U.S. patent application number 12/475821 was filed with the patent office on 2010-02-18 for variable resistance hand rehabilitation device with linear smart fluid damper and dynometer capabilities.
This patent application is currently assigned to NORTHEASTERN UNIVERSITY. Invention is credited to Don Consolini, George Galanis, Azadeh Khanicheh, Constantinos Mavroidis, James Shannon, Brian Weinberg.
Application Number | 20100041529 12/475821 |
Document ID | / |
Family ID | 41681668 |
Filed Date | 2010-02-18 |
United States Patent
Application |
20100041529 |
Kind Code |
A1 |
Weinberg; Brian ; et
al. |
February 18, 2010 |
VARIABLE RESISTANCE HAND REHABILITATION DEVICE WITH LINEAR SMART
FLUID DAMPER AND DYNOMETER CAPABILITIES
Abstract
A variable resistance hand rehabilitation device and
corresponding system. Improvements over the prior art include: a
new damping system or damper design, to reduce friction and
increase maximum force output; a dynometer feature that enables
converting the dynamic device to a static grip force measuring
device; a closed-loop controller; and a new graphic user interface
for the medical practitioner and new virtual reality game software
that allow accurate and smooth operation of the device and
increased patient motivation.
Inventors: |
Weinberg; Brian; (Brookline,
MA) ; Khanicheh; Azadeh; (Cambridge, MA) ;
Mavroidis; Constantinos; (Arlington, MA) ; Shannon;
James; (Wilbraham, MA) ; Consolini; Don;
(Southwick, MA) ; Galanis; George; (Southampton,
MA) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
NORTHEASTERN UNIVERSITY
Boston
MA
WGI D/B/A WESTFIELD GAGE CO. OVERHAUL AND REPAIR
Southwick
MA
|
Family ID: |
41681668 |
Appl. No.: |
12/475821 |
Filed: |
June 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61130484 |
May 30, 2008 |
|
|
|
Current U.S.
Class: |
482/135 |
Current CPC
Class: |
A61H 1/0285
20130101 |
Class at
Publication: |
482/135 |
International
Class: |
A63B 21/00 20060101
A63B021/00 |
Claims
1. A variable resistance hand rehabilitation device adapted to
provide a controllable velocity or a controllable resistive force
during exercises of a mammalian extremity, the device comprising: a
support structure for providing strength and structure to the
device; a handle portion moveable in a single degree of freedom and
by which the extremity performs the exercises; a controllable
damping system that is structured and arranged to provide a
selectively controlled resistance to the extremity using an
electro-rheological fluid having a resistivity that is continuously
variable throughout a stroke cycle; and at least one sensing
device, each of which is mechanically coupled to the handle portion
and each of which is adapted to provide measurement data for
controlling the resistivity of the electro-rheological fluid.
2. The device as recited in claim 1, wherein the handle portion
includes a first, movable handle portion and a second, fixed handle
portion, the first, movable hand portion having a single degree of
freedom of movement in the direction of the fixed handle
portion.
3. The device as recited in claim 2, wherein the at least one
sensing devices includes at least one of: a linear potentiometer
that is mechanically coupled to the movable handle portion and
adapted to measure linear displacement of the handle portion during
a stroke cycle; and a linear force sensing device that is
mechanically coupled to said movable handle portion and adapted to
measure a force or pressure applied by a mammalian extremity
throughout the stroke cycle.
4. The device as recited in claim 1 further comprising at least one
of: a locking mechanism that is adapted to lock the shaft in a
fixed position so that the device provides static rather than
dynamic data; and a handle return force control system that is
adapted to return the handle portion to a starting point of the
stroke elastically.
5. The device as recited in claim 4, wherein the handle return
force control system is structured and arranged to return the
handle portion to a start position of the stroke after completion
of the stroke cycle, the handle return system comprising: a pair of
notched scales having a plurality of positioning notches, each of
the pair being disposed at a distal end of the support structure; a
pair of slidable mounts, each of the pair being slidably disposed
on one of the pair of notched scales and being structured and
arranged to be fixedly attachable at a desired, discrete
positioning notch on the corresponding notched scale; and a pair of
elongate members, each of the pair being fixedly attached to one of
the pair of slidable mounts at a first end and to one of the at
least one sensing device at a second end.
6. The device as recited in claim 1, wherein the controllable
damping system includes: at least one electrode that is structured
and arranged as coaxial, concentric cylinder, a gap for the
transmission of the electro-rheological fluid being formed between
adjacent electrodes or between a single electrode and another
surface in the damping system; and a protective damper case, the
case including: a center damper case having an inner bore that is
adapted to provide a tight interference fit with an outermost
electrode of said at least one electrode; a case manifold that is
releasably attachable to one end of the center damper case; and a
case end cover that is releasably attachable to another, opposite
end of the center damper case.
7. The device as recited in claim 6, wherein the center damper case
is precision manufactured of polyoxymethylene.
8. The device as recited in claim 6, wherein the case manifold
includes at least one of: at least one electrode alignment tab,
each of said alignment tab having a thickness that is equal to the
gap distance; and a plurality of electrode alignment pin holes that
are structured and arranged to be in registration with a
corresponding plurality of alignment pin holes that are disposed on
each end of each of the plurality of electrodes; and a gland that
is adapted for holding a sealing device.
9. The device as recited in claim 8, the sealing device being
selected from a group comprising: an o-ring and a spring seal.
10. The device as recited in claim 6, wherein the case end cover
includes at least one of: at least one electrode alignment tab,
each of said alignment tab having a thickness that is equal to the
gap distance; a plurality of electrical connection holes that are
adapted to receive an electrical connection device; at least one
air trap, each of the at least one air trap being fluidly coupled
to a corresponding slide valve; a plurality of electrode alignment
pin holes that are structured and arranged to be in registration
with a corresponding plurality of alignment pin holes that are
disposed on each end of each of the plurality of electrodes; and a
screw cap for sealing a top of a volume compression chamber.
11. The device as recited in claim 6, wherein the case end cover
includes a volume compression chamber that is filled with a
closed-cell foam.
12. The device as recited in claim 1, further comprising a
controller for controlling the controllable damping system and for
receiving measurement data from the at last one sensing device, the
controller structured and arranged to vary a magnitude of voltage
delivered to an electrode that is electrically coupled to the
damping system or a duration of voltage delivery, said voltage
being adapted to tune the resistivity of the electro-rheological
fluid, to provide a desired isokinetic or isotonic response.
13. The device as recited in claim 1, wherein the at least one
electrode includes an central bore electrode, a middle electrode,
and an outer electrode.
14. The device as recited in claim 13, wherein the central bore
electrode has a negative polarity, the middle electrode has a
positive polarity, and the outer electrode has a negative
polarity.
15. The device as recited in claim 13, wherein each of said at
least one electrode has a height and the height of the middle
electrode is less than the height of the central bore and outer
electrodes.
16. The device as recited in claim 15, wherein a spacer is provided
for fine tuning the damping system.
17. The device as recited in claim 11, wherein the closed-cell foam
is buna-based or a neoprene-based closed-cell foam.
18. The device as recited in claim 12, wherein the controller is
adapted to provide an isotonic or isokinetic motion to the movable
handle portion.
19. The device as recited in claim 12, wherein the controller is
adapted to account for any Stribeck effect.
20. The device as recited in claim 1, the at least one electrode
being a single electrode and the damping system further comprising
a choke assembly having a through hole through which the
electro-rheological fluid is forced from the damping chamber to a
volume compression chamber and vice versa.
21. The device as recited in claim 1, the device having a rolling
diaphragm seal to provide a rolling seal.
22. The device as recited in claim 1 further comprising a second,
spring-biased piston that is structured and arranged to act in an
opposite direction as the damping piston.
23. The device as recited in claim 21, wherein an
electro-rheological fluid valve is disposed between the damping
piston and the spring-biased piston.
24. The device as recited in claim 23, wherein the
electro-rheological fluid valve includes plural positive polarity
members and plural negative polarity members.
25. A rotary damping system for providing a braking action using an
electro-rheological fluid, the system comprising: a body having a
first, upper portion and a second, lower portion made from an
electrically non-conductive material; a first plurality of positive
polarity electrodes having a variable first gap distance between
adjacent negative polarity electrodes; a second plurality of
negative polarity electrodes having a variable second gap distance
between adjacent positive polarity electrodes; the upper portion of
the body structured and arranged to accommodate the first
plurality, which are rotatable, and the lower portion of the body
structured and arranged to accommodate the second plurality, which
are stationary, the first plurality being disposed within the gap
between adjacent negative polarity electrodes, and the second
plurality being disposed within the gap between adjacent positive
polarity electrodes; and a safe high voltage connection that is
electrically coupled to a voltage source and to the plurality of
first plurality of positive polarity electrodes.
