Continuous passive motion device for a wrist

A therapeutic passive motion device for rehabilitating a wrist includes a main housing unit which encloses a reciprocating motion producing device. A yoke member extends outwardly from the main housing unit. A first, generally V-shaped, link mechanism is pivotally connected to an end of the yoke and carries a hand-supporting member. A second link mechanism is pivotally connected to an output member of the motion producing device and to the first link mechanism. An electric motor is advantageously employed to drive the motion producing device, whereby the hand-supporting member is caused to pivot in an oscillating fashion relative to the yoke member and the main housing unit.

FIELD OF THE INVENTION 
The present invention relates to devices which effect continuous passive 
motion of a limb or joint. More particularly, the present invention 
relates to portable devices which produce continuous and/or cyclic 
movements in a human wrist while the wrist remains in a passive state. 
BACKGROUND OF THE INVENTION 
In the field of post-trauma and post-operative physical therapy for the 
rehabilitation of joints, it is generally known that the occurrences of 
capsular, ligamentous and articular adhesions, thromboembolisms, venous 
status, post-traumatic osteopenia, peripheral edema, muscle atrophy and 
the like can be reduced by an early mobilization of the injured or 
surgically treated joint with a continuous passive motion device (CPM). 
Various continuous passive motion devices have been proposed for effecting 
post-trauma or post-operative movements of an injured or surgically 
treated limb or joint. These devices are often driven by an electric motor 
and operate to continuously and repeatedly flex the affected or associated 
joint at a predetermined speed and through a predetermined range of 
motion. Moreover, these devices may be specially adapted for use in 
conjunction with a particular joint, such as a knee, elbow or wrist. An 
example of a motor driven CPM that is specially adapted for use e.g. in 
the rehabilitation of a knee or hip joint is disclosed in U.S. patent 
application Ser. No. 07/760,291, entitled "Continuous Passive Motion 
Device for a Limb" assigned to the assignee of the present invention and 
incorporated by reference herein. 
In designing a portable continuous passive motion device, the size and/or 
the power output capacity of the motor is chosen in dependence not only on 
an actual anticipated load which the device is likely to encounter during 
operation (such as the weight or the resistance to movement of a leg, arm 
or hand), but also on the effective "gearing ratio" (or mechanical 
advantage) which exists between the motor and the limb or joint moving 
member of the CPM. This effective gearing ratio is a function of the 
particular motion conversion mechanism which is utilized in the CPM to 
change the (e.g. rotary) output motion of the motor into the (e.g. 
oscillatory or reciprocating) output motion of the limb or joint moving 
member. Moreover, depending on the particular motion conversion mechanism 
which is utilized, the effective gearing ratio between the motor and the 
limb or joint moving member may vary e.g. over the range of movement of 
the limb or joint moving member. 
A continuous passive motion device for a wrist is known, for example, from 
U.S. Pat. No. 5,067,479. This device employs an eccentric transmission for 
driving a pivoting slide to convert a rotary motion of an electric motor 
into a pivoting motion of a wrist-supporting tubular shaft driven by the 
slide. As will become apparent to those skilled in the art, the effective 
gearing ratio (or mechanical advantage) of such a motion conversion 
mechanism ranges from a minimum when an axis of the pivoting slide is 
parallel to an effective working radius of the eccentric transmission 
(e.g. when the wrist is in an unflexed position) to a near infinite 
maximum when the axis of the pivoting slide is disposed tangentially to 
and parallel with the plane of an effective circumference defined by the 
effective working radius of the rotating eccentric transmission. Due to 
the relatively large variance in the effective gearing ratio of such a 
motion conversion mechanism, the selection of a proper size and/or power 
output capacity for the electric motor is necessarily controlled by 
countervailing functional and practical design constraints. Specifically, 
if a relatively large size and/or power output capacity for the electric 
motor is chosen so as to accommodate the actual anticipated load when the 
effective gearing ratio is at the minimum, then that motor exhibits a 
substantial overcapacity in power output when the wrist-supporting tubular 
shaft is at a position where the minimum effective gearing ratio does not 
exist. Conversely, if a relatively small size and/or power output capacity 
for the electric motor is chosen so as to reduce an overcapacity condition 
in the power output of the motor when the effective gearing ratio is not 
at a minimum, then the power output capacity of that motor may be 
inadequate to overcome the actual anticipated load when the 
wrist-supporting tubular shaft is at a position where the minimum 
effective gearing ratio exists in the motion conversion device. 
