We developed a real-time mirror robot system for functional recovery of hemiplegic arms using automatic control technology, conducted a clinical study on healthy subjects, and determined tasks through feedback from rehabilitation doctors. This simple mirror robot can be applied effectively to occupational therapy in stroke patients with a hemiplegic arm.
Mirror therapy has been performed as effective occupational therapy in a clinical setting for functional recovery of a hemiplegic arm after stroke. It is conducted by eliciting an illusion through use of a mirror as if the hemiplegic arm is moving in real-time while moving the healthy arm. It can facilitate brain neuroplasticity through activation of the sensorimotor cortex. However, conventional mirror therapy has a critical limitation in that the hemiplegic arm is not actually moving. Thus, we developed a real-time 2-axis mirror robot system as a simple add-on module for conventional mirror therapy using a closed feedback mechanism, which enables real-time movement of the hemiplegic arm. We used 3 Attitude and Heading Reference System sensors, 2 brushless DC motors for elbow and wrist joints, and exoskeletal frames. In a feasibility study on 6 healthy subjects, robotic mirror therapy was safe and feasible. We further selected tasks useful for activities of daily living training through feedback from rehabilitation doctors. A chronic stroke patient showed improvement in the Fugl-Meyer assessment scale and elbow flexor spasticity after a 2-week application of the mirror robot system. Robotic mirror therapy may enhance proprioceptive input to the sensory cortex, which is considered to be important in neuroplasticity and functional recovery of hemiplegic arms. The mirror robot system presented herein can be easily developed and utilized effectively to advance occupational therapy.
For patients with stroke, dysfunction of a hemiplegic arm has debilitating effect. The ability to perform bimanual activities is essential for daily life, but functional deficit of a hemiplegic arm often remains even a few years after stroke onset. Among various training programs in the hospital, an exercise to increase the range of motion or passive repetition of simple tasks have little effect on functional recovery of a hemiplegic arm. For this reason, training of meaningful tasks related to activities of daily living (ADLs) has been applied to occupational therapy in hospitals.
The effects of mirror therapy were proven by previous studies in neurorehabilitation1-4. Mirror therapy is conducted by eliciting an illusion through use of a mirror as if the hemiplegic arm is moving in real-time while moving the healthy arm. It can facilitate brain neuroplasticity by activation of the sensorimotor cortex1. Thus, motor power and function of the hemiplegic arm can be improved. However, conventional mirror therapy has a critical limitation in that the hemiplegic arm is not actually moving.
Therefore, we developed a real-time 2-axis mirror robot system as a simple add-on module to conventional mirror therapy, using closed feedback mechanism. This may convey proprioceptive input to the sensory cortex, which is considered important in neuroplasticity and functional recovery of a hemiplegic arm (Figures 1 and 2)5-7.
All of the procedures were reviewed and approved by the Institutional Review Board of Seoul National University Hospital.
1. Mirror Therapy Tasks
2. Components of the Mirror Robot System
3. Design of Mirror Robot System
4. Clinical Application of the Mirror Robot System
Six healthy subjects conducted a 'pen marking task' (touching the two small boards alternately with a pen attached on the healthy hand as shown in Figure 17) 10 times which took on average 106 sec per subject. No adverse event was observed, and robotic mirror therapy was proven to be feasible.
In addition, a clinical study on rehabilitation doctors was conducted. We requested expert opinions to determine appropriate tasks for effective robotic mirror occupational therapy. With feedback from 6 rehabilitation doctors, the degree of illusion elicited by the mirror robot was highest for "ball in holes" and "moving a cup" tasks (7.2 out of 10 on a numerical rating scale [NRS] for each), followed by "soccer game" (7.0/10) and "dots tracing" tasks (6.5/10). Regarding the synchronicity of movement between both arms during robotic mirror therapy, "moving a cup" task had an NRS score of 7.0/10, followed by "soccer game" and "dots tracing" (6.8/10 each), and "ball in holes" (6.2/10) (Figure 3). Among these 4 tasks, rehabilitation doctors recommended "soccer game" as a useful task for ADL training in patients with stroke.
We conducted a clinical trial for stroke patients with mirror robot for 30 min per day for 2 weeks (10 sessions). Subjects need to meet the following inclusion criteria: 1) over 18 years old; 2) supratentorial stroke diagnosed between 4 months and 6 years ago; and 3) upper-limb hemiplegia with Medical Research Council (MRC) grade 2 or less. Main exclusion criteria are as follows: 1) modified Ashworth scale of grade 3 or more (severe spasticity); 2) mini-mental state examination score less than 12; and 3) global or sensory aphasia.
