Rehabilitation robotics: pilot trial of a spatial extension for MIT-Manus.

Abstract

BACKGROUND: Previous results with the planar robot MIT-MANUS demonstrated positive benefits in trials with over 250 stroke patients. Consistent with motor learning, the positive effects did not generalize to other muscle groups or limb segments. Therefore we are designing a new class of robots to exercise other muscle groups or limb segments. This paper presents basic engineering aspects of a novel robotic module that extends our approach to anti-gravity movements out of the horizontal plane and a pilot study with 10 outpatients. Patients were trained during the initial six-weeks with the planar module (i.e., performance-based training limited to horizontal movements with gravity compensation). This training was followed by six-weeks of robotic therapy that focused on performing vertical arm movements against gravity. The 12-week protocol includes three one-hour robot therapy sessions per week (total 36 robot treatment sessions). RESULTS: Pilot study demonstrated that the protocol was safe and well tolerated with no patient presenting any adverse effect. Consistent with our past experience with persons with chronic strokes, there was a statistically significant reduction in tone measurement from admission to discharge of performance-based planar robot therapy and we have not observed increases in muscle tone or spasticity during the anti-gravity training protocol. Pilot results showed also a reduction in shoulder-elbow impairment following planar horizontal training. Furthermore, it suggested an additional reduction in shoulder-elbow impairment following the anti-gravity training. CONCLUSION: Our clinical experiments have focused on a fundamental question of whether task specific robotic training influences brain recovery. To date several studies demonstrate that in mature and damaged nervous systems, nurture indeed has an effect on nature. The improved recovery is most pronounced in the trained limb segments. We have now embarked on experiments that test whether we can continue to influence recovery, long after the acute insult, with a novel class of spatial robotic devices. This pilot results support the pursuit of further clinical trials to test efficacy and the pursuit of optimal therapy following brain injury.

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BioMed Central
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(page number not for citation purposes)
Journal of NeuroEngineering and
Rehabilitation
Open Access
Research
Rehabilitation robotics: pilot trial of a spatial extension for
MIT-Manus
Hermano I Krebs*1,2, Mark Ferraro3, Stephen P Buerger1,
Miranda J Newbery1,4, Antonio Makiyama5, Michael Sandmann5,
Daniel Lynch3, Bruce T Volpe2,3 and Neville Hogan1,6
Address: 1Massachusetts Institute of Technology, Mechanical Engineering Department, Cambridge, MA, USA, 2Weill Medical College of Cornell
University, Department Neurology and Neuroscience, New York, NY, USA, 3Burke Medical Research Institute, White Plains, NY, USA, 4Imperial
College, London, UK, 5Interactive Motion Technologies, Inc., Cambridge, MA, USA and 6Massachusetts Institute of Technology, Brain and
Cognitive Sciences, Cambridge, MA, USA
Email: Hermano I Krebs* - hikrebs@mit.edu; Mark Ferraro - mferraro@burke.org; Stephen P Buerger - steveb@mit.edu;
Miranda J Newbery - miranda.newbery@rca.ac.uk; Antonio Makiyama - makiyama@interactive-motion.com;
Michael Sandmann - mike@interactive-motion.com; Daniel Lynch - dlynch@burke.org; Bruce T Volpe - bvolpe@burke.org;
Neville Hogan - neville@mit.edu
* Corresponding author
Abstract
Background: Previous results with the planar robot MIT-MANUS demonstrated positive benefits in trials with
over 250 stroke patients. Consistent with motor learning, the positive effects did not generalize to other muscle
groups or limb segments. Therefore we are designing a new class of robots to exercise other muscle groups or
limb segments. This paper presents basic engineering aspects of a novel robotic module that extends our
approach to anti-gravity movements out of the horizontal plane and a pilot study with 10 outpatients. Patients
were trained during the initial six-weeks with the planar module (i.e., performance-based training limited to
horizontal movements with gravity compensation). This training was followed by six-weeks of robotic therapy
that focused on performing vertical arm movements against gravity. The 12-week protocol includes three one-
hour robot therapy sessions per week (total 36 robot treatment sessions).