While a relatively large motor functions adequately even when the minimum 
effective gearing ratio exists in the motion conversion device of the CPM, 
several practical design constraints weigh against the selection of such a 
motor. Specifically, both the cost and the aesthetic appearance of the CPM 
are adversely affected by the selection of a relatively large motor. Also, 
fin order to accommodate the larger reaction forces generated by the 
relatively large motor, the design of the CPM housing necessarily becomes 
more complex. Additionally, a relatively large motor consumes more 
electric power than a relatively small motor. 
Accordingly, it will become apparent that the selection of the proper size 
and/or power output capacity of an electric motor for a portable wrist CPM 
with an eccentric transmission-type motion conversion mechanism involves a 
balancing of, or alternately, a compromise between, functional and 
practical design constraints. 
SUMMARY OF THE INVENTION 
Briefly stated, the present invention is directed toward a therapeutic 
passive motion device for effecting wrist movement in a user. The device 
includes a main housing unit and a yoke member rigidly supported by and 
extending outwardly from the main housing unit. A first link mechanism is 
pivotally connected to an end of the yoke member remote from the main 
housing unit at a first pivotal connection, and a hand-supporting assembly 
is mounted on the first link mechanism. In use, the main housing unit is 
adapted to be secured to the forearm of the user in such a manner that the 
associated wrist of the user is in general alignment with the first 
pivotal connection and the associated hand of the user is supported by the 
hand-supporting assembly. A motion producing device is mounted, for 
example, within the main housing unit and includes an output member which 
undergoes reciprocal movement. A second link mechanism is pivotally 
connected to the first link mechanism at a second pivotal connection and 
to the output member of the motion producing device at a third pivotal 
connection. According to the invention, the second link mechanism 
transforms the reciprocal movement of the output member of the motion 
producing device into an oscillatory movement of the first link mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Certain terminology is used in the following description for convenience 
only and is not limiting. For example, the words "right", "left", "lower" 
and "upper" designate directions in the drawings to which reference is 
made. The words "above" and "below" refer to relative positions in the 
drawings to which reference is made. The words "inwardly" and "outwardly" 
refer to directions toward and away from the geometric center of the wrist 
CPM or designated parts thereof. The certain terminology will thus include 
the words above specifically mentioned, derivatives thereof, and words of 
similar import. 
Referring now to the drawings in detail, wherein like numerals indicate 
like elements throughout, there is shown in FIGS. 1 to 11 a preferred 
embodiment of a continuous passive motion device (CPM) for a wrist, 
indicated generally at 20. The wrist CPM 20 includes a main housing unit 
22 (made from plastic or other suitable lightweight, high strength 
materials) having an upper portion 24 and a lower portion 26 which 
cooperate in a clamshell-type manner to form an enclosure for a motion 
producing device and other associated internal components of the CPM, as 
will be more fully described below. A yoke member 28, which includes two 
spaced-apart arms 30, is rigidly supported by and extends outwardly from 
the upper portion 24 of the main housing unit 22. In the preferred 
embodiment, the yoke member 28 is formed integrally with the upper portion 
24 of the main housing unit 22 from the same material. However, the yoke 
member 28 may also constitute a separate article, which may be formed of a 
different material, which is attached to the main housing unit 22. A 
plurality of stiffening ribs 32 are preferably integrally provided on each 
of the arms 30 and in the area between each of the arms 30 and the upper 
portion 24 of the main housing unit 22 to provide enhanced structural 
support and strength to the arms 30. 
At the outward (i.e. remote from the main housing unit 22) ends of the two 
spaced-apart arms 30, generally coaxially arranged first pivotal 
connection parts 34 (which together comprise a first pivotal connection) 
are provided to pivotally connect the outer ends of each of the 
spaced-apart arms 30 to a first link mechanism 36. As shown in FIG. 5, the 
first pivotal connection parts 34, in the present embodiment, 
advantageously take the form of ball joints which accommodate a small 
amount of relative angular movement between the yoke 28 and the first link 
mechanism 36 about axes perpendicular to the pivot axis of the first 
pivotal connection parts 34. Other types of pivotal connecting components 
may alternatively be employed. 
