Physical therapy apparatus and method

A physical therapy apparatus and method are provided for increasing the range of motion of joints, such as knee and elbow joints, that have lost their normal range of mobility. The apparatus includes support means for positioning and supporting the upper limb of an arm or leg, cradle means for positioning and supporting the lower limb of the same arm or leg which are pivotally connected to the support means so that the resulting axis of rotation coincides with the axis of rotation at the joint between the lower and upper limb positioned thereon, positioning means for selectively setting the position of the cradle means relative to the support means at a desired initial treatment position which does not exceed the allowable pain tolerance of the patient whose joint is being treated, reciprocating means which reciprocate the cradle means from the initial treatmemt position to a variable terminal treatment position to provide continuous uniform passive manipulation of the lower limb so that stretching of the soft tissues in the joint takes place and the range of motion of the joint is gradually increased, variable stroke means to permit the variable terminal treatment position of the cradle means to be controllably varied, and variable power means to operably drive the reciprocating means to provide a predetermined amount of force applied against the cradle means to achieve the desired physical therapy effect at the joint but that can also be resisted and successfully overridden by the patient wherever too much pain or discomfort is experienced.

BACKGROUND 
When a joint, such as a knee or elbow joint, is immobilized while healing 
from an injury, after an operation, or as a result of disease, the soft 
tissues at the joint contract. Motion of the joint is limited both by 
actual physical restraint due to the soft tissues which have contracted 
and by psychological restraint due to the pain that is encountered when 
the soft tissues are stretched. However, to return the joint to its normal 
range of mobility the soft tissues must be stretched to increase the range 
of motion of the joint. 
Stretching of the soft tissues is best carried out by passive manipulation 
of the joint since the muscles that operate the joint are in a weakened 
condition as a result of immobilization. During manipulation of the joint, 
pain will result as scar tissue and adhesions are broken off. The pain 
encountered during passive manipulation of the joint must be controlled 
and always held below the patient's allowable pain tolerance as exceeding 
a patient's pain tolerance can cause new adhesions to be formed and result 
in regression in the condition of the joint. Operation in a comfort zone 
within the patient's allowable pain tolerance is also important since 
stretching of the soft tissues is facilitated as the patient relaxes and 
tense muscles are overcome by weariness. To continually assure operation 
in the comfort zone, the stretching necessarily must be carried out 
gradually over an extended period of time. 
The use of the apparatus of this invention to provide uniform and 
continuous mechanical therapy rather than depending solely upon manual 
therapy is desirable as it is impractical for a physical therapist to 
manually manipulate a joint for an extended period of time for several 
reasons. First, the therapist will not have the stamina to continue the 
treatment in a uniform and consistent manner for an extended period of 
time. However, the apparatus of this invention can provide continuous 
uniform treatment for an extended period. Secondly, the cost of treatment 
that would require a skilled physical therapist's constant attendance and 
total involvement for extended periods of time would be quite expensive. 
On the other hand, the apparatus of this invention can manipulate the 
joint over an extended period of time without the physical therapist being 
in attendance, resulting in lower cost for therapy. Thirdly, a skilled 
physical therapist must generally rely on a trial and error approach 
through his sense of feel to establish the range of motion of the joint 
that was attained in the previous treatment so as to use it as a starting 
point for the next treatment, to establish a specific desired angle 
through which the joint is reciprocated during treatment, and to establish 
a specific desired amount of force to be applied during the treatment. If 
a physical therapist exceeds the patient's pain tolerance, he may cause 
regression in the condition of the patient or at the very least cause pain 
and discomfort to the patient. However, the apparatus of this invention 
can be controlled so as to accurately and repeatably position the joint 
from one treatment to the next for a desired range of motion. Furthermore, 
the apparatus of this invention additionally permits accurate control of 
the angle through which the joint is reciprocated during passive 
manipulation of the joint and of the amount of force applied during the 
manipulation. 
SUMMARY 
This invention refers to a physical therapy apparatus and method for 
increasing the range of motion in a joint that has reduced mobility. The 
range of motion is increased by gradually stretching the soft parts of the 
joint such as muscles and ligaments by passive manipulation of the joint 
while remaining within the pain tolerance of the patient. 
In one preferred embodiment of this invention, a physical therapy apparatus 
includes support means for positioning and supporting the upper limb of an 
arm or leg, cradle means for positioning and supporting the lower limb of 
the same arm or leg which are pivotally connected to the support means so 
that the resulting axis of rotation coincides with the axis of rotation at 
the joint between the lower and upper limb positioned thereon, positioning 
means for selectively setting the position of the cradle means relative to 
the support means at a desired initial treatment position which does not 
exceed the allowable pain tolerance of the patient whose joint is being 
treated, reciprocating means which reciprocate the cradle means from the 
initial treatment position to a variable terminal treatment position to 
provide continuous uniform passive manipulation of the lower limb so that 
stretching of the soft tissues in the joint takes place and the range of 
motion of the joint is gradually increased, variable stroke means to 
permit the variable terminal treatment position of the cradle means to be 
controllably varied, and variable power means to operably drive the 
reciprocating means to provide a predetermined amount of force applied 
against the cradle means to achieve the desired physical therapy effect at 
the joint but that can also be resisted and successfully overridden by the 
patient whenever too much pain or discomfort is experienced. 