A 60-year-old male stroke patient with right basal ganglia hemorrhage and left hemiplegia 19 months prior received robotic mirror therapy for 2 weeks. Robotic mirror therapy consisted of 4 tasks ("ball in holes", "moving a cup", "soccer game", and "dots tracing"). After the patient accomplishes the 10th visit, he conducted follow-up functional evaluations. The Fugl-Meyer assessment scale of the hemiplegic arm improved from 12 to 17 out of 66, and modified Ashworth scale of elbow flexors (for spasticity) was reduced from grade 2 to 1+. Left lateral pinch power was increased from 0 to 3 lb. Other parameters revealed no difference before and after robotic mirror therapy (Figure 18 and Table 1).
Figure 1. Conceptual Flow for the Robotic Mirror Therapy to Facilitate Proprioceptive Input. The experiment is designed in accordance with the conceptual flow for the robotic mirror therapy.
Figure 2. A Diagram of the Mirror Robot System. Movements of the healthy arm are projected to the exoskeleton attached to the hemiplegic arm by a software algorithm through input from 3 AHRS sensors. Please click here to view a larger version of this figure.
Figure 3. Various Tasks using the Mirror Robot System. The users can be trained by 2-dimensional tasks; ball in holes, soccer game, dots tracing, and moving a cup. Please click here to view a larger version of this figure.
Figure 4. Elbow Motor Assembly. Assembly steps for elbow joint motor, couplings, and elbow coupling hollow cylinder cover.
Figure 5. Bearing & Elbow Rooftop Frame Assembly. Assembly between bearing and the elbow rooftop frame assembly.
Figure 6. Elbow Support Assembly. Assembly steps for elbow motor force dispersion shaft, upper elbow support, and lower elbow support.
Figure 7. Elbow Support & Elbow Motor Assembly. Assembly steps for the elbow support and the elbow motor.
Figure 8. Wrist Motor Assembly. Assembly steps for wrist joint motor, couplings, and lower wrist coupling hollow cylinder cover.
Figure 9. Friction Reduction Ring Attachment. Attachment of the friction reduction ring to the wrist rooftop frame.
Figure 10. Handle Assembly. Assembly steps for the 3D printed handle, coupling, and the wrist motor force dispersion shaft.
Figure 11. Handle & Wrist Motor Assembly. Assembly steps for the wrist motor and the handle.
Figure 12. Joint Movement Limiter Assembly. Assembly steps for the (A) joint movement limiter, (B) length adjustment shaft, and the assembled handle.
Figure 13. Final Assembly. Assembly steps for the (A) assembled elbow motor part with the assembled wrist motor part using shaft collars and shaft, (B) assembled robot with the support walls, and (C) assembled robot with the task table. Please click here to view a larger version of this figure.
Figure 14. Block Scheme of the Automatic Control Mathematical Model. The exoskeleton robot utilizes closed feedback mechanism for real-time control.
Figure 15. Overall Software Program. The software program uses a closed feedback mechanism to drive the robot system. Please click here to view a larger version of this figure.
Figure 16. GUI of the Program. User can control and configure the program for therapy via GUI. Please click here to view a larger version of this figure.
Figure 17. A Pen Marking Task in 6 Healthy Subjects using Prototype of Mirror Robot System. Conducting a pen marking task 10 times consecutively took on average 106 sec per subject.
Figure 18. Functional Evaluation of a 60-year-old Male Patient with Chronic Right Basal Ganglia Hemorrhage. Main subsets of data that showed improvement after 10 sessions of robotic mirror therapy. Please click here to view a larger version of this figure.
Before | After 10 sessions | |
Mini-mental state examination | 29 | – |
Fugl-Meyer assessment scale (Upper extremity) |
12 | 17 |
Shoulder/elbow | 11 | 15 |
Wrist | 0 | 1 |
Hand | 1 | 1 |
Modified Ashworth scale | ||
Elbow flexor | 2 | 1+ |
Wrist flexor | 0 | 0 |
Modified Barthel index (Upper extremity) |
25 | 25 |
Jebsen hand function test | Uncheckable | Uncheckable |
Left hand power (lb) | ||
Grip | 8 | 8 |
Lateral pinch | 0 | 3 |
Palmar pinch | 0 | 0 |
Hemineglect test | ||
Line bisection test | 6/6 each | 6/6 each |
Albert test | 12/12 each | 12/12 each |
Motor evoked potential | No response | No response |
Table 1. Functional Evaluation of a 60-year-old Male Patient with Chronic right Basal Ganglia Hemorrhage.
The primary purpose of this study was to develop a real-time mirror robot system for functional recovery of a hemiplegic arm using an automatic control algorithm. The effect of robot-assisted therapy on long-term recovery of upper-limb impairment after stroke was proven beneficial in previous studies12, and various kinds of arm robots have been introduced13-20. However, previous studies of upper extremity robots that realized bilateral arm movement applied mechanical connections without using a mirror, which is different from the concept of mirror therapy14-15. Thus, our study can be an extension of their work by using an actual mirror to facilitate proprioceptive input.
To upgrade the previous system, we enabled the hemiplegic arm to move in real-time by applying AHRS sensors on the healthy arm and attaching motors to the hemiplegic elbow and wrist. Proprioceptive input from the hemiplegic arm to the sensory cortex of brain can be enhanced through the mirror robot system. Facilitation of proprioception needs to be confirmed by functional brain MRI in a future study.