26. The system as recited in claim 25, wherein each of the first
plurality of positive polarity electrodes are substantially hollow
cylinders that are coaxial and concentric to one another.
27. The system as recited in claim 25, wherein each of the second
plurality of negative polarity electrodes are substantially hollow
cylinders that are coaxial and concentric to one another.
28. The system as recited in claim 25, wherein each of the first
and second pluralities of electrodes has a height, and the height
of the first plurality differs from the height of the second
plurality.
29. The system as recited in claim 25 further comprising an
electrically-conductive, elongate body that is mechanically coupled
to the first plurality of positive polarity electrodes.
30. The system as recited in claim 25 further comprising a
controller for selectively controlling a voltage delivered to the
first plurality of positive polarity electrodes, to activate the
electro-rheological fluid between adjacent positive and negative
polarity electrodes to cause the system to brake.
31. A system for providing a controllable velocity or resistive
force during exercises of a mammalian extremity, the system
comprising: variable resistance hand rehabilitation device
including: a support structure for providing strength and structure
to the device; a handle portion by which the extremity performs the
exercises through translating in a single degree of freedom; a
controllable damping system that is structured and arranged to
provide a selectively controlled resistance to the extremity using
an electro-rheological fluid having a resistivity that is
continuously variable throughout a stroke cycle; at least one
sensing device, each of which is mechanically coupled to the handle
portion and each of which is adapted to provide measurement data
for controlling the resistivity of the electro-rheological fluid;
and a controller for controlling the controllable damping system
and for receiving measurement data from the at last one sensing
device, the controller structured and arranged to vary current flow
to an electrode that is electrically coupled to the damping system,
said current being adapted to tune the resistivity of the
electro-rheological fluid, to provide a desired isokinetic or
isotonic response.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present utility patent application claims the benefit of
priority to U.S. Provisional Patent Application No. 61/130,484
dated May 30, 2008 entitled "Variable Resistance Hand
Rehabilitation Device With Linear Smart Fluid Damper And Dynometer
Capabilities".
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] (Not applicable)
BACKGROUND OF THE INVENTION
[0003] A device for hand rehabilitation is disclosed, and, more
particularly, a one degree-of-freedom hand rehabilitation device
that provides controllable resistance during hand-gripping and
hand-releasing exercises and that is compatible with magnetic
resonance imaging (MRI) is disclosed.
[0004] Of the many impairments that result from stroke, perhaps the
most disabling is hemiparesis of the upper limb because the impact
on disability, independence, and quality of life is so marked.
Stroke survivors typically receive intensive, hands-on physical and
occupational therapy to encourage motor recovery. However, due to
economic pressures on the U.S. health care industry, individuals,
post stroke, are receiving less therapy and are being discharged
from rehabilitation hospitals before rehabilitation is
complete.
[0005] Robotic/force feedback training is a considerably new
technology that has shown great potential for application in the
field of neuro-rehabilitation as it has several advantages, e.g.,
motivation, adaptability, data collection, and the ability to
provide intensive individualized repetitive practice. Studies on
robotic/force feedback devices for post stroke upper extremity
rehabilitation have shown significant increases in upper limb
function, dexterity, and fine motor manipulations as well as
improved proximal motor control.
[0006] Furthermore, functional Magnetic Resonance Imaging (fMRI),
which maps brain hemodynamic changes, is being more widely used to
study human brain mechanisms controlling voluntary movement and
reorganization of the sensorimotor brain system in response to
neurological injuries such as stroke. fMRI-compatible devices are
required to study the brain mechanisms of motor performance in
controllable dynamic environments; to enable clinicians to quantify
and monitor the effect of motor retraining in stroke patients; and
to improve the practice of neuro-rehabilitation.
[0007] Due to the nature of fMRI modality, which uses high energy
magnetic fields, fast-switching magnetic field gradients and
radio-frequency pulses, as well as being very sensitive to external
noise, the development and use of MR-compatible devices are very
challenging tasks. Despite these challenges, MR-compatible, force
feedback interfaces have been introduced in the past few years.
Embodiments of these interfaces have included: a manipulandum with
actuators, force and/or motion sensing systems, and tactile
stimulators, all of which enable neurologists to investigate motor
performance and the mechanisms of neural recovery following
neurological injuries such as stroke.
[0008] A force feedback rehabilitation device that can be used in
fMRI studies to allow neurologists or other practitioners to
evaluate patients for changes in brain activity associated with
motor retraining is desirable. Moreover, a compact, force feedback
rehabilitation device that facilitates retraining of hand
grasp/release motor skills in patients recovering from neurological
ailments, e.g., stroke, is also desired.
SUMMARY OF THE INVENTION
[0009] A variable resistance hand rehabilitation device and
corresponding system are disclosed. Improvements over the prior art
include: a new damping system or damper design, to reduce friction
and increase maximum force output; a dynometer feature that enables
converting the dynamic device to a static grip force measuring
device; a closed-loop controller; and a new graphic user interface
for the medical practitioner and new virtual reality game software
that allow accurate and smooth operation of the device and
increased patient motivation.
[0010] A controllable damper is the main component of the device.
The controllable damper is an ERF-based, continuously variable,
computer-controlled damping system that provides smooth resistance
throughout a grip/release stroke cycle. Closed-loop control enables
operational resistance to be isotonic (constant force), isokinetic
(constant velocity), or to follow a predefined force profile.
[0011] The damper employs plural coaxial, concentric, hollow,
cylindrical electrodes that are separated by gaps through which the
ERF can be forced. In the absence of an electric field, the damper
provides virtually zero resistance. However, when voltage is
applied to at least one of the electrodes, an electric field is
generated through the ERF, which results in a change in yield
stress, producing a selectively tunable degree of resistivity.
[0012] The pressure on the piston generated by the ERF valve as
well as the frictional force of a seal combine to form the baseline
force that must be overcome in order for a patient/user to move the
damper's output shaft.
[0013] To accommodate changes in volume within the damping chamber,
a volume compensation chamber filled with closed-cell foam is
provided. The volume compensation chamber (VCC) is filled with a
closed-cell foam that compresses, e.g., elastically, as the output
shaft connected to the damping piston translates back into the
damping chamber during the return stroke. Use of closed-cell foam
is advantageous over traditional volume compensation methods due to
its simplicity, low cost, low spring rate, and durability. The VCC
is further structured and arranged to facilitate evacuating and
eliminating gases from the damping system, to prevent air bubbles
and/or cavitation. A Buna-/Neoprene-based closed-cell foam is
suitable for use due to its compatibility with oils, low spring
rate, and good compression recovery.
[0014] To provide positional feedback to the software controller, a
linear potentiometer is mounted to the moving handle portion. The
linear potentiometer measures displacement of the moving handle
portion. For force measurement, a load cell is mounted to the
moving handle portion, to measure force as it is applied by the
patient/user.
[0015] The device includes a return force control subsystem to
control the level of return force once the patient/user has
completed a stroke cycle. Use of a standard setup protocol that
normalizes the return force to a known reference point, allows an
adjustable, repeatable return force, which enables a practitioner
to setup and repeat experiments/tests under the same or virtually
the same conditions.
[0016] Optionally, the device also may include a dynometer-like
locking mechanism. The locking mechanism is adapted to lock the
output shaft in a desired position. Use of the dynometer changes
the functionality of the device from a dynamic force- or
velocity-controlled device to a static device that measures grip
strength with the handles in any position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention is pointed out with particularity in the
appended claims. However, the advantages of the invention described
above, together with further advantages, may be better understood
by referring to the following description taken in conjunction with
the accompanying drawings. The drawings are not necessarily drawn
to scale, and like reference numerals refer to the same parts
throughout the different views.