Results: Pilot study demonstrated that the protocol was safe and well tolerated with no patient presenting any
adverse effect. Consistent with our past experience with persons with chronic strokes, there was a statistically
significant reduction in tone measurement from admission to discharge of performance-based planar robot
therapy and we have not observed increases in muscle tone or spasticity during the anti-gravity training protocol.
Pilot results showed also a reduction in shoulder-elbow impairment following planar horizontal training.
Furthermore, it suggested an additional reduction in shoulder-elbow impairment following the anti-gravity
training.
Conclusion: Our clinical experiments have focused on a fundamental question of whether task specific robotic
training influences brain recovery. To date several studies demonstrate that in mature and damaged nervous
systems, nurture indeed has an effect on nature. The improved recovery is most pronounced in the trained limb
segments. We have now embarked on experiments that test whether we can continue to influence recovery, long
after the acute insult, with a novel class of spatial robotic devices. This pilot results support the pursuit of further
clinical trials to test efficacy and the pursuit of optimal therapy following brain injury.
Published: 26 October 2004
Journal of NeuroEngineering and Rehabilitation 2004, 1:5doi:10.1186/1743-0003-1-5
Received: 30 August 2004
Accepted: 26 October 2004
This article is available from: http://www.jneuroengrehab.com/content/1/1/5
© 2004 Krebs et al; licensee BioMed Central Ltd.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Background
Rather than using robotics as an assistive technology for a
disabled individual, our research focus is on the develop-
ment and application of robotics as a therapy aid, and in
particular a tool for therapists. We foresee robots and
computers as supporting and enhancing the productivity
of clinicians in their efforts to facilitate a disabled individ-
ual's functional motor recovery. To that end, we deployed
our first robot, MIT-MANUS (see figure 1), at the Burke
Rehabilitation Hospital, White Plains, NY in 1994 [1]. In
the last ten years, MIT-MANUS class robots have been in
daily operation delivering therapy to over 250 stroke
patients. Hospitals presently operating one or more MIT-
MANUS class robots include Burke (NY), Spaulding
(MA), Rhode Island (RI), Osaka Prefectural (Japan) and
Helen Hayes (NY) Rehabilitation Hospitals, and the Bal-
timore (MD) and Cleveland (OH) Veterans Administra-
tion Medical Centers.
Most of the work to date has focused on the fundamental
question of whether task specific training affects motor
outcome and positively influences brain recovery. These
efforts directly confront the overwhelming task of revers-
ing the effects of natural injury where lesion size, type and
location profoundly determine outcome, and applying
controlled conditions in environment and training – nur-
ture – to exploit the ability of the mature nervous system
to learn, adapt and change.
Stroke Inpatient during Therapy at the Burke Rehabilitation Hospital (White Plains, NY)
Figure 1
Stroke Inpatient during Therapy at the Burke Rehabilitation Hospital (White Plains, NY). Therapy is being conducted with a
commercial version of MIT-MANUS (Interactive Motion Technologies, Inc., Cambridge, MA).

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Through our work with MIT-MANUS, providing task spe-
cific training for patients' with moderate to severe hemi-
paresis, we have gathered
(summarized below) that nurture has a significant impact
in speeding motor recovery of the paretic shoulder and
elbow, and that robot therapy is effective in delivering the
necessary exercise. This recovery is most pronounced in
the trained muscle groups and limb segments. Encour-
aged by these positive results, we have expanded our
project to develop a family of novel, modular robots,
designed to be used independently or together to rehabil-
itate other muscle groups and limb segments. This paper
describes two different implementations of a new module
developed at MIT that expands the capabilities of MIT-
convincing evidence
MANUS to include motion in a three-dimensional work-
space. We will present both implementations, the basic
engineering differences between these modules, and pilot
clinical results from their use with stroke patients.