As shown most clearly in FIGS. 1 and 4, the first link mechanism 36 (also 
made from plastic or other lightweight, high strength suitable material) 
is generally V-shaped when viewed from the side or when viewed in 
longitudinal cross-section. The first link mechanism 36 comprises a first 
bifurcated leg portion 38 and a second bifurcated leg portion 40 which are 
joined to one another (e.g. so as to form an acute angle therebetween) in 
the vicinity of an apex or apex portion 42. As such, in the preferred 
embodiment, the first link mechanism is a rigid, unitary 
torque/force-transmitting member. The term "link mechanism" as used herein 
encompasses both a unitary torque/force-transmitting member made from a 
single piece and a torque/force-transmitting arrangement made from a 
plurality of pieces which function in unison. 
The first bifurcated leg portion 38 terminates in a pair of free ends 44 at 
a position remote from the apex portion 42. These free ends 44, which 
together constitute an end portion of the first bifurcated leg portion 38, 
are connected to an end of the yoke member 28 (constituted by the outer 
ends of the spaced-apart arms 30) remote from the main housing unit 22 at 
the first pivotal connection. A hand-supporting assembly 46 is mounted on 
the first link mechanism 36 at a position near the apex portion 42 in a 
manner which will be hereinafter more fully described. 
As will become apparent to those skilled in the art, the main housing unit 
22, the yoke member 28, the first pivotal connection parts 34, and the 
hand-supporting assembly 46 are arranged in such a manner that when the 
main housing unit 22 is properly secured to a forearm of a user, the 
carpal joint of the user's wrist is in general alignment with the first 
pivotal connection and the user's hand is (e.g., substantially 
horizontally) supported by the hand-supporting assembly 46, as described 
below. For the purpose of properly securing the forearm of the user to the 
main housing unit 22, the upper portion 24 of the main housing unit is 
provided with a plurality of longitudinally arranged securing elements 48 
(which may take the form of selectively removable rods). In the preferred 
embodiment, the forearm of the user is secured to a forearm splint 48a 
(only a portion of which is shown in FIG. 6) which includes two sets of 
two parallel channels 48b (see FIGS. 1 and 6) each for slidably receiving 
a securing element 48. Alternatively, straps or attaching portions of soft 
goods (not shown in FIG. 1) can be adapted to be fed beneath the securing 
elements 48 and wrapped around the user's forearm, whereby the user's 
forearm may be secured to the top portion 24 of the main housing unit 22 
without the need for the splint 48a. While the user's hand can merely rest 
on the hand-supporting assembly 46, it is preferred that a strap (not 
shown) be used to secure the user's hand to the hand-supporting assembly. 
A motion producing device, indicated generally at 50 in FIG. 4, is enclosed 
within the main housing unit 22. The motion producing device 50 includes a 
reversible electric motor 52 having a rotary output or output shaft 
(unnumbered) which drives a ball screw and nut mechanism 54 through a gear 
transmission 56. The ball screw and nut mechanism 54 has a constant 
gearing ratio throughout its range of operation and functions as a motion 
conversion device for converting the reversing rotary driving motion of 
the electric motor output shaft into reciprocating motion. 
As shown in particular in FIG. 8, the gear transmission 56 is, in the 
preferred embodiment, a reduction gear transmission which comprises a 
drive gear 58 attached to the output shaft of the motor 52 that engages a 
driven gear 60. The driven gear 60 is drivingly connected to a linear 
screw 62 (FIG. 4) of the ball screw and nut mechanism 54. The linear screw 
62 is journalled for rotation within the main housing unit 22 between the 
upper and lower portions 24, 26. A non-rotatable nut or nut assembly 64 is 
carried by the linear screw 62 and driven in a reciprocating fashion by 
the reversing rotation of the linear screw 62. The nut assembly 64 
constitutes the linear output member of the motion producing device 50. 