[0018] FIG. 1 shows an illustration of a variable resistance hand
rehabilitation device system in accordance with the present
invention;
[0019] FIG. 2 shows an elevation view of a patient-actuated
variable resistance hand rehabilitation device (VRHD) in accordance
with the present invention;
[0020] FIG. 3 shows an isometric view of a first side of a
patient-actuated variable resistance hand rehabilitation device
(VRHD) in accordance with the present invention;
[0021] FIG. 4 shows an isometric view of a second side of a
patient-actuated variable resistance hand rehabilitation device
(VRHD) in accordance with the present invention;
[0022] FIG. 5 shows an illustration of a first joining means for a
handle portion in accordance with the present invention;
[0023] FIG. 6 shows an illustration of a spherical joint for a
handle portion in accordance with the present invention;
[0024] FIG. 7 shows an isometric view of a dynometer locking
mechanism in accordance with the present invention;
[0025] FIG. 8 shows an exploded view of the dynometer locking
mechanism shown in FIG. 7;
[0026] FIG. 9 shows a cross-section view of a damping system,
volume compensation system, and return force control system in
accordance with the present invention;
[0027] FIG. 10 shows a cross-section view of a damping system and
volume compensation system in accordance with the present
invention;
[0028] FIG. 11 shows an isometric view of the plural electrodes in
accordance with the present invention;
[0029] FIG. 12 shows a detail of the air trap and slide valve on
the case end cap in accordance with the present invention;
[0030] FIG. 13 shows the interior (A) and exterior (B) surfaces of
the case end cap in accordance with the present invention;
[0031] FIG. 14 shows the interior (A) and exterior (B) surfaces of
the case manifold in accordance with the present invention;
[0032] FIG. 15 shows a block diagram of an exemplary control
algorithm for a PI controller;
[0033] FIG. 16 shows a representative force versus time graph of a
grip-and-release stroke cycle;
[0034] FIG. 17 shows an embodiment of a miniature damping device
using electro-rheological fluid;
[0035] FIG. 18 shows an illustrative embodiment of a diaphragm
seal-based damping system in accordance with the present
invention;
[0036] FIG. 19 shows a cut-away view of the diaphragm seal-based
damping system of FIG. 18;
[0037] FIG. 20 shows isometric (A) and front elevation views (B) of
an electro-rheological valve used in the damping system of FIG.
18;
[0038] FIG. 21 shows a diagram of a diaphragm seal and piston for
use with the damping system of FIG. 18;
[0039] FIG. 22 shows a first plurality of rotatable electrodes and
a second plurality of stationary electrodes; and
[0040] FIG. 23 shows cross-sectional views of a portable,
rotary-type electro-rheological fluid-based brake that includes the
electrodes of FIG. 22.
DETAILED DESCRIPTION OF THE INVENTION
[0041] A Variable Resistance Hand Rehabilitation Device (VRHD) and
a system using the VRHD are disclosed. The VRHD is a
patient-actuated device adapted for isotonic, isokinetic, and/or
variable resistance grasp and release exercises for mammalian
extremities, e.g., the human hand. Its principal functionality is
derived from an electro-rheological fluid-based controllable
damping system (or damper) that allows continuously variable
modulation of dynamic resistance throughout its stroke. Indeed, a
desirable feature of the device is the use of electro-rheological
fluids (ERF) to achieve tunable, computer controlled, resistive
force generation. For this purpose, a change in yield stress
observed in an ERF in response to an electric field can be
exploited to produce virtually zero resistance when idle and
selectively-tunable resistivity when an electric field is applied
to the ERF.
[0042] The VRHD is an improvement of a controllable damper that is
the subject of U.S. patent application Ser. No. 11/886,342 commonly
owned by Northeastern University of Boston, Mass. and included
herein in its entirety by reference. The VRHD of the current
invention, however, provides a resistive force for grasp and
release hand exercises that is controllable, repeatable, and
quantifiable.
[0043] Referring to FIG. 1, a hand rehabilitation system 10 is
shown. The system 10 includes a patient-actuated device, i.e., a
VRHD 2; control electronics 4, e.g., control hardware and
corresponding control software, for controlling delivery of a
desired force or velocity to the patient/user; a high-voltage power
supply 6; and a software interface 8, e.g., a graphical user
interface (GUI) and virtual reality (VR) game software, for
displaying acquired patient data during manipulation or operation
of the VRDH 2.
[0044] The power supply 6 provides power to the patient-actuated
device 2 via a first voltage bus 1 and to the low-level control
electronics 4 via a second voltage bus 9.
[0045] The control electronics 4 are in electrical communication
with the patient-actuated device 2, to receive measurement data
signals from at least one sensing device and to provide control
signals thereto; as well as with the software interface 8, which
can be disposed local to or remote from the patient-actuated device
2 and/or the control electronics 4.
[0046] The patient-actuated device 2 includes, inter alia, a
sensing system and communication means 7 for transmitting
measurement (data) signals to the control electronics 4, e.g., via
radio frequency (RF) signals and/or via hardwire communication. The
control electronics 4 include means for reformatting, processing,
and filtering the data signals and means for transmitting the
processed data 7 to a local or remote processor 5, e.g., a personal
computer or microprocessor, that is electrically connected through
the software interface 8, e.g., via RF signals of via hardwire
communication.
[0047] The hardware of and/or software executable on the processor
5 is/are adapted to store in memory and/or to display the data from
the control electronics 4 on a display device 3, e.g., a computer
screen or monitor, that is electrically coupled to the processor 5.
The data display 3 can take any shape or form desired by the
practitioner or the patient/user.
Patient-Actuated Device
[0048] The patient-actuated, variable resistance hand
rehabilitation device (VRHD) includes significant improvements over
a system described in U.S. patent application Ser. No. 11/886,342,
chief of which includes replacement of a rotary brake design
details with a linear system. Linear handle motion, e.g., using a
linear, electro-rheological fluid-based (ERF-based) damper,
provides significant advantages to the rotary brake design. For
example, a linear ERF-based damper is capable of generating larger
resistive forces compared to a similarly sized rotary ERF damper.
Moreover, increased resistive force output eliminates the need for
gears. Elimination of gears reduces mechanical friction associated
with the device, which translates into a much smaller zero voltage
resistance. Furthermore, design is simpler, stronger, and includes
fewer parts.
[0049] Linear translation of a moving handle portion (as opposed to
rotary handle motion) greatly simplifies direct force measurement
using a linear force sensing device, e.g., a load cell, that is
disposed proximate the moving handle portion. In contrast, with a
rotary brake, output rotary torque is extrapolated dimensionally
using force measurements from two compression sensing devices and a
known moment arm. Direct force measurement reduces systematic
errors, which increases repeatability, simplifies related software
algorithms, and reduces the quantity of sensors needed by one.
[0050] Referring to FIGS. 2-4, an embodiment of a patient-actuated
VRHD 2 is shown. The VRHD 2 includes a support structure 16, a
handle portion 20, a sensing system 50, a handle return force
control system 17, a (dynometer) locking system 15, a controllable
damping system 30, and a volume compensation system 40. The design
of the present invention focuses on optimizing the linear system
described in U.S. patent application Ser. No. 11/886,342.
[0051] To use the device, a patient/user would grasp the handle
portion 20, which is at an at-rest, open position, and squeeze,
exerting a rearward force or pressure on the moving handle portion
21. The damping system 30 modulates the resistance of the moving
handle portion 21 to a preset level throughout the stroke cycle.
After the stroke is complete, the damping system 30 deactivates and
the handle return force control system 17 returns the handle back
to the at-rest, open position.
[0052] The support structure 16 is configured and arranged to
provide integrity to and support each of the other portions or
sub-systems that make up the VRHD 2 so as to enhance the proper
functioning and operation of each of the other portions or
sub-systems as described in greater detail below. Those of ordinary
skill in the art can appreciate that there exists a myriad of
different structural support schemes, hence, the precise form of
the support structure 16 is less important than the function it
performs.
[0053] The support structure 16 for the embodied VRHD 2 disclosed
herein includes a pair of horizontal support portions 16a that are
rigidly connected by a pair of support brackets 16b and 16c. The
pair of horizontal support portions 16a are elongate members such
as rods and, more particularly, cylindrical rods. Each bracket of
the pair of support brackets 16b and 16c is attached orthogonally
or substantially orthogonally to the horizontal support portions
16a and are positioned and arranged to maintain each of the support
portions 16a parallel or substantially parallel to one another in a
horizontal or substantially horizontal plane.
[0054] According to the illustrative embodiment described herein, a
first support bracket 16b is disposed proximate to the locking
mechanism 15. A second support bracket 16c is disposed so as to be
releasably attached to the damping system 30. More detailed
description of the support structure 16 is provided below in the
description of the operation of the VRHD 2.
[0055] The handle portion 20 of the VRHD 2 includes a first, moving
handle portion 21 and a second, stationary handle portion 22,
which, preferably, include ergonomic designs to conform to a human
hand, to provide maximum user comfort. The moving handle portion 21
includes a first opening 23 and a second opening 24 that are each
sized to accommodate low-friction, linear, plain bushings 29 and
the elongate portions 16a the support structure. The bushings 29,
e.g., a low-friction, linear, plain bushing manufactured by Igus
Limited of Northampton, England, enable the moving handle portion
21 to translate linearly with respect to and along the
corresponding elongate portions 16a with minimal frictional
resistance between the bushings 29 and the peripheral surfaces of
the openings 23 and 24 and/or with the corresponding elongate
portions 16a of the support structure.
[0056] As shown in FIG. 5, optionally, a handle position adjusting
device 26, e.g., a nut/bolt combination, can be provided in the
handle portion 20 for adjusting the relative positions of the
handle portion 21 and the stationary handle portion 22.