Proof-of-Concept
Volpe [2] reported the composite results of robotic train-
ing with 96 consecutive stroke inpatients admitted to
Burke who met inclusion criteria and consented to partic-
ipate [3-7,2]. Patients were randomly assigned to either an
experimental or control group and although the patient
groups were comparable on all initial clinical evaluation
measures, the robot-trained group demonstrated signifi-
cantly greater motor improvement (higher mean interval
Table 1: Mean interval change in impairment and disability (significance p < 0.05).
Between Group Comparisons: Final Evaluation Minus Initial Evaluation Robot Trained (N = 55) Control (N = 41)P-Value
Impairment Measures (±sem)
Motor Power (MP)
Motor Status shoulder/elbow (MS-se)
Motor Status Wrist/Hand (MS/wh)
4.1 ± 0.4
8.6 ± 0.8
4.1 ± 1.1
2.2 ± 0.3
3.8 ± 0.5
2.6 ± 0.8
<0.01
<0.01
NS
Table 2: Data on the Ten (10) Community Dwelling Stroke Volunteers
AgeHandedLesion foci Lesion sideMonths strokeFugl-Meyer adm (/66)
59
53
44
63
82
72
41
72
57
77
Left
Ambi
Right
Right
Right
Right
Right
Right
Right
Right
AVM hem.
Intracerebral bleed
Carotid dissection
Cerebral embolism, subcortical
Cerebral embolism, subcortical
Carotid endarectomy
cortical/subcortical and basal ganglia stroke
cortical/subcortical stroke
Cerebral embolism, subcortical
cerebral embolism, mixed
Left
Left
Left
Left
Left
Right
Right
Right
Right
Right
16.5
88.5
36
58
69
24
96
47.5
48
16
11
18
11
9
9
24
17
9
30
34
Table 3: Anti-Gravity Vertical Module Pilot Study. Results from nine (9) outpatients that continued for an additional 6 weeks of training
in the vertical module robotic unit. Statistical tests showed that outcomes at discharge from planar robot protocol were distinct from
admission (B vs. A), and there was a trend favoring further improvement when comparing discharge from anti-gravity protocol with
discharge from the planar protocol (C vs. B). Our protocol was safe and did not increase tone.
Timeline N = 9A – AdmissionB – Discharge from planar robot protocolC – Discharge from anti-gravity protocol
F-M s/e (/42)
MSS s/e (/40)
MP
Ashworth
12.7 ± 1.6
18.1 ± 1.9
26.5 ± 3.5
8.0 ± 1.4
14.8 ± 2.0 (p = 0.03, S)
19.9 ± 2.0 (p = 0.01, S)
33.3 ± 3.6 (p < 0.01, S)
4.9 ± 0.99 (p < 0.03, S)
17.0 ± 1.9 (p = 0.19, NS)
21.5 ± 1.8 (p = 0.29, NS)
38.8 ± 2.4 (p = 0.07, NS)
4.4 ± 1.01 (p = 0.67, NS)

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change ± standard error measurement) than the control
group on the Motor Status and Motor Power scores for
shoulder and elbow (see Table 1). In fact, the robot-
trained group improved twice as much as the control
group in these measures. These gains were specific to
motions of the shoulder and elbow, the focus of the robot
training. There were no significant between-group differ-
ences in the mean change scores for wrist and hand func-
tion. Similar results were gathered in patients who have
had a paralyzed upper extremity after stroke for at least
one year [8-10] (See Table 1).
Description of Robots
Modularity and Integration Potential
MIT's experience with well over 250 stroke patients has
reinforced the importance of one of our core design spec-
ifications: Modularity. From the outset we believed that
modularity is essential to success in robotic therapy, par-
ticularly in extending the approach to patients suffering
from distinct afflictions. Consider, for example, patients
undergoing surgery at the wrist (e.g., Colles Fracture) who
might not require a device that manipulates the payload
of all the degrees-of-freedom (DOF) of the arm. Therapy
for these patients requires only the wrist robot [11-13].