Details of the nut assembly 64 are shown in FIGS. 4 and 6. Specifically, 
the nut assembly 64 includes upstanding guide projections 66 which are 
received within a longitudinally extending interior guide channel 68 
formed in the upper portion 24 of the main housing unit 22. The guide 
projections 66 and guide channel 68 cooperate to prevent rotation of the 
nut assembly 64. Vertically between the nut assembly 64 and the upper 
portion 24 of the main housing unit 22, a sensing assembly (in the form of 
a linear potentiometer) is provided for sensing the linear position of the 
nut assembly along the linear screw. In particular, a conductive wiper 70 
of the linear potentiometer is fixed to a top portion of the nut assembly 
64. Above the wiper, an electrically conductive resistance strip 72 
(having a known electrical resistance per unit of length), and a parallel 
conductive path are fixed to the upper portion 24 of the main housing unit 
22. As the nut assembly reciprocates along the linear screw 62, the 
conductive wiper 70 slides along both the resistance strip 72 and the 
parallel conductive path. A sensed electrical resistance ratio between the 
parallel conductive path and each end of the resistance strip 72 provides 
an indication of the linear position of the nut assembly 64 along the 
linear screw 62 for control purposes which will hereinafter be described. 
Lastly, as shown in FIG. 6, a pair of horizontally disposed and laterally 
opposed pivot pins 74 extend outwardly from the nut assembly 64. 
It is noted that, in the preferred embodiment, conventional antifriction 
elements are employed in the nut assembly 64 to reduce the amount of 
friction generated between the linear screw 62 and the nut assembly 64. 
These antifriction elements may take the form of recirculating or 
non-recirculating ball bearings (not shown) which are provided at the 
mechanical interface between the linear screw 62 and the nut assembly 64. 
Other types of antifriction elements may alternatively be employed. 
The output member of the motion producing device 50 drives the first link 
mechanism 36 to pivot about the pivotal connection 34 by means of a second 
link mechanism 76. Specifically, as shown in FIGS. 4 to 6, a pair of 
curved links 78 (which together constitute the second link mechanism 76) 
include a pair of first ends 80 (which together constitute a first end 
portion of the second link mechanism 76) and a pair of second ends 86 
(which together constitute a second end portion of the second link 
mechanism 76). Free ends 82 of the second bifurcated leg portion 40 (which 
together constitute an end portion of the second bifurcated leg portion 
40) of the first link mechanism 36 are pivotally connected to the first 
ends 80 of the curved links 78 by means of a pair of second pivotal 
connection parts 84 (which together constitute a second pivotal 
connection). The curved links 78 are pivotally connected at their second 
ends 86, by means of a third pivotal connection, to the output member of 
the motion producing device 50 i.e through the intermediary of the opposed 
pivot pins 74 which extend outwardly from the nut assembly 64. 
Accordingly, during operation of the CPM, the second link mechanism 76 
functions as a force-transmitting member between the output member (i.e. 
the nut assembly 64) of the motion producing device 50 and the second 
bifurcated leg portion 40 of the first link mechanism 36 to transform the 
reciprocating movement of the nut assembly 64 into an oscillatory movement 
of the first link mechanism 36 about the pivot axis defined by the first 
pivotal connection parts 34. Moreover, it becomes apparent that the first 
and second link mechanisms 36, 76 and the yoke member 28 attached to the 
main housing unit 22 together cooperate to form an offset slider-crank 
motion conversion device for transforming the reciprocating movement of 
the output member 64 of the motion producing device 50 into an oscillatory 
pivoting movement of the hand-supporting assembly 46. 
FIGS. 1, 2 and 4 reveal the details of the preferred embodiment of the 
hand-supporting assembly 46 shown in FIG. 1. Specifically, as shown in 
FIG. 4, the hand-supporting assembly comprises a hand-supporting member 88 
preferably made of a resilient material such as a rubber pad or the like 
secured to a base plate assembly 98 which is mounted on a supporting plate 
90 by means of an arcuate slide assembly, indicated generally as 92. The 
hand-supporting member 88 is preferably releasably secured to the base 
plate 98 with hook-and-loop material 88a. The supporting plate 90, in 
turn, is mounted on the first link mechanism 36 at a position near the 
apex portion 42 thereof by means of a linear slide assembly, indicated 
generally as 94. As shown e.g. in FIG. 3, a line of movement of the 
arcuate slide assembly 92 extends generally transversely to a line of 
movement of the linear slide assembly 94. 
Referring now to FIGS. 4 and 9-11, the arcuate slide assembly 92 provides 
for limited arcuate movement of the hand-supporting member 88 relative to 
the supporting plate 90. The base plate 98 includes upper and lower 
portions 98a, 98b adhesively secured together in a standard manner well 
understood by those skilled in the art. A cavity 98c is formed between the 
upper and lower portions 98a, 98b. The lower portion 98b includes an 
arcuate slot 100 (see FIG. 2). A slide member 96 is received within the 
arcuate slot 100 formed within the lower portion 98b of the base plate 98. 