[0057] The moving handle portion 21 is mechanically coupled to a
sensing system 50, which can include, for example, a strain
gauge-based load cell 12 and a linear potentiometer 11. The stain
gauge-based load cell 12, e.g., a 150-lb. load cell manufactured by
Interface Force Measurements Limited of Berkshire, England, is
adapted to measure force applied to the moving handle portion 21 by
the patient/user directly. The linear potentiometer 11, e.g., a
custom linear potentiometer manufactured by Active Sensors, Inc. of
Indianapolis, Ind., is structured and arranged to measure the
absolute position of the moving handle portion 21.
[0058] Data from the sensing system 50 are transmitted to the
controller 4 in real-time. The controller 4 uses the data for
closed-loop control of the VRHD 2 and, furthermore, processes these
data and transmits the processed data in a suitable format for
displaying real-time performance information at the software
interface 8 and/or for storing the data, so that said data can be
viewed and analyzed at a later time by a researcher.
[0059] The strain gauge-based load cell 12 is attached to or
mechanically mounted on the moving handle portion 21 and is
releasably attached to an output shaft 39 of a piston (not shown)
associated with the damping system 30 or an extension thereto
and/or to a handle adjusting device 26. Wires (not shown) and/or a
radio frequency (RF) device (not shown) are provided to
electrically couple the strain gauge-based load cell 12 to the
controller 4 so that measurement data from the load cell 12 can be
transmitted to the controller 4 in real-time.
[0060] The linear potentiometer 11 can also be mechanically
attached to the moving handle portion 21 and to one of the fixed
brackets 16b of the support structure. As shown in FIG. 3, a
proximal end of the linear potentiometer 11 can be inserted in a
notched area 14 provided for that purpose in the bracket portion
16b of the support structure and a distal end of the linear
potentiometer 11 can be fixedly or releasably attached to the
moving handle portion 21, e.g., using machine screws, machine
bolts, rivets, and the like 27. Wires (not shown) or an RF device
(not shown) are provided to electrically couple the linear
potentiometer 11 to the controller 4 so that measurement data from
the potentiometer 11 can be transmitted to the controller 4 in
real-time. To minimize electro-magnetic interference (EMI) when
used in connection with MRI, all wires should be shielded.
[0061] As shown in FIG. 5 and FIG. 6, the strain gauge-based load
cell 12 and/or the handle position adjusting device 26 can be
releasably attached to the moving handle portion 21 using a nut and
bolt combination 27 (FIG. 5) or using a spherical joint 49 (FIG.
6).
[0062] As shown in FIGS. 2-4, the handle portion 20 can include a
removable stroke length scale 28 and handle motion stops 25. The
stroke length scale 28 can be removably attached, e.g., clipped on,
to an elongate portion 16a of the support structure, to provide a
visual measure of stroke lengths. The adjustable handle motion
stops 25 can be used to delineate the limits of the stroke of the
moving handle portion 21, which allows the patient/user or medical
practitioner to adjust the start point and end point of each stroke
cycle, to accommodate varying patient/user needs.
[0063] Each of the pair of adjustable handle motion stops 25
comprises adjustable shaft collars that are disposed on and
releasably attachable to one of the elongate portions 16a of the
support structure, upstream and downstream of the direction of
travel of the moving handle portion 21. The locations of these
shaft collars can be set with some precision using the removable
stroke length scale 28. Although the adjustable handle motion stops
25 are shown on the upper elongate portion 16a, those skilled in
the art can appreciate that adjustable handle motion stops 25 could
also be disposed on the lower elongate portion 16a.
[0064] The handle return force control system 17 controls speed of
the moving handle portion 21 back to the start point of the stroke
length after the patient/user has released or reduced the force on
the moving handle portion 21 by modulating the elastic force with
sliders 18 and a notched scale 34. The handle return force control
system 17 is implemented as an elastic-based return system.
[0065] As shown in FIGS. 2-4, the handle return force control
system 17 includes a pair of tubes 31, a pair of slidable elastic
mounts 18, and a pair of notched scales 34. Each of the pair of
tubes 31, e.g., surgical silicone tubes, is releasably attached,
e.g., using ferrules 13, at a distal end to a bracket 32 mounted
proximate to the strain gauge-based load cell 12 so that when the
patient/user applies force to the moving handle portion 21, the
bracket 32 applies force to the ferrules 13 and to the tubes 31,
elastically displacing the tubes 31.
[0066] The other, proximal ends of the tubes 31 are each releasably
attached to a corresponding, selectively positionable slidable
elastic mount 18. Each of the sliding elastic mounts 18 is
structured and arranged to control the preload of each tube 31.
More specifically, each slidable elastic mount 18 controls the
preload of each tube 31 using the mount's selectively fixed
location, e.g., at a discrete positioning notch, on a corresponding
notched scale 34.
[0067] Each of the notched scales 34 includes an inner opening into
which one of the elongate portions 16a of the support structure can
be inserted, much like a grip on a bicycle handle bar. Each
slidable mount 18 is structured and arranged to mate with a
positioning notch on a corresponding notched scale 34. The
functioning and interoperability of the handle return force control
system 17 will be described in greater detail below.
[0068] The (dynometer) locking system 15 is a locking mechanism
that is structured and arranged to lock the output shaft 39 into a
pre-designated position, to change the functionality of the VRHD 2
from a dynamic measuring device to a static measuring device. The
purpose of the locking system 15 is to prohibit movement of the
output shaft 39 in a linear or a rotational direction. As a result,
during static use, any force applied by the patient/user to the
moving handle portion 21 produces data at the strain gauge-based
load cell 12 that can be used to determine a patient's/user's
maximum and sustained manual squeezing.
[0069] An illustrative embodiment of a locking system 15 is shown
in FIG. 7 and FIG. 8 in an assembled and in an exploded view,
respectively. Under normal, dynamic measuring conditions, the
locking mechanism 15 does not impact the operation of the output
shaft 39 with respect to the handle portion 20. However, when
static measurements are desired, the locking mechanism 15 can be
activated so that force applied to the moving handle portion 21 is
not transmitted to output shaft 39 and/or the damping piston
35.
[0070] When static measurement functionality is desired, the
locking mechanism 15 is engaged by applying a radial force (torque)
to a lever 19 that can be inserted in and/or that protrudes from
the outer periphery of the locking mechanism 15. The lever 19 acts
as a moment arm to engage the locking mechanism. The locking
mechanism includes a portion that is fixed to the structure
support, a second portion that is screwed to the support structure
with a course thread, and a plastic wedge that is forced against
the output shaft when the second portion is tightened.
[0071] The locking force is directly related to the amount of
torque applied to the lever 19 of the locking mechanism 15.
Reversing the direction of this force will release the locking
mechanism 15 so that the output shaft 39 will move freely. Because
the locking system 15 is located between the load cell 12 and the
damping piston (not shown), the force applied to the first handle
portion 21 by the patient/user can also be read into the software.
This functionality mimics that of a standard Hand Dynometer.
[0072] A controllable damping system 30 is shown in FIGS. 9-12. The
controllable and tunable damping system 30 includes an air- and
water-tight protective outer case and internal damping component.
The working (damping) components of the controllable damping system
30 include a plurality of concentric and coaxial electrodes 33, 37,
and 38, a piston 35, and an output shaft 39. Briefly, during
operation, voltage is delivered to a middle electrode 37 to
generate an electric field in the ERF between the middle electrode
37 and each of the central bore 33 and outer electrodes 38. The
electric field affects the yield stress of the ERF, causing the ERF
to thicken as it is activated. As the EFR thickens, it becomes more
resistive to flow, increasing the overall resistivity of the damper
30 and making it more difficult for the piston 35 to force the ERF
through the gaps 43.
[0073] The plurality of electrodes 33, 37, and 38 are hollow
cylinders that, preferably, are manufactured from a thermally- and
electrically-conductive material, such as aluminum. Although the
drawings show three concentric and coaxial electrodes, this is done
for illustrative purposes only. Theoretically, one or more
electrodes could be used.
[0074] The plurality of electrodes includes a central bore
electrode 33, which has a negative (n) (or ground) polarity, a
middle electrode 37, which has a positive (p) polarity, and an
outer electrode 38, which also has a negative (n) (or ground)
polarity. Fluid gaps 43, whose purposes is described in greater
detail below, are provided between the middle electrode 37 and each
of the central bore 33 and outer electrodes 38. The gap 43 is
between approximately 0.5 mm and 1.5 mm, depending on the
application.
[0075] Each of the plurality of electrodes 33, 37, and 38 can have
the same height. Alternatively, to provide additional means for
adjusting the maximum and minimum force capabilities of the damper
30, the height of the middle electrode 37 can be adjusted, i.e.,
shortened with respect to the central bore 33 and outer electrodes
38. Shortening the middle electrode 37 will confine or limit the
extent of the magnetic field generated by the electrodes only to
the shortened length of the middle electrode 37. This will cause
the resistivity to decrease. Consequently, the minimum, i.e.,
baseline, resistive force of the VRHD 2 and the maximum force of
the VRHD 2 will decrease.