An object of this invention is to provide an apparatus and method for 
passively manipulating a joint of a patient, such as a knee or elbow 
joint, so that therapy in the form of uniform and continuous passive 
manipulation is provided for as long as desired without the continued 
presence of a physical therapist after the variables of the apparatus have 
been initially set. 
A further object is to accurately control the range of motion at which the 
joint is passively manipulated and to precisely control the increments the 
range of motion is increased from one treatment to the next. 
A further object is to permit controlled changes in the angle through which 
the joint is reciprocated and in the force applied during passive 
manipulation of the joint. 
A further object is to permit measurement of the progress of a patient so 
as to allow repeatability in setting the apparatus for a desired range of 
motion, or for a desired angle through which the joint is reciprocated, or 
for a desired force applied so that there is a high degree of consistency 
from one treatment to the next. 
A further object is to provide an apparatus and method for controlling the 
force applied to passively manipulate a joint so that the force applied 
can be resisted and successfully overridden by the patient whenever too 
much pain or discomfort is experienced. 
One further object is to provide an apparatus that is adaptable for either 
mode of motion, i.e. flexion or extension, of a joint operating in a 
single plane. 
Various other objects, advantages, and features of the invention will 
become apparent to those skilled in the art from the detailed description 
of the preferred embodiment taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to the drawings in detail and in particular FIGS. 1-4, there is 
provided a physical therapy apparatus having support means indicated 
generally at A, cradle means indicated generally at B pivotally connected 
to support means A, positioning means indicated generally at C positioning 
cradle means B relative to support means A at an initial treatment 
position, reciprocating means indicated generally at D which reciprocate 
cradle means B from the initial treatment position to a variable terminal 
treatment position, variable stroke means indicated generally at F to 
regulate the stroke of reciprocating means D and thus permit the variable 
terminal treatment position of cradle means B to be controllably varied, 
and variable power means indicated generally at E (best shown in FIG. 4 
and including a system of variable weight means, variable rewind reel 
means, pulley means, and motor means) to operably drive reciprocating 
means D. 
Support means A includes upstanding support means 1, horizontal base 
support 2 secured to upstanding support means 1, winch and rewind reel 
support 3, and diagonal braces 4. Although upstanding support means 1 is 
capable of positioning and supporting the upper limb of an arm or leg at 
the uppermost end of the upstanding support means, preferably the support 
means A will also include upper limb cradle 5 which is rigidly attached to 
upstanding support means 1 by fasteners 6. The upper leg or the upper arm 
of the patient is positioned in upper limb cradle 5 during treatment. 
Upper limb cradle 5 includes padded cradle 7 which is padded and contoured 
for the patient's comfort. Elastic soft padding is provided to spread the 
load comfortably. The padding is covered with a soft, breathable material 
for greater comfort. Upper limb cradle 5 also is equipped with straps 8 so 
that the upper limb can be securely held in position. Velcro fasteners on 
straps 8 provide a uniform restraining force. Different size cradles are 
available to suit different limbs and different-size patients, and the 
various size cradles are easily interchanged by removal of fasteners 6. 
The upper limb cradle 5 and upstanding support means 1 are provided with 
upper limb cradle height adjustment means such as slotted holes (not 
shown) provided in seriatim fashion in the upper limb cradle 5 or in 
upstanding support means 2 for the fasteners 6 to pass through to permit 
vertical or other adjustment of the upper limb cradle 5 with respect to 
the upstanding support means 1. The upper limb cradle height adjustment 
means provides adequate adjustment to compensate for the individual 
patient or the particular limb being treated, and the desired range of 
motion that the apparatus will be operating in. The upper limb cradle 
height adjustment means further allows a proper degree of adjustment so 
that the axis of rotation of the joint being treated and the axis of 
rotation of the cradle means B relative to support means A can be made to 
coincide. This is important to assure accurate control of the joint and to 
prevent any chafing action on the limb of the patient. A further feature 
of this invention is the compact, portable nature of the apparatus. In 
view of this, the support means A can be provided with transport means 
(not shown), such as casters, to permit easy movement of the apparatus 
from one room to another and also can be provided with height adjustment 
means (not shown), such as jack screws, to permit adjustment of the height 
of the apparatus with respect to the particular table or chair upon which 
the patient is resting during treatment. 
Cradle means B includes lower limb cradle 9 and actuator rod means. In the 
preferred embodiment the actuator rod means comprises two actuator rods 10 
aligned parallel to one another and positioned along opposite sides of the 
lower limb cradle 10. Lower limb cradle 9 is connected to actuator rods 10 
by tubes 11 which are securely attached to both sides of the lower limb 
cradle 9. Actuator rods 10 are slidable through tubes 11 so that lower 
limb cradle 9 is adjustable along the length of actuator rods 10 to permit 
proper positioning of the lower limb cradle 9 for the patient's comfort. 
Once the lower limb cradle