WeP01-08
Proceedings of the 2005 IEEE 9th International Conference on Rehabilitation Robotics June 28 - July 1, 2005, Chicago, IL, USA
Control System for Pneumatically Controlled Glove to Assist in Grasp Activities Tiffany Kline, B.S., Derek Kamper, Ph.D., Brian Schmit, Ph.D.
velocity [13]. Similarly, assisted unilateral training with a PUMA robot led to increased Fugl-Meyer Motor Assessment scores [14]. Unfortunately, there are very few robotic devices developed specifically for improving hand function. The Rutgers Hand Master II force-feedback glove is one device that has been used for rehabilitation [16]. This system is comprised of pneumatic pistons that are situated on the palmar surface of the hand. Although this system is lightweight (less than 100g), the positioning of the exoskeleton on the palm of the hand does not allow for manipulation of real objects and limits the full-range of finger movement. A second device that can be used for therapy is the CyberGrasp. This glove is expensive and weighs over 500g. Another concern with this design is that the fingers are pulled into extension, thereby raising concerns of joint hyperextension and subsequent injury. In order to address these concerns, we have developed a pneumatically actuated glove that allows training with real objects as well as with a virtual environment. The system is lightweight, with a mass of less than 100g. There is minimal calibration required to work with the sensors. Also, although the bladder is situated on the palm of the hand, the size of the bladder will not interfere with the user’s interaction with the environment. Finally, the control scheme allows possible use of muscle activity to activate assistance. This allows active involvement of the subject during training sessions which may prove to have better results in rehabilitation of hand function.
Abstract— A pneumatically controlled glove has been developed at the Rehabilitation Institute of Chicago in order to study its use on improving hand functions for individuals with hand impairment following stroke. The methods of the control system and glove design are presented in this article. Preliminary data has been collected on neurologically healthy subjects to demonstrate the training regime, and also to show the ability of the glove to assist in extending the fingers for grasping objects. Data from a stroke survivor who completed training is also shown.
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I. INTRODUCTION
TROKE is among the leading causes of adult disability in the United States [1,2,5]. Chronic impairment of the upper extremity occurs in roughly one-third of all stroke survivors [5]. While finger flexion often appears spontaneously within weeks after a cerebrovascular accident, finger extension is less likely to exhibit recovery [6]. The resulting distal limb impairment is especially problematic, since proper hand function is crucial to carrying out activities of daily living. A study from the UK reports that over half of the subjects studied are dependent on others for assistance in ADLs six months post-stroke [7]. Previous studies have shown that therapy has beneficial effects on rehabilitation following stroke. For example, changes in the cortical representations of a hand muscle have been detected in humans following intensive upper extremity therapy [8,9]. After two weeks of training, the cortical area of the brain capable of eliciting motor evoked potentials in the abductor pollicis brevis muscle in response to magnetic stimulation increased by more than 65%. This observation has triggered the development of robots and robot-therapy protocols for the rehabilitation of reaching in individuals with stroke [10,11,12]. Various robots have shown improvement in arm function following training. Therapeutic straight-line reaching assisted by the ARM Guide resulted in improved active range of motion and peak
II. PROCEDURE A. Materials The glove contains a single chamber bladder that acts as a single unit during inflation. The layout of the bladder is shown in Figure 1. This bladder is sewn onto the palmar side of a nylon/lycra glove with a dorsal zipper to ease donning of the glove. The use of nylon/lycra material for the glove allows a secure fit to subjects with different finger widths. The length of the digits allows for a variety of finger lengths such that shorter fingers will leave space at the tip of the finger. Figure 2 shows the glove with goniometers attached. Inflation of the air bladder forces straightening of the bladder channels, thereby assisting in extension of the fingers. The amount of torque applied at the joints is a factor of both the subject’s finger lengths as well as the
Manuscript received February 16, 2005. This work was supported by grant H133E020724-03 (Rehabilitation Engineering Research Center) from the National Institute on Disability and Rehabilitation Research and by the Coleman Foundation T. Kline is with the Neuromechanics Laboratory at Marquette University, Milwaukee, WI 53233 USA (phone: 312-238-2993; fax: 312238-2209, tiffany.kline@ mu.edu). D. Kamper is with the Sensory and Motor Performance Program at the Rehabilitation Institute of Chicago, Chicago, IL 60073 USA (
[email protected]). B. Schmit is with the Neuromechanics Laboratory at Marquette University, Milwaukee, WI 53233 USA (brian.schmit@ mu.edu).