The slide member 96 includes a pair of retaining flanges 114 positioned 
within the cavity 98c for retaining the slide member 96 within the slot 
100 and to permit the slide member 96 to slide or move with respect to the 
slot 100 and hand-supporting member 88. A pair of radially extending 
locking pins 106 are formed in the opposite or distal end 96a of the 
sliding member 96 from the retaining flanges 114. Positioned between the 
retaining flanges 114 and the locking pins 106 is an intermediate section 
96b which is generally square in cross section (see FIG. 10). 
Referring now to FIGS. 4 and 11, the intermediate section 96b and locking 
pins 106 are positioned through a correspondingly sized aperture 90a in 
the supporting plate 90. The aperture 90a is sized to receive the 
intermediate section 96b therein to prevent the sliding member 96 from 
rotating with respect to the supporting plate 90. The sliding member 96 is 
maintained within the aperture 90a and secured to the supporting plate 90 
by a lock knob 112, as described in more detail hereinafter. Thus, the 
hand-supporting member 88 and base plate 98 are movable with respect to 
the supporting plate 90 along a curved path defined by the arcuate slot 
100. 
The positioning and the degree of curvature of the arcuate slot 100 is 
chosen to generally or substantially duplicate the arc of possible lateral 
(or side-to-side) movement which a human hand may undergo when an 
associated carpal joint of the wrist is positioned to be in general 
alignment with the axis of the first pivotal connection parts 34. It will 
thus be apparent to those skilled in the art that the arcuate slide 
assembly 92 constitutes a mechanism by which the lateral position of the 
hand-supporting member 88 may be adjusted to accommodate and tailor the 
wrist CPM 20 to the specific needs of individual wrist CPM users. 
A locking assembly, indicated generally at 102 in FIG. 3, is provided to 
selectively lock a lateral position of the hand-supporting member 88 
relative to the supporting plate 90. The locking assembly 102 includes the 
lock knob 112 which includes an aperture 112a for complementarily 
receiving the distal end 96b of the sliding member 96. That is, the 
locking pins 106 and generally cylindrical distal end 96a are positioned 
through the aperture 112a until the locking pins 106 clear the aperture 
112a. As such, the lock knob 112 is rotatable with respect to the sliding 
member 96. As best shown in FIG. 3, the lock knob 112 includes first and 
second sets 108a, 108b of cam formations and a pair of stop elements 110 
which protrude upwardly from the lock knob 112. The lock knob 112, locking 
pins 106 and aperture 90a cooperate to fasten the base plate 98 to the 
supporting plate 90, as described in more detail below. 
Operation of the locking assembly 102 is as follows. The base plate 98 is 
positioned with respect to the supporting plate 90 such that the distal 
end 96a of the sliding member 96 is positioned through the aperture 90a in 
the supporting plate 90. In this position, the sliding member 96 is 
rotatably fixed with respect to the supporting plate 90. The lock knob 112 
is then positioned to receive the distal end 96b of the sliding member 96 
and the locking pins 106 through the aperture 112a of the lock knob 112. 
That is, the locking pins 106 are positioned through the aperture 112a 
until they are positioned on the opposite side of the lock knob 112 from 
the supporting plate 90. In this first angular position, the base plate 98 
and sliding member 96 are easily removable from the supporting plate 90. 
The lock knob 112 is then rotated clockwise (as viewed in FIG. 3) 
approximately 45.degree. until the locking pins 106 are positioned between 
the first and second sets of cam formations 108a, 108b. In this position, 
the base plate 98 cannot be removed from the supporting plate 90, but is 
permitted to move or slide with respect to the supporting plate 90 due to 
the sliding connection between the sliding member 96 and the arcuate slot 
100. Further rotation of the lock knob 112 clockwise approximately 
45.degree. causes the locking pins 106 to ride over the second set of cam 
formations 108b. The second set of cam formations 108b have a greater 
height than the first set of cam formations 108a to cause the supporting 
plate 90 and base plate 88 to be compressed together. In this position, 
the compressive forces are sufficient to lock the base plate 98 to the 
supporting plate 90 and prevent sliding movement between the sliding 
member 96 and arcuate slot 100. By moving the lock knob 112 through the 
three different positions, the hand-supporting member 88 can be either 
removed from the supporting plate 90, be permitted to move in an arcuate 
manner with respect to the supporting plate 90, or be fixed to the 
supporting plate 90. 