[0076] If the height of the middle electrode 37 is shortened, a
spacer, e.g., a plastic spacer, can be added to fill the additional
space between the electrode 37 and the case end cap 44. Accordingly
and advantageously, by modifying the length of the middle electrode
36, the resistivity provided by the damper 30 can be fine tuned for
any desired application.
[0077] Electrical connection to each of the electrodes 33, 37, and
38 is made via electrically-conductive socket head cap screws or
bolts, which are removably attached to each of the electrodes. As
shown in FIG. 11, each of the plurality of electrodes 33, 37, and
38 includes a tapped electrical connection screw hole 58c into
which the socket head cap screw or bolt can be inserted. FIG. 13
shows corresponding electrical connection holes 58a and 58b that
are provided in the end cover cap 44 that are structured and
arranged to be in registration with the tapped electrical
connection screw holes 58c on each of the plurality of electrodes
33, 37, and 38. The pair of screw holes 58a in the end cover cap 44
are electrically coupled to the negative (n) (ground) pole and the
single screw hole 58b is electrically coupled to the positive (p)
pole.
[0078] Referring to FIG. 10, an electrically-conductive metal,
e.g., aluminum, screw or bolt (not shown) is disposed through and
into each of the screw holes 58a or 58b and 58c. An
electrically-conductive wire (not shown) is coupled to a protruding
end or head of the metal screws or bolts, e.g., using an eyelet.
The electrically-conductive wire is further attached to a rod 57
that is mounted within an electrically-conductive metal, e.g.,
aluminum, adapter 61.
[0079] An electrical (female-type) connection or wire 62, e.g., a
high-voltage panel connector such as those manufactured by
Teledyne-Reynolds of Berkshire, England or ODU-USA of Camarilla,
Calif., is electrically coupled to the metal adapter 61. The
connector 62 is adapted to use the non-electrically conductive
damping case as ground and to use a central pin 63 as a positive
cathode. A mating (male-type) connector (not shown) is electrically
coupled between the end portion of a coaxial wire extension from
the female-type connection 62 and the high voltage power supply 6
(FIG. 1). The electrical connections preferably deliver
low-amperage current to minimize any impact on the MRI machinery
and electronics.
[0080] The concentric and coaxial electrodes 33, 37, and 38 are
confined within a protective damper case that includes a center
case 45, a removable case end cover or cap 44, and a case manifold
42. Mounting the electrodes within a damper case having a removable
case end cover 44 allows easy access to the electrical connections
without having to drain the ERF from the damping system 30.
[0081] The protective damper case can be made out of any
electrically-insulative, i.e., non-conductive, material and is
precision machined to maintain system concentricity. Preferably,
each of the component parts of the protective damper case is
manufactured of an insulative polymer such as polyoxymethylene
(POM), e.g., Delrin.RTM. manufactured by DuPont.
[0082] As shown in FIG. 10 and FIG. 12, the outer periphery of the
outer electrode 38 is in a tight interference fit with the inner
peripheral surface of the center case 45. The protective damper
case is completed by the case end cap 44 and the case manifold 42,
which are releasably secured to the end portions of the center case
45, e.g., using machine or industrial screws or bolts and the like.
Although the drawings show that the interior and exterior
peripheral surfaces of the case center 45 and the outer peripheral
surface of the outer electrode 38 are cylindrical, this is shown
for illustrative purposes only. The peripheral surfaces could,
alternatively, be polygonal.
[0083] Referring to FIG. 13 and FIG. 14, interior faces (A) and
exterior faces (B) of an embodiment of a case end cap 44 and of a
manifold 42, respectively, are shown. The interior faces (A)
correspond to the portions of the case end cap 44 and of the case
manifold 42 that interface with the center case 45 to form the a
sealable damping system 30. The exterior faces (B) correspond to
the portions of the case end cap 44 and of the case manifold 42
that are exterior to the damping system 30.
[0084] The case end cap 44 and the case manifold 42 each include a
plurality of mounting holes 47 that are arranged to be in
registration with corresponding pluralities of mounting openings 47
disposed on both end portions of the wall of the center case 45.
The mounting holes/openings 47 are adapted to receive a fastening
device (not shown), e.g., a machine screw or bolt, a socket-type
screw of bolt, and the like, for releasably securing the center
case 45 to each of the case end cap 44 and the case manifold 42, to
provide an air- and water-tight damping chamber 36
therebetween.
[0085] The interior faces (A) of each of the case end cap 44 and of
the case manifold 42 include a gland 51, a plurality of electrode
alignment tabs 46, and a pin hole alignment portion 48b. The gland
51 is adapted for retaining an annular sealing device (not shown),
e.g., an O-ring. Moreover, the gland 51 is dimensioned to be in
registration with the wall section of the center case 45 so that
the wall section forms an air- and water-tight seal when pressed
against the annular sealing device.
[0086] Each of the plurality of electrode alignment tabs 46
includes a first tab 46a and a second tab 46b. The first tab 46a is
precision machined to provide and to maintain the gap 43 between
the outer electrode 38 and the middle electrode 37. The second tab
46b is precision machined to provide and to maintain the gap 43
between the central bore electrode 33 and the middle electrode 37.
The electrode alignment tabs 46a and 46b keep the electrodes
aligned precisely, so that the dimensions of the gaps 43 between
them are constant and, more particularly, so that the central bore
electrode 33 remains concentric and coaxial with respect to piston
35, to minimize friction therebetween.
[0087] The alignment pin holes 48b are also provided to properly
align the electrodes within the protective damper case. More
particularly, during assembly, alignment pin holes 48a disposed on
the end portions of each of the electrodes 33, 37, and 38 are
placed in registration with the alignment pin holes 48b. Alignment
pins or screws (not shown) are inserted through the alignment pin
holes 48b in the case end cover 44 and in the electrode alignment
pin holes 48a, to fix the electrodes 33, 37, and 38 in place.
[0088] The interior face (A) of the case end cap 44 (FIG. 13) also
includes plural air traps 54 and a volume compensation chamber 53,
which will be described in greater detail below. Each of the air
traps 54 is fluidly connected via a fluid conduit 65 to a
corresponding slide valve 64. The slide valves 64 are provided to
facilitate draining any air/gas that collects in the air traps 54
prior to and during the filling operation and/or during operation
of the damper 30. As is well-known, air/gas has a significantly
lower dielectric strength then ERF. Accordingly, any gas bubbles
whose dimensions equal the gap 43 distance could induce arcing
between adjacent electrodes. These features also allow the damping
system 30 to be slightly pressurized to prevent cavitation and
allow the damper 30 to operate in any orientation.
[0089] The interior face (A) of the case manifold 42 (FIG. 14)
includes an opening 52 that is structured and arranged to
accommodate the output shaft 39. The exterior face (B) of the case
manifold 42 includes a gland 59 or groove. The gland 59 is
concentric and coaxial with the opening 52 and with the output
shaft 39. The gland 59 is adapted to retain an annular sealing
device.
[0090] Preferably a Teflon-based, spring-loaded sealing device 56
is disposed within the seal gland 59 (FIG. 10), about the output
piston 39. The spring-loaded sealing device 56 prevents fluid
leakage and is custom designed for each application depending on
whether low friction or, alternatively, durability is desirable.
The sealing device 56 can be made up of three parts (not
shown).
[0091] First, a stationary, flanged-nut having an external male
thread can be mounted onto a base-plate. This first part is
machined with a female tapered bore through which the shaft 39
traverses freely. Second, a Teflon.RTM. annular ring having a
split-male taper with a slip that is dimensioned to that of the
shaft 39, is mated with the taper of the stationary flanged-nut.
Finally, the locking nut having an internal thread, is mated with
the stationary-flanged nut. The locking nut also includes a through
bore through which the shaft 39 traverses freely.
[0092] The locking nut contains, aligns, and compresses the Teflon
taper, to create resistance along the peripheral surface of the
shaft 39. The split-male taper is subsequently secured to a locking
nut for release purposes. The magnitude of the torque applied to
the shaft 39 determines the resistance to axial and radial
movement
[0093] The piston 35 is machined to provide a radial clearance
between approximately 0.002 in. and approximately 0.005 in. between
the outer diameter of the piston 35 and the inner diameter of the
central bore electrode 33. This close clearance eliminates friction
associated with normal piston seals and reduces pressure leakage to
a negligible amount. The inner peripheral surface of the central
bore electrode 33 as well as the outer peripheral surface of the
piston 35 also can be hard coated, e.g., with a low-friction,
anodized material, to reduce friction if the piston 35 were to rub
against the inner peripheral surface of the central bore electrode
33. Optionally, an annular sealing device (not shown) could be
included in the outer periphery of the piston 35 to provide a tight
seal between a first chamber 36a and a second chamber 36b.