It is critical for the system to have minimum synchronization delay since the mirror effect will be maximized when the delay is minimized. To achieve this, we retrieved data from sensors with minimum necessary byte count while reading them in parallel within a loop inside the software architecture. As a result, the synchronization delay between the healthy arm and the robot is only about 0.04 – 0.40 sec.
There are several limitations in this study. First, we could not include fine finger movements such as grip or pinch, and 3-dimensional tasks of conventional mirror therapy. Second, we did not fix the elbow joint of the healthy arm to preserve physiologic movement as much as possible. However, restriction of the range of elbow motion would be helpful to enhance synchronicity with the opposite elbow which is moved by the motor. Modifying the system by installing additional structure that secures the healthy side elbow will improve the synchronicity and, therefore, will increase the effect of the therapy. Third, patients who had severe spasticity or stiffness could not be included because of insufficient motor power, although the joint moved slowly. The system could be modified by replacing the motor with higher torque output to overcome moderate stiffness. However, even with strong motor, treatment to patients with severe levels of spasticity or stiffness should be avoided to prevent tendon or bone injuries due to excessive force application to the joints.
We believe, however, that the mirror robot system presented herein can be easily developed and utilized effectively to advance occupational therapy.
The authors have nothing to disclose.
This work was supported by the Brain Fusion Program of Seoul National University (800-20120444) and the Interdisciplinary Research Initiatives Program from College of Engineering and College of Medicine, Seoul National University (800-20150090).
LabVIEW | National Instruments | System design software | |
24V power supply | XP Power | MHP1000PS24 24V | Any 24V power supply should do |
AHRS sensor receiver | E2box | EBRF24GRCV | |
AHRS sensors | E2box | EBIMU-9DOFV2 | You will need total 3 sensors. Any AHRS sensors will do |
EC90 flat motor module | Maxon | 323772 + 223094 + 453231 | Any geared motor with higher than 30Nm should do. (For our custom machined parts, you will need these particular flat motor and gear module, but the gear ratio and encoder may vary) |
EC45 flat motor module | Maxon | 397172 | Any geared motor with higher than 10Nm should do (For our custom machined parts, you should use the same gear module but the gear ratio, motor, and encoder may vary) |
EPOS2 70/10 controller | Maxon | 375711 | This can be replaced with EPOS 24/5 controller |
EPOS2 24/5 controller | Maxon | 367676 | |
Connector and cable set | Maxon | 381405 + 384915 + 275934 + 354045 | You can also make these cables. Connectors and corresponding wire info can be found in "300583-Hardware-Reference-En.pdf" and "300583-Cable-Starting-Set-En.pdf" |
Coupling- Oldham, Set Screw Type | Misumi | MCORK30-10-12 | Type may vary |
Coupling- High Rigidity, Oldham, Set Screw Type |
Misumi | MCOGRK34-12-12 | Type may vary |
Shaft Collars | Misumi | SCWDM10-B | You will need 4 sets |
Shaft Collars | Misumi | SDBJ10-8 | You will need 2 sets |
Precision Linear Shaft | Misumi | PSSFG10-200 | Any straight 10mm diameter shaft with at least 200mm length should do |
Bearings with housings | Misumi | BGRAB6801ZZ | |
Elbow motor force dispersion shaft | custom machined | 3D CAD | |
Lower elbow support | custom machined | Part Drawings | |
Elbow rooftop frame | custom machined | Part Drawings | |
Support wall | custom machined | Part Drawings | You will need 2 frames. |
Elbow coupling hollow cylinder cover | custom machined | Part Drawings | |
Wrist motor force dispersion shaft | custom machined | Part Drawings | |
Wrist rooftop frame | custom machined | Part Drawings | |
Upper wrist coupling hollow cylinder cover | custom machined | Part Drawings | |
Lower wrist coupling hollow cylinder cover | custom machined | Part Drawings | |
Joint movement limiter | custom machined | Part Drawings | |
Handle | 3D printed | Part Drawings | |
Upper elbow support | 3D printed | Part Drawings | |
Friction reduction ring | 3D printed | Part Drawings | |
Acrylic mirror | custom laser cutting | Part Drawings | |
Task table | custom machined | Part Drawings | |
Silicone sponge | |||
DOF limiter | 3D printed | Part Drawings | |
DOF limiter lid | 3D printed | Part Drawings | |
Healthyarm handle | 3D printed | Part Drawings | |
Ball rollers – Press fit | Misumi | BCHA18 | |
Goalpost | 3D printed | Part Drawings | |
Circle trace | 3D printed | Part Drawings | |
Angled assist | 3D printed | Part Drawings | Optional |
Curved assist | 3D printed | Part Drawings | Optional |
Plain assist | 3D printed | Part Drawings | Optional |
Task board | custom laser cutting | Part Drawings |