The linear slide assembly 94 provides for limited sliding movement of the 
hand-supporting assembly 46 relative to the first link mechanism 36 in 
directions substantially towards and away from the first pivotal 
connection. As shown in FIG. 3, the linear slide assembly comprises a pair 
of slide pins 118 which are fixed to distal flanges 120 of the supporting 
plate 90. Each of the slide pins 118 are further supported by a flange 122 
which extends downwardly from the supporting plate 90. 
Each of the slide pins 118 is slidably received within guide bushings (only 
one of which is shown at 124 in FIG. 1) selectively provided within a 
plurality of guideway openings 126 (FIG. 3) that are strategically 
provided e.g. in the vicinity of the apex portion 42 of the first link 
mechanism 36. Accordingly, since the slide pins 118 are slidable (against 
minimal friction force created by the bushings 124) relative to the first 
link mechanism 36, the hand-supporting assembly 46 is free to slide as the 
first link mechanism 36 undergoes its angular excursion shown in FIG. 4. 
The wrist CPM 20 according to the present invention is adapted for use with 
a remote CPM controller e.g. of the kind described in U.S. patent 
application Ser. No. 07/760,424 entitled "Controller for Continuous 
Passive Motion Devices", assigned to the assignee of the present invention 
and incorporated by reference herein. As shown in FIGS. 4 and 7, the main 
housing unit 22 of the wrist CPM 20 includes, suitably supported at a rear 
portion thereof, interface components including an electrical connector 
128 and a user-operated momentary switch 130. The electrical connector 128 
is adapted to be connected, via a suitable (e.g. six conductor) signal 
cable/connector assembly (not shown), to the remote CPM controller (also 
not shown). The CPM controller receives a signal from the linear 
potentiometer described above which is indicative of the longitudinal 
position of the nut assembly 64 on the linear screw 62 and a (e.g. back 
EMF) signal from the motor 52 which is indicative of the speed and load 
under which the motor 52 is operating. In accordance with these and other 
inputs described in the aforementioned patent application, the CPM 
controller provides signals to the electric motor 52 to control the speed, 
direction and torque of the motor as well as the force or load under which 
automatic motor reversal is effected. 
The geometrical relationships (e.g. the relative sizes, shapes, and 
positions) which exist between the main housing unit 22, the yoke member 
28, the first link mechanism 36, the second link mechanism 76 and the 
motion producing device 50 are chosen to minimize (e.g. in light of 
practical considerations), or at least reduce, the degree of variance 
which occurs in the effective "gearing ratio" of the linkage-type motion 
conversion mechanism that converts the reciprocating movement of the 
output member of the motor 52 into the oscillatory movement of the 
hand-supporting assembly 46 over the operative range of movement of the 
linkage-type motion conversion mechanism. The term "gearing ratio" as 
employed herein does not imply that gears are utilized in the linkage-type 
motion conversion device. It merely refers to the multiplication or 
division of a magnitude of a driving force, or alternately, to the 
division or multiplication of the amount of movement produced by the 
driving force, which occurs when the driving force is transmitted through 
the motion conversion mechanism. Such a minimization of or reduction in 
the degree of variance in the effective gearing ratio of the linkage-type 
motion conversion device simplifies the electric motor selection in the 
CPM design process in that it enables a more appropriately sized (e.g. 
smaller) motor to be effectively employed in the wrist CPM 20. 