[0094] A volume compensation system 40 is adapted to the damping
system 30, and, more particularly, to the case end cap 44, for
filling and draining the damper 30 but, more pertinently, to
accommodate any change in volume inside the damping system 30 that
results from temperature fluctuations and/or from the operation of
the output shaft 39 and piston 35. The volume compensation system
40 includes a volume compensation chamber (VCC) 53, which is filled
with an elastic, closed-cell foam, a screw cap 67, and a sealing
device 68, e.g., an O-ring.
[0095] Preferably, the VCC 53 is filled with an elastic,
closed-cell foam (not shown) such as Buna or neoprene, which is
naturally adapted to accommodate a change in volume associated with
movement of the output shaft 39 in and/or out of the damper chamber
36. Buna- and/or neoprene-based closed-cell foam is preferred for
use due to its compatibility with oils, its low spring rate, and
its good compression recovery.
[0096] The foam can be formed or tailored into any desired shape,
e.g., cylindrical, polyhedral, and so forth, so that it tightly
fits into the VCC 53. Small ledges or ridges (not shown) can be
added to the inner peripheral surface of the VCC 53, to provide
some frictional resistance, to restrict or restrain the foam from
moving. Optionally, the foam can extend out from the limits of the
VCC 53 into the upstream portion 36b of the damper chamber 36. By
extending the closed-cell foam, the amount of compressible volume
of the foam would increase, however, the stroke length of the
damper 30 would be reduced.
[0097] After closed-cell foam is inserted into the VCC 53, any air
entrained in the closed-cell foam and/or in the damper chamber 36
should be evacuated before the damper chamber 36 is filled with an
additional volume of ERF used to pressurize the damping system 30.
Pressurization prevents degassing of the ERF and, furthermore,
allows the damping system 30 to be operated in any orientation.
Closed-loop Controller
[0098] A typical grasp and release exercise consists of either an
isokinetic (constant speed) or an isotonic (constant force) motion.
Although a closed-loop controller 4 for the invention as claimed
will be described in terms of an isotonic (constant force)
exercise, this is done for the purpose of conciseness rather than
limitation.
[0099] A major challenge in implementing a force-control algorithm
in an ERF-based control device such as the VRHD 2, is that the VRHD
2 can only resist and, as a result, does not produce any "active"
force. However, the VRHD 2 must, on occasion, also act as a brake
in order to input a disturbance in the human motor loop so as, in
the end, to finally exhibit a constant force. In short, the human
being or other mammal must be capable of applying the force to the
moving handling portion 21.
[0100] For example, suppose that during an isotonic exercise, it is
desired that the force applied by the patient must, at all times,
remain less than or equal to a pre-established force value,
F.sub.d. Initially, the applied force is zero, the velocity is
zero, and device 2 remains at-rest. By design, as force is applied,
as long as the applied force remains less than F.sub.d, the VRHD 2
continues to remain at-rest. However, Newtonian physics and the
laws of force, impulse, and momentum provide that as force is
applied and as the VRHD 2 begins to translate, the force necessary
to be applied by the patient/user to keep the VRHD 2 in motion
decreases.
[0101] Problematically, with an isotonic system in which force
remains constant, were the controller 4 to react too quickly to
counteract any decrease in applied force, e.g., by countering the
decrease in applied force by increasing the resistive force that
the patient/user experiences, displacement of the VRHD 2 may stop
altogether. Accordingly, it is desirable to take into account the
Stribeck effect, which is well-known to those of ordinary skill in
the art.
[0102] Referring to the block diagram of an exemplary, PI
controller for isotonic exercises shown in FIG. 15, the force,
F.sub.d, corresponds to the desired force that is pre-set by the
practitioner. The "measured force" and "measured velocity" are,
respectively, the force and velocity measured and/or determined
using data accumulated by the sensing devices. Zeros are respected,
meaning that if all the inputs are zero (in natural units) then the
output voltage 74 that is actually applied to the VRHD 2 equals
zero Volts (0 V).
[0103] The feed-forward term 78, the proportional (P) force gain
(K.sub.p) 71, and the integral (I) force gain (K.sub.i) 76, can be
computed as non-linear functions of the position (or displacement),
the velocity, and the desired force. Integral control with
anti-windup has been investigated for the force loop.
[0104] The proportional force gain term (K.sub.f) 71 changes the
output such that it remains proportional to the force error value,
i.e., the difference between the measured force and the desired
force, F.sub.d, at the force-error summation node 60. In other
words, the proportional response is adjusted merely by multiplying
the force error value 60 by the force gain constant 71,
K.sub.f.
[0105] The integral term 75, which is subsequently added (at
summation node) 66 to the proportional term 69, accelerates the
movement of the process towards a set-point and eliminates the
residual steady-state error that occurs with a proportional only
controller.
[0106] The magnitude of the contribution of the integral term 75 to
the overall control action is determined by the integral gain 76,
K.sub.i. Integral anti-windup ensures that the integral 75
maintains a proper value, avoiding output voltage saturation.
[0107] The feed-forward term 78, V.sub.model, was calculated
experientially from open-loop testing using the equation:
V.sub.model=0.027*F.sub.d+0.29
The V.sub.model term 78 generates the output voltage to the ERF
linearly as a function of the input desired force, F.sub.d. A
damping factor 81 could also be used to control the system, to take
into account the velocity dependence of the force generated by the
system.
[0108] The control saturation term 74 corresponds to the high and
low limit of the output voltage sent to the ERF.
[0109] To improve the performance of the PI Controller, gain
scheduling was used, whereby individual gains were calculated for
different intervals of force. After the stroke cycle is complete
the damper 30 deactivates and the mechanical handle return force
control system 17 brings the first handle portion 21 back to its
at-rest, open position.
[0110] Several experiments using open-loop control of a VRHD, in
which no control action was applied, were performed. The output
force applied by the hand device, however, exhibited great
variability, indicating a greater need for a closed-loop
controller. During initial experimentation with the VRHD 2 using
closed-loop force control, at the beginning of the stroke cycle, a
small overshoot in the force manifests due to the transient from
static to dynamic. To reduce this small overshoot, at the beginning
of the stroke, the command voltage sent to the ERF can be ramped as
a function of the stroke. Afterwards, the command voltage becomes
the sum of the output from the PI controller and the desired
voltage feed-forward term 78. Consequently, a VRHD 2 under
closed-loop force control with the correction voltage in the
beginning of the stroke eliminates the overshoot.
[0111] Three different control hardware configurations have been
used to implement the control algorithm: a Field-Programmable Gate
Array (FPGA) System; a Data Acquisition (DAQ) System, and a
Real-Time (RT) System.
Operation of the VRHD and the VRHD System
[0112] Having described the structural elements of the present
system 10, the operation and interoperability of this structure and
of the VRHD 2 and the VRHD system 10 will now be described. Before
the system 10 can be operated, however, it is important to properly
prepare, i.e., fill, bleed, and pressurize, the damping system 30
with an electro-rheological fluid (ERF).
[0113] Filling the damper 30 is accomplished by first removing the
screw cap 67 of the volume compensation system 40 and removing the
closed-form foam contained therein. The exposed damper chamber 36
can then be filled with an appropriate ERF. After the level of the
ERF reaches the bottom of the volume compensation chamber (VCC) 53,
the closed-form foam is replaced in the VCC 53 and the screw cap 67
is replaced on the volume compensation system 40.
[0114] Due to the deleterious effect of air bubbles within the ERF,
the damping system 30 should be bled. As previously described, air
bubbles can result in arcing between electrodes or have other
deleterious effects on operation of the damping system 30.
[0115] To bleed off any bubbles that may cause arcing, the piston
35 can be cycled several times within the damper chamber 36 while
the slide valve(s) 64 that is fluidly coupled to one of the air
traps 54 is open to the atmosphere and physically located at the
highest elevation with respect to the damper chamber 36 as
possible.
[0116] During a downward (compression) stroke, the piston 35 moves
farthest away from air traps 54 and the least amount of the shaft
39 is contained in the damper chamber 36. Any air trapped in the
damper chamber 36 or in the ERF will bleed out of the slide valve
64.
[0117] When all the air/gas has been bled out and nothing but ERF
exits from the slide valve 64 during a compression stroke, a
syringe containing additional ERF can be placed in or on the slide
valve 64 and a small amount of ERF can be added back into the
damping system 30, to slightly pressurize the system. The damping
system 30 is then ready for operation.
[0118] With the damping system 30 ready to operate, as a
patient/user grips the moving handle portion 21 and applies a force
to the moving handle portion 21, the stain gauge-based load cell 12
senses the load (force) and the load potentiometer 11 is adapted to
measure the displacement caused by the force.