Conversely there will be patients for whom different mod-
ules must be coupled to deliver therapy and carry the pay-
load of the human arm. Presently MIT has deployed four
modules into the clinic (Burke Rehabilitation): a planar 2-
dof active module; vertical 1-dof active module; wrist 3-
dof active module; and 1-dof passive grasp module.
Features common to all modules
All of our robot modules are specifically designed and
built for clinical rehabilitation applications. Unlike most
industrial robots, they are configured for safe, stable, and
compliant operation in close physical contact with
humans. This is achieved using backdrivable hardware
and impedance control, a key feature of the robot control
system. Each active module can move, guide or perturb
movements of a patient's limb and can record motions
and mechanical quantities such as the position, velocity,
and forces applied.
The most profound engineering challenge specific to this
family of robots is achieving the dual goals of high force
production capability and backdrivability. Each module
must be capable of generating sufficient force to move a
patient's limb, but it must also itself be easily movable by
an elderly or frail patient. Backdrivability is essential in
keeping the patient engaged in the task and in allowing
him to observe his successful and unsuccessful attempts at
motion. Backdrivable hardware also improves the per-
formance of systems controlled by impedance controllers.
Achieving backdrivability and high force production,
together in a single machine, is often difficult and
becomes more so when the robot geometry is more
complex.
The robot control system is an impedance controller that
modulates the way the robot reacts to mechanical pertur-
bation from a patient or clinician and ensures a gentle
compliant behavior. Impedance control refers to using a
control system (actuators, sensors and computer) to
impose a desired behavior at a specified port of interac-
tion with a robot, in this case the attachment of the robot
to the patient's hand. Conceived in the early 1980's by
one of the co-authors [14], it has been applied successfully
in numerous robot applications that involve human-
motor interaction. Impedance control has been exten-
sively adopted by other robotics researchers concerned
with human-machine interaction. In rehabilitation robot-
ics impedance control has been successfully implemented
in MIT-MANUS since its clinical debut in 1994. For robots
interacting with the human, the most important feature of
the controller is that its stability is extremely robust to the
uncertainties due to physical contact [14,15]. The stability
of most robot controllers is vulnerable when contacting
objects with unknown dynamics. In contrast, dynamic
interaction with highly variable and poorly characterized
objects (to wit, neurologically impaired patients) will not
de-stabilize the impedance controller above; even inad-
vertent contact with points other than the robot end-effec-
tor will not de-stabilize the controller. This is essential for
safe operation in a clinical context.
Table 4: Anti-Gravity Vertical Module Pilot Study. Results from one naive (1) outpatient that trained for 6 weeks in the vertical module
robotic unit (no prior robot exposure).
Timeline N = 1 B – Admission to anti-gravity protocolC – Discharge from anti-gravity protocol
F-M s/e (/42)
MSS s/e (/40)
MP
Ashworth
24.0
21.8
35.0
4
27.0
31.0
43.0
1

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Planar 2-dof robot MIT-MANUS
The MIT-MANUS project was initiated in 1989 with sup-
port from the National Science Foundation. MIT-MANUS
has been in daily operation since 1994 delivering therapy
to stroke patients at the Burke Rehabilitation Hospital.
This robot has been extensively described in the literature
[4] (See Figure 1). MIT-MANUS is a planar module which
provides two translational degrees-of-freedom for elbow
and forearm motion. The 2-dof module is portable (390
N) and consists of a direct-drive five bar-linkage SCARA
(Selective Compliance Assembly Robot Arm). This config-
uration was selected because of its unique characteristics
of low impedance on the horizontal plane and almost
infinite impedance on the vertical axis. These allow a
direct-drive backdrivable robot to easily carry the weight
of the patient's arm. The mechanism is driven by brush-
less motors rated to 9.65 Nm of continuous stall torque
with 16-bit virtual absolute encoders for position and
velocity measurements (higher torques can be produced
for limited periods of time). Redundant velocity sensing
may be provided by DC-tachometers with a sensitivity of
1.8 V/rad/sec. A six degrees-of-freedom force sensor is
mounted on the robot end-effector. The robot control
architecture is implemented in a standard personal com-
puter with 16-bit A/D and D/A I/O cards, as well as a DIO
card with 32 digital lines. Besides its primary control func-
tion, this computer displays the task to both the operator
and the subject or patient via dedicated monitors. Cus-
tom-made hand holders connect a patient's upper limb to
the robot end-effector.
