergen, R.; Valdiero, A. C.; Rasia, L. A.; Oberdorfer, M.; de Souza, J. P.; Goncalves, R. S., Development of a Pneumatic Exoskeleton Robot for Lower Limb Rehabilitation. IEEE ... International Conference on Rehabilitation Robotics : [proceedings] 2019, 2019 (1), 187-192.

[19]. Wang, K.-Y.; Yin, P.-C.; Yang, H.-P.; Tang, X.-Q., The man-machine motion planning of rigid-flexible hybrid lower limb rehabilitation robot. Advances in Mechanical Engineering 2018, 10 (6), 1-11.

[26]. Liao, Z.; Yao, L.; Lu, Z.; Zhang, J., Screw theory based mathematical modeling and kinematic analysis of a novel ankle rehabilitation robot with a constrained 3-PSP mechanism topology. Int J Intell Robot Appl 2018, 2 (3), 351-360.

[29]. Rakhodaei, H.; Saadat, M.; Rastegarpanah, A.; Abdullah, C. Z., Path planning of the hybrid parallel robot for ankle rehabilitation. Robotica 2014, 34 (1), 173-184.

[Plus].       Wang, H.; Feng, Y.; Yu, H.; Wang, Z.; Vladareanuv, V.; Du, Y., Mechanical design and trajectory planning of a lower limb rehabilitation robot with a variable workspace. International Journal of Advanced Robotic Systems 2018, 15 (3).

 

The semi-close loop position control is selected in the trajectory tracking experiment, and it is more suitable than other controls in this accurate trajectory training (page 14). As it is widely known, no details are shown in this paper.

 

Interaction forces could be detected by the tension/compression force sensor as shown in Figure 3. It is an important parameter which could be used for active training and other safety detections. The healthy subject relaxed his leg during the experiment, thus the interaction force information is not very meaning to the experiment result analysis. Trajectory accuracy and whether the motion of human joints is same as the calculation are the focuses of this experiment.

 

This robot actually just provided passive joint movement in the trajectory tracking experiment. But we think it is enough to verify the main points of this experiment. That is, the accuracy of the robot trajectory planning and the feasibility of the human joint analysis method. Of course this robot could provide other trainings such as active training and resistance training, and they might be introduced in another article. If you are really interested in this part, you could give a glimpse at other research papers of our team (such as reference 17 and 21).

 

We are very sorry that the solution to muscular spasticity is not finished. Our plan is stopping the training and warning to the doctor while the interaction force is abnormal. But this work is interrupted by 2019-nCoV. As for the safety of this robot, it is guaranteed by the main works shown in this paper. More specifically, patients own different range of motions of joints, an analysis method for obtaining human joint motions is proposed to guarantee patients’ joint safety in this end carrying training method (updating in Abstract and Introduction).

 

The end effector displacement is planned through the trajectory planning method mentioned in this paper. The positions of the trajectory points can be obtained directly from trajectory analytical formula (eq15 17); the velocity and acceleration between every point are planned to make speed smooth (page 14). As this part is the work of others, we cannot show more description in this paper.

 

This robot provides a new end carrying training method based on an analysis method for obtaining human joint moitons. It’s feasibility and safety could be confirmed though the experiment. More trials in patients are very hard to achieved in this period.

 

Other

 

The background is modified. ‘Arthroscopy’ is changed as ‘surgery’ to avoid misunderstanding. There are also some relative references in this paper (30,31). Circumduction training is a thigh conical motion combined with the flexion/extension and the adduction/abduction, and it is confirmed by the doctor of our team that circumduction training could be useful in some situation. Circumduction training is selected to exhibit the capability of this robot; the main reason is that the circumduction training could seldom be performed by other robots. And it could also indicate the necessary of hip adduction/abduction training.

 

The information of sensors is added in this paper (page 4 and 5).

 

 

Typos and language problems have been modified. If there are still problems, we will search English editing help to the publisher.

 

Thank you very much for your patience.

 

Sincerely yours,

Hongbo Wang and et.

 

 

Round 2

Reviewer 1 Report

Paper remain focused on the technical design of the proposed device and the authors are optimistic on a future clinical application for stroke patients

Anyway at least a small group of stroke patients should be involved as safety and feasibility study as first step for clinical application.

As it is conceived remains unclear the advantages compared to standard therapy provided by physiotherapists which seems to be more safe as stroke patients are not homogeneous and they can react very differently to the stimulation provided by the device

Reviewer 2 Report

After the revision, the Authors slightly improved the quality of the paper.
However, most of my concerns were not addressed. Therefore, I cannot recommend this paper for publication.