0-7803-9003-2/05/$20.00 ©2005 IEEE
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of the fingertip along the stereotypical trajectory is determined by the diameter of the object. The diameter of the object is used as the height of the finger from the MCP joint in the y direction (see Fig. 4). The spiral trajectory may be expressed in Cartesian coordinates (2). With the addition of a constraint fixing DIP angle as a function of PIP angle, inverse kinematics may be used to solve the set of equations, translating fingertip location into MCP, PIP and DIP joint angles.
angle of flexion. Therefore the assistance applied by the glove is dependent on the subject. The bladder is connected through a servo valve (Pressure Control Valve, QB02005, Proportion-Air, McCordsville, Indiana) to a pressure reservoir (1104360, Jun-Air, Denmark). The servo valve allows pressures between 0-5 psi to inflate the glove. Another port on the bladder is connected to a pressure relief valve (check valve w/ 6.1 psi spring, 246301000, HalkeyRoberts, Saint Petersburg, Florida) that opens at 6.1 psi to avoid overinflation.
r = A * (exp(ș * cot(b))) A = 1.3394 * (ld + lm + lp) – 23.255 b = 1.633
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r and ș represent the position in polar coordinates where r represents the distance from the origin and ș represents the angle or rotation. ld, lm, and lp: lengths of the distal, middle and proximal phalange respectively measured on the index finger of each subject.. Units are in mm. The equations used to represent the finger end-point in terms of joint angles are:
Figure 1: Bladder layout. Width of each digit chamber is 2 cm. The length of the bladder from base to tip of middle digit is 23 cm.
x = ld * sin(ș1+ș2 +ș3) + lm * sin(ș1+ș2) + lp * sin(ș1) y = ld * cos(ș1+ș2+ș3) + lm * cos(ș1+ș2) + lp * cos(ș1) ș3 = 0.7 * ș2
Angle measurements from the proximal interphalangeal (PIP) joint of the index finger and metacarpophalangeal (MCP) joint of the middle finger are recorded using electrogoniometers (F35, Biometrics, Ladysmith, Virginia). Muscle activity is recorded using active surface electromyography (EMG) electrodes (Delsys Inc., Boston, Massachusetts). Electrodes are placed on the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) muscles of the gloved arm to sample muscle activity. Each EMG signal is passed through the DelSys amplifier, full-wave rectified, and low-pass filtered before sampling.
(2)
ș1, ș2, and ș3: MCP, PIP, and DIP joints, respectively. The locations of x and y are shown in Figure 4. The origin is at the center of the MCP joint.
B. Methods The pneumatic glove is being used in a study evaluating the efficacy of rehabilitative training of grasping in stroke survivors with chronic hand impairment. The training procedure involves three one-hour sessions per week for six weeks. At each session the subject is presented a series of 15 real objects and 15 virtual objects. The subject is asked to reach for the objects and then hold the object for several seconds. Figure 3 shows a subject during training in the virtual environment. Goggles are worn to display the image seen on the computer to the user. A tracker is placed on the hand and helmet to sense the position and orientation of the user. The glove provides assistance for finger extension as needed. Actual joint angles are compared with the desired angle necessary for obtaining sufficient opening to grasp the object. The fingertip trajectories are derived from the stereotypical spiral trajectories (1) observed in a study examining fingertip trajectories during grasp in neurologically healthy subjects [15]. The required location
Figure 2: Pictures of the dorsal and volar surfaces of the glove.
A computer controlled proportional-derivative controller regulates the pressure necessary to maintain the required angle for both the PIP and MCP joints during reaching. The control regulates pressure to the glove based on the greatest angular flexion error (i.e. if PIP angle varies by 20 degrees from desired angle while MCP angle varies by 5 degrees, pressure will be controlled based on the error of the PIP joint). When the fingers are extended further then the setpoint, pressure to the glove is reduced to maintain the necessary joint angles. EMG feedback may be incorporated to allow active participation of the user. The system senses muscle activity through the electrodes; in this case air pressure is only provided to assist extension when EDC activity exceeds a predetermined threshold (Fig. 5). Two different control strategies are employed for the grasp portion of the grasp-and-release training dependent on 79
system in monitoring EDC activity as well as providing assistance to achieve the desired MCP and PIP angles during a grasp-and-release procedure. The full rehabilitation protocol, consisting of a total of 18 training sessions, has been completed on one stroke survivor to date. In order to reduce set-up time, therapist rather than EMG control of grasp-and-release assistance was instituted. Functional ability was assessed pre- and post-training.
whether virtual or actual objects are used. When virtual objects are displayed to the user, the system monitors the point at which the hand is sufficiently extended to hold the object. When this condition is met, a signal is sent to the virtual reality (VR) program to allow grasp of the object. The object then becomes attached to the user’s hand once the hand is properly positioned in space to grasp the displayed object. When the virtual object is held, the glove control system continues to regulate pressure to maintain the desired joint angles in order to simulate holding a real object.