[0119] Force on the moving handle portion 21 is transmitted down
the output shaft 39 to the piston 35 in the damping chamber 36,
causing the piston 35 to translate in the same direction as the
exerted force. Referring to FIG. 10, as the piston 35 translates
(in the direction of the arrow), the pressurized ERF is forced from
a high-pressure zone 36a in the damping chamber 36 though a plenum
portion 79 in the case manifold 42 and, subsequently, into the
plurality of concentric gaps 43 between adjacent electrodes 33, 37,
and 38.
[0120] As the ERF travels through the gaps 43 between the
electrodes 33, 37, and 38, the controller 4 signals the power
source 6 to deliver a controlled, voltage to the middle electrode
37. The controlled voltage generates an electric field within the
ERF, causing the yield stress of the ERF to increase, producing,
thereby, greater resistance to further compression. Low-amperage
current is desirable, especially when used in conjunction with MRI
equipment and electronics.
[0121] The actions of the piston 35 and the transmission of the ERF
through the gaps 43 produce a pressure drop, which acts on the
piston 35 in a direction opposite to that of the direction of pull
by the patient/user. As a result, resistivity to piston 35 motion
is transmitted as feedback to the patient/user, which manifests as
a resistance to translation. After the ERF passes along the entire
heights of the electrodes and through the entire lengths of the
gaps 43, it enters a plenum portion 55 of the case end cover 44,
subsequently collecting in a low-pressure zone 36b behind (upstream
of) the piston 35. During the return stroke, after the patient/user
has released his/her grip on the moving handle portion 21, the
fluid path and high- and low-pressure zones are reversed.
[0122] As previously mentioned, the closed-cell, foam-based volume
compensation system 40 is structured and arranged to compensate for
the changes in volume due to changes in temperature and, more
particularly, due to translation of the output shaft 39 and the
accompanying change of volume. During the piston's return stroke
(opposite direction as arrow on shaft), the closed-cell foam in the
volume compensation chamber 53 compresses, to adjust or account for
the added volume of the additional length and volume of shaft 39
within the damping chamber 36. Hence, as the piston 35 continues to
move to the right (as pictured) and more of the shaft 39 enters the
damping chamber 36, the volume compensation chamber 53 compensates
for the volume increase by compressing. When the piston 35 operates
in a compression mode, the closed-cell foam operates in the
opposite manner.
[0123] Current solutions utilized in other devices include:
secondary piston chambers with spring loaded piston, gas filled
secondary chambers, diaphragms, bellows, and the like. In contrast,
the present system's 40 foam-based implantation is simple,
inexpensive, compact, and highly effective. The closed-cell foam is
also easily removed to allow for quick filling and draining of the
damping chamber 36.
[0124] Referring to FIG. 16, performance of a grasp and release
test using the VRHD is represented by a graph of force versus
time.
Miniature ERF Damping System
[0125] Referring to FIG. 17, a miniature ERF damping system using
the aforementioned damping technology will be described. The
damping system 90 was designed for a specific application, i.e., a
damping force of 1.14 N with a compressed length of 1.5 in., and an
extended length of 2.0 in. (hence, a stroke of 0.5 in.), and a
cross-section of 0.5 in. by 0.5 in.
[0126] The mini-damper 90 includes a damping case 110, a single
hollow, cylindrical electrode 92, and a damping piston 91 that is
mechanically coupled to an output shaft 94. The damping case 110
includes, for example, a central case portion 95, a choke assembly
106, a case end cover 107, and a case manifold 105. A sealing
device 108, e.g., a gasket, is provided at the interface between
the central case portion 95 and the a choke assembly 106, between
the choke assembly 106 and the case end cover 107, and between the
central case portion 95 and the case manifold 105.
[0127] The central case portion 95 is manufactured from an
electrically non-conductive material and can have a shape that is
cylindrical, polygonal, rounded polygonal, and so forth.
Preferably, the inner peripheral surface of the central case
portion 95 is cylindrical, but non-cylindrical surfaces are
possible. Particularly, the inner diameter of the inner peripheral
surface is slightly larger than the outer diameter of the electrode
92. More specifically, the inner diameter of the inner diameter of
the (cylindrical) central case portion 95 is larger than the outer
diameter of the electrode 92 a distance that is equal to twice the
desired gap 99 distance. As previously disclosed, the gap 99
distance is variable between approximately 0.5 mm to 1.5 mm.
[0128] The choke assembly 106 is also manufactured from an
electrically non-conductive material and has a shape that is
consistent with that of the central case portion 95. The choke
assembly 106 is structured and arranged to provide a tight
interference fit at a proximal end of the central case portion 95.
A projection 114 and a ledge portion 115 are structured and
arranged to abut against so as to align the outer peripheral
surface of the electrode 92 properly. The projection 114 is
machined and dimensioned to provide and to maintain the desired gap
99 distance between the inner peripheral surface of the central
case portion 95 and the outer diameter of the electrode 92.
[0129] The choke assembly 106 includes a central portion 109 having
a through hole, i.e., a choke 96. When assembled and ready for
operation, the central portion 109 separates the volume
compensation chamber (VCC) 93 from the choke assembly plenum 116.
The choke 96 provides a fluid connection between the VCC 93 and the
choke assembly plenum 116. The VCC 93 will be described in greater
detail below. During operation of the device 90, the plenum 116 is
fluidly coupled to the downstream portion 117 of the damping
chamber 103 and contains a predetermined volume of ERF. The choke
96 provides a conduit for transmission of the ERF during a stroke
cycle.
[0130] The choke assembly 106 also includes an electrical
connection 112 that is structured and arranged to accommodate a
electrically-conductive metal, e.g., aluminum, spring 100 and to
provide an opening 113 through which an electrical contact (not
shown) can be electrically coupled to a proximal end of the metal
spring 100. The distal end of the metal spring 100 is electrically
coupled to an electrical terminal (not shown) that is disposed on
an end portion of the electrode 92.
[0131] The case end cover 107 is also manufactured from an
electrically non-conductive material and has a shape that is
consistent with that of the choke assembly 106, to which the case
end cover 107 is mechanically coupled, e.g., using a plurality of
machine screws, bolts, and the like. The case end cover 107
includes an electrical connection opening 104 and the VCC 93, in
which a closed-cell foam can be disposed. A distal end 102 of the
case end cover 107 includes a hole 99 for releasably attaching the
case end cover 107 to another object.
[0132] The electrical connection opening 104 in the case end cover
107 is disposed to be in registration with the opening 113 in the
choke assembly 106, for electrically coupling an electrical contact
(not shown) to the proximal end of the metal spring 100.
[0133] The case manifold 105 is also manufactured from an
electrically non-conductive material and has a shape that is
consistent with that of the central case portion 95, to which the
case end cover 107 is mechanically coupled. The case manifold 105
includes an opening 111 that is structured and arranged to
accommodate frictionless translation of the output shaft 94. A
gland 119 is also provided in the case manifold to accommodate a
sealing device 98.
[0134] Optionally, the case manifold 105 further includes a plug
portion 118 that is adapted to accommodate a plug 97 having a
through hole 120 that is structured and arranged to accommodate
frictionless translation of the output shaft 94.
[0135] The piston 91 and output shaft 94 are disposed coaxial to
and within and the damping chamber 103 of the electrode 92. The
piston 91 is precision manufactured to provide clearance between
the outer periphery of the piston 91 and the inner peripheral
surface of the electrode 92 as previously described. The output
shaft 94 is successively disposed through the opening 111 in the
case manifold 105, the sealing device 98, and the through hole 120
in the plug 97. A distal end 101 of the output shaft 94 includes a
hole 99 for releasably attaching the output shaft 94 to another
object.
[0136] Operation of the miniature ERF damping device 90 is
essentially the same as previously described. However, there is
only a single electrode 92 and a single gap 99. The electrode 92 is
a positive (p) pole and is electrically coupled to a voltage source
(not shown) via the metal spring 100 and an external electrical
connection (not shown). The central case portion 95 is made of an
electrically non-conductive material, e.g., Delrin.RTM., and
therefore serves as a ground. Accordingly, when increased
resistivity is desired, the source voltage is delivered to the
electrode 92, which generates an electrical field within the ERF,
causing an increase in yield stress and a corresponding increase in
resistivity.
Diaphragm Seal-Based VRHD
[0137] A diaphragm seal-based VRHD based on rolling seal technology
will now be described. The preferential use of rolling seals
reduces friction because the rolling seals, e.g., rolling seals
manufactured by Dia-Com Corporation of Amherst, N.H., have no
break-free friction, but rather exhibit a constant rolling
resistance throughout a stroke cycle.
[0138] Referring to FIGS. 18-20, the embodied VRHD 150 includes a
handle portion 20, a damping system 155, and at least one sensing
device, e.g., a load cell 12.