The selected design created a highly backdrivable robot
capable of delivering therapy in a workspace of 15" by 18"
with an end-point anisotropy of 2:1 ratio (2/3 < I < 4/3 Kg;
56.7 < static friction < 113.4 grams) and achievable
impedances between 0 and 8 N/mm. Note that the static
friction is significantly below the just noticeable differ-
ence (JNF) for force, which is 7% of the reference force.
The robot maximum achievable impedance is above the
human perception of 4.2 N/mm for a "virtual wall." The
robot is capable of delivering forces up to 45 N although
the robot target design aimed at a force of 28 N, which
corresponds to the arm strength during elbow extension
for a weak woman in seated position [16].
Vertical 1-dof Novel Robot
Following the successful clinical trials of MIT-MANUS, a
1-dof module to provide vertical motion and force was
conceived and built. The primary goal of this module is to
bring the benefits of planar therapy on MIT-MANUS to
spatial arm movements, including movement against
gravity. The module can be used independently or
mounted to MIT-MANUS for movement in a limited spa-
tial workspace. The module can permit free motion of the
patient's arm, or can provide partial or full assistance or
resistance as the patient moves against gravity. Because the
vertical module moves with the endpoint of the planar
module when the two are integrated, overall module mass
is an important design concern in addition to on-axis
mass and friction. Two embodiments are described
below.
Screw-driven module
One prototype of the 1-dof module was completed at MIT
late 2000 and is shown alongside a test stand in Figure 2.
A second clone was completed at MIT and deployed in the
clinic (Burke Rehabilitation Hospital), where it is pres-
ently collecting pilot data with stroke patients. The mod-
ule incorporates a custom-made "rollnut" and a custom-
made screw with a linear guide system. Significant effort
was engaged in the design of the screw transmission,
which provides an efficient conversion of rotary to linear
motion designed to eliminate nearly all-sliding friction in
favor of rolling contact. Its low friction provides an intrin-
sically back-drivable design. The bracket mounted to the
rollnut allows the attachment of different interfaces.
Incorporated into the design are therapists' suggestions
that functional reaching movements often occur in a
range of motion close to shoulder scaption. Thus, the
robotic therapy games that use the spatial robot focus on
movements within the 45° to 65° range of shoulder
abduction and from 30° to 90° of shoulder elevation or
flexion. A Gripmate http://www.gripmate.com is used to
hold the patient's hand in place.
This prototype has been fully characterized at MIT [17,18]
(Figures 4 and 5). In comparison to MIT-MANUS, the ver-
tical module has a greater effective endpoint mass and
friction, though the resulting system is still back-drivable.
In order to partially compensate for this increased imped-
ance, force-feedback is incorporated into the impedance
controller, resulting in a substantial reduction in friction,
down to approximately 3 N, and mass, to approximately
1 kg. This improvement is illustrated in Figure 3. The
module is capable of providing well over the force specifi-
cation of 65 N in the upward direction (20 N estimate of
patient's arm weigh) and 45 N in the downward direction,
and can achieve stiffness in excess of 10 N/mm, far greater
than the values generally used for therapy.
Linear direct-drive module
The screw-driven prototype has proven very successful
both in standalone operation and mounted at the end of
the planar module enabling spatial movement therapy in
the clinic with compliant and stable behavior. However
recent changes in linear motor technology have created
the potential to achieve similar outcomes with effective
vertical endpoint inertia comparable to the planar MIT-
MANUS and much lower friction, without the need for