III. RESULTS The extension torque provided by the glove was first measured by inflating the glove against a frame connected to a torque cell (device described by Kamper et.al. [1]) for different glove flexion angles. These measurements show that the peak extension torque generated varies linearly with flexion angle. At 45 degrees of flexion the extension torque provided by the glove was .2 Nm and at a flexion of 60 degrees torque was .4 Nm. These values are in the range of the passive MCP torques seen in stroke survivors [1]. PIP (deg)
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Figure 3: Picture of the subject with the VR equipment. Picture was taken during rehabilitation training session.
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When real objects are displayed to the user, the therapist working with the subject signals that proper hand position is achieved by flipping a switch on a hand-held box. When this command of “object hold” is sent to the control system, pressure is released from the glove in order to allow the user to pick up the object.
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Figure 5: Displays a single grasp and release trial for a normal subject. Top chart displays the desired (dashed) and actual (solid) PIP angle (degrees), second chart displays desired and actual MCP angle (degrees), third chart displays the pressure (psi), fourth chart displays extensor EMG (volts), and fifth chart displays flexor EMG (volts).
Neurologically healthy subjects then performed trials according to the training paradigm to test device efficacy. They maintained a flexed posture such that the glove controlled the opening of their hand to the desired position for each object (See Fig. 5 for a representative trial). The subject was asked to maintain flexion while co-contracting, thereby triggering pneumatic assistance of extension by providing an extensor EMG signal without creating actual extension. This activity is seen in the EDC signal which is active between 7 to 26 seconds (Fig. 5). The subject then relaxed while the glove controlled pressure to maintain the desired MCP and PIP angles. The bottom chart shows flexor activity necessary to hold the object when the pressure was released. At 42 second the switch was activated to allow the subject to grasp the object. From 4060 seconds both EDC and FDS activity are present. At 60 seconds the subject actively attempted to release the object
Figure 4: Image of finger representing location of (x, y) origin.
The release portion of the grasp-and-release paradigm is accomplished by monitoring EDC activity. A threshold based on the subject’s maximum recorded EDC activity is set. When the object is held, and activity greater then this threshold is recorded from the EDC muscle, a pressure of 5 psi is used to inflate the glove in order to assist the subject in object release. If EDC muscle activity is not available or not sufficient to signal release the therapist is able to flip a switch commanding the control system to assist in object release. Data has been collected on three neurologically intact subjects to show the proper function of the control system using EMG recordings. These trials were conducted in order to demonstrate the proper operation of the control 80
A greater understanding of the ability of this pneumatic glove to aid in hand rehabilitation following stroke will become evident as more individuals of varying ability are enrolled in the study.
as seen by an increase in extensor activity. The control system senses this attempt and provides 5 psi to assist in object release and extension of the digits. Figure 6 shows the pressure and angle measurements at the PIP joint of the index finger and MCP joint of the middle finger. The pressure is released at about 6 seconds to allow the subject to grasp the object. For the stroke survivor who completed the training, a series of functional ability assessments were complete prior to the study and at the completion of the 6 weeks. Results of one of these measures showed that the time needed to carry out tasks on the Wolf Motor assessment improved for 4 of the 8 activities while the remaining 4 tests showed no change.
ACKNOWLEDGMENT "This work was supported by grant H133E020724-03 (Rehabilitation Engineering Research Center) from the National Institute on Disability and Rehabilitation Research and by the Coleman Foundation." REFERENCES [1]
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Figure 6: Plot of angles and pressure during a reaching trial for a subject with hand impairment subsequent to stroke. Dashed lines in upper two plots represent the desired angle. Solid lines in the upper two plots represent the actual measured angle. Bottom plot shows the pressure supplied by the glove during the trial.
[7] [8] [9]
IV. DISCUSSION The training paradigm (shown in Figure 5) is effective at achieving the desired joint positions in order to grasp an object. The release of the object is appropriately controlled by the extensor EMG. The pneumatic glove developed here has some positive features. With assistance, the glove can be donned and doffed fairly quickly by individuals with even severe impairment. The mass of the system on the users hand is minimal and allows active movement of the impaired arm. From the single subject that this glove has been tested on, there is evidence to suggest that some improvement of the impaired arm occurs. Due to the small concentric torque (less then 1 Nm) that can be achieved by inflation to 5 psi, a future step will involve increasing the inflation pressure with the hopes that a greater torque can be produced by the glove to assist in extension. Additionally, we will provide for individuation of assistance by creating a separate air chamber, under independent control, for each digit. This will also improve air flow.
[10] [11]
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[14] [15] [16]
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