Specifically, the geometrical relationships between the motion producing 
device 50, the first and second link mechanisms 36, 76, the yoke member 28 
and the main housing unit 22 are such that: 
a) during driving movement of the driving motor output shaft, a ratio 
(d.psi./dx) is established between a rate of change of angular movement of 
the first link mechanism 36 and a rate of change of linear movement of the 
output member of the motion producing device 50 for each position of the 
output member over an entire operative range of positions through which 
the output member is adapted to travel according to the relationship: 
##EQU1## 
wherein .psi.=the angular position of the first link mechanism 36 with 
respect to the axis of the first pivotal connection; 
a=the distance from an axis of the first pivotal connection to a reference 
point on a reference line, wherein the reference line is defined by a 
direction of movement of the output member of the motion producing device 
50, and wherein the reference point is established such that a line from 
the axis of the first pivotal connection to the reference point is 
orthogonal to the reference line; 
x=the distance (e.g. either positive or negative) between the reference 
point and an axis of the third pivotal connection; 
m.sup.2 =a.sup.2 +x.sup.2 ; and 
c.sup.2 =L.sup.2 -R.sup.2 -a.sup.2, 
wherein L is the distance between the third pivotal connection and the 
second pivotal connection; and 
R is the distance between the first pivotal connection and the second 
pivotal connection; and 
(b) during driving movement of the drive motor output shaft, and over the 
entire operative range of positions through which the output member is 
adapted to travel, a maximum value of the ratio between the rate of change 
of angular movement of the first link mechanism 36 and the rate of change 
of linear movement of the output member of the motion producing device 50 
is no greater than twice a minimum value of the ratio between the rate of 
change of angular movement of the first link mechanism 36 and the rate of 
change of linear movement of the output member of the motion producing 
device 50. In other words, the geometrical relationships between the yoke 
member 28 supported by the main housing unit 22, the first and second link 
mechanisms 36, 76, and the motion producing device 50 are such that during 
reciprocating movement of the output member of the motion producing device 
50 and over the entire operative range of positions through which the 
output member is adapted to travel, a maximum value of an effective 
gearing ratio between the output member of the motion producing device 50 
and the first link mechanism 36 is no greater than twice a minimum value 
of the effective gearing ratio between the output member of the motion 
producing device 50 and the first link mechanism 36. 
FIGS. 12 to 14 reveal other hand-supporting members which may be attached 
to the supporting plate 90 of the wrist CPM 20 of FIGS. 1 to 11. 
Referring to FIG. 12, there is shown a generally vertically extending 
padded hand-supporting member 132 which includes a base plate portion 134 
and a generally vertically extending frame portion 136 integral therewith. 
A pad member 138 encircles the frame portion 136. A lock knob 112' is 
provided to removably attach the base plate portion 134 to the supporting 
plate 90. The hand-supporting member 132 is attached to the supporting 
plate 90 in a manner generally identical to that described above in 
connection with attaching the base plate 98 to the supporting plate 90, 
except that arcuate sliding movement is not possible, since the 
hand-supporting member 132 does not include an arcuate slot. Hence, the 
hand-supporting member 132 is locked to the supporting plate 90 when the 
locking pins 106' are positioned over the second set of cam formations 
108b'. The hand-supporting member 132 is employed in the wrist CPM 20 when 
it is desired to flex the wrist while the hand is disposed in a 
substantially vertical orientation (as opposed to a substantially 
horizontal orientation for the embodiment of FIGS. 1-11). The pad member 
138 is trimmable with scissors or other cutting devices to accommodate 
different hand widths. A screw-down padded flange 138a and the base slate 
portion 134 keep the user's hand positioned on the pad member 138 between 
the screw-down padded flange 138a and the base plate portion 134. 
Referring now to FIGS. 13 and 14, there is shown a substantially 
horizontally disposed hand-supporting member 140 (made from plastic or 
other suitable material) around which a user's fingers are adapted to 
curl. A resilient pad 141 covers the hand-supporting member 140 which is 
mounted on the supporting plate 90 by means of an assembly identical to 
that described above in connection with FIGS. 1-11 which includes an 
arcuate slide assembly 92'', stop elements 110'', a lock knob 112'', and 
retaining flanges 114''. The hand-supporting member 140 comprises first 
and second interfitted portions 142, 144 which are adapted to be snap-fit 
together, capturing the sliding member 96'' between the first interfitted 
portion 142 and an apertured flange 146 of the second interfitted portion 
144. 
From the foregoing description, it can be seen that the present invention 
comprises a wrist CPM having a linkage-type motion conversion assembly for 
efficiently converting a reciprocating motion of an output member of a 
motion producing device into an oscillatory pivoting motion of a 
hand-supporting member. It will be appreciated by those skilled in the art 
that changes and modifications may be made to the above described 
embodiment(s) without departing from the inventive concept thereof. It is 
understood, therefore, that the present invention is not limited to the 
particular embodiment(s) disclosed, but is intended to include all 
modifications and changes which are within the scope and spirit of the 
invention as defined by the appended claims.