[0139] The moving handle portion 21 of the handle portion 20 is
mechanically coupled to the first ends of a pair of elongate
members 151. The second, opposite ends of the elongate members 151
are mechanically coupled to a bracket 153 to which the load cell 12
sensing device is releasably attached.
[0140] The load cell 12 is mechanically coupled to the output shaft
158 of the damping system 155, which is mechanically coupled to a
first damping piston 152. The first damping piston 152 is
structured and arranged to translate along the longitudinal axis of
a first, damping chamber 157. More specifically, the first damping
piston 152 and rolling diaphragm seal 156 are adapted, during a
gripping load, to force an ERF through the gaps 165 of an ERF valve
160 into a second chamber 159. During a release period, a second,
spring-biased piston 156 is adapted to force the ERF back through
the gaps 165 in the ERF valve 160 into the first, damping chamber
157. The ease with which the damping piston 152 forces the ERF
through the ERF valve 160 is selectively variable, by applying a
voltage to a plurality of positive polarity members 162 within the
ERF valve 160, while maintaining negative polarity members 164
adjacent to the positive polarity members 162 at ground.
[0141] As previously described, voltage applied to the positive
polarity members 162 generates an electric field within the ERF
that is disposed within the gaps 165 between adjacent positive and
negative polarity members 162, 164. The yield stress of the
activated ERF increases, making it more difficult to force the ERF
through the ERF valve 162. Because the magnitude of the voltage and
the duration of its application to the positive polarity members
162 are controllable, the resistivity of the VRHD 90 is
tunable.
[0142] A rolling diaphragm seal 156 is disposed at a distal end of
the first piston 152. As shown in FIG. 21, the diaphragm seal 156
isolates the piston 156 from the ERF fluid that fills the first
chamber 157. The peripheral edge 160 of the diaphragm seal 156 is
releasably attached to or between the inner wall of the first
chamber 157. When the first piston 152 is in a no-load, at-rest,
retracted position, the excess diaphragm material is preserved as a
diaphragm loop 164 that is disposed in the gap 162 between the
first piston 152 and the inner diameter of the first damping
chamber 160.
[0143] As the first, damping piston 152 is forced towards the
distal end of the first chamber 157, the loop 164 decreases in size
until it is displaced to the point of its greatest reach. When
fully extended to the point of its greatest reach, the diaphragm
seal 156 should not be stretched excessively beyond its elastic
yield stress.
[0144] A second, spring-biased piston 154 is disposed in a second
chamber 159, opposite the first piston 152. ERF forced through the
ERF valve 160 by the action of the damping piston 152 and diaphragm
156 compresses the spring portion of the spring-biased piston 154,
causing it to displace commensurate with the volume of ERF that is
forced from the first chamber 157 to the second chamber 159. Once
the patient/user releases his or her grip, the spring-biased piston
154 forces the ERF from the second chamber 159 back through the ERF
valve 160, and back into the first, damping chamber 157. The ERF
entering the damping chamber 157 exerts a force against the
diaphragm 156 and the damping piston 152, returning each to their
no-load, at-rest position.
[0145] During operation, as described above, as a patient/user
applies a force to a moving handle portion 21, the load is
transferred to the output shaft 158, causing the damping piston 152
and diaphragm seal 156 to force ERF through the ERF valve 160 into
the second chamber 159. The ease with which the ERF passed from the
first damping chamber 157 into the second chamber 159 can be
controlled selectively by applying a voltage to positive polarity
members in the ERF valve 160
[0146] As the ERF fluid passes into the second chamber 159, the
force of the ERF exceeds the spring constant of the spring member
(not shown) that biases the second piston 154, causing the second
piston to displace, e.g., elastically, within the second chamber
159. When the patient/user ceases gripping the handle portion 21,
the spring constant of the spring member biases the second piston
154 towards the ERF valve 160, forcing the ERF fluid back into the
first, damping chamber 157 and further forcing the first, damping
piston 152 and the diaphragm 156 back to their no-load, at-rest
positions.
Portable, Rotary ERF Damping System
[0147] Referring to FIG. 22 and FIG. 23, embodiments of a portable,
rotary ERF brake 130 using plural electrodes 125 and the ERF-based
damping technology described herein, respectively, are shown. For
this particular application, a rotary-type device 130 is preferred
to a linear device because it can be made more compact and because
of the open-loop performance advantage that rotary ERF devices
inherently have over linear ERF devices. Indeed, rotary ERF devices
operate more smoothly and lend themselves to a more user friendly
demonstration because they can be handheld and do not require
additional frame support or associated linear motion guides.
[0148] The brake body 121, which includes a first, upper portion
121a and a second, lower portion 121b, of the device 120 are,
preferably, fabricated from an electrically non-conductive
material, e.g., Delrin.RTM.. The upper portion 121a of the brake
body 121 is structured and arranged to accommodate a first
plurality of rotatable electrodes 125a and the lower portion 121b
of the brake body is structured and arranged to accommodate a
second plurality of stationary electrodes 125b.
[0149] Each electrode of the plurality electrodes 125 is
manufactured as a hollow or substantially hollow cylinder out of an
electrically conductive metal, such as aluminum. Each of the first
plurality of rotatable electrodes 125a and is structured and
arranged to be mutually concentric and coaxial and each of the
second plurality of stationary electrodes 125b is structured and
arranged to be mutually concentric and coaxial. The first plurality
of rotatable electrodes 125a includes a center hub 138 that is
connected to each of the plurality of stationary electrodes 125a
via a circular or substantially circular bottom plate 126. The
second plurality of stationary electrodes 125b does not have a hub,
however, each of the plurality of electrodes 125b is connected to
every other of the plurality of stationary electrodes 125b via an
annular circular bottom plate (not shown).
[0150] Preferably, the second plurality of electrodes 125b is
stationary and has a positive (p) polarity and the first plurality
of electrodes 125a is rotatable and has a negative (n) polarity, or
ground. The gap distance 129 between each of the first plurality of
electrodes 125a and the gap distance 129 between the second
plurality of electrodes 125b are both equal to twice the desired
gap distance between adjacent electrodes of opposite polarity.
Those of ordinary skill in the art can appreciate, however, that
the gap distances can be selectively chosen, which is to say, they
can differ. The heights, or engagement lengths, of the electrodes,
whether positive polarity or negative polarity also can be varied
to provide additional tuning.
[0151] A safe high voltage (SHV) connector(s) 123 and a power
cable, e.g., an RG58 coaxial cable (not shown), are provided in the
lower portion 121b of the body, to electrically couple the
rotatable electrodes 125a to the power source (not shown) and/or to
a control box (not shown). To make the device 130 portable a custom
battery-powered control box can be used.
[0152] To deliver power from the SHV connector(s) 123, which is
disposed in the lower portion 121b of the body, to the rotatable
electrodes 125a, which are disposed in the upper portion 121a of
the body, a rotatable, threaded, elongate body, e.g., a rod 122, is
electrically coupled to the first plurality of electrodes 125a and
to the SHV connector(s) 123. The rod 122 is structured and arranged
to operate frictionlessly within the central opening 138 of the hub
127.
[0153] An electrically non-conductive metal, e.g., brass, plain
bearing(s) 124 is used for supporting and centering the rotating
rod 122. The bearing(s) 124 and a conductive grease provides a
stable, low-noise electrical pathway. An output shaft 135, e.g., a
stainless steel shaft, is provided and mechanically coupled to a
hand crank 133 at a first end and to the rotating rod 122 at a
second end.
[0154] When assembled, the body is air- and water-tight so as to
provide a suitable reservoir 137 for the ERF. When the reservoir
137 is filled, the ERF invades the gaps 129 between the electrodes
125a and 125b. Slide valves 128 are provided in the lower portion
121b of the body and fluidly coupled to the reservoir 137, for
draining, bleeding, and filling the reservoir 137 of the rotary
device 120.
[0155] Operation and control of the portable, rotary ERF brake 130
is similar to that previously described above. A controller (not
shown) for the device 130 slows, retards, or arrests rotation of
the shaft 135 and the rod 124 as a function of the magnitude of the
applied low-amperage current and the duration of the application of
the current to the positive polarity electrodes 125b. More
specifically, when current is delivered to the stationary
electrodes 125b, an electrical filed is generated between adjacent
electrodes 125a and 125b, which affects the yield stress of the
ERF, making further rotation of the rotatable electrode 125a more
difficult.
[0156] Many changes in the details, materials, and arrangement of
parts and steps, herein described and illustrated, can be made by
those skilled in the art in light of teachings contained
hereinabove. Accordingly, it will be understood that the following
claims are not to be limited to the embodiments disclosed herein
and can include practices other than those specifically described,
and are to be interpreted as broadly as allowed under the law.
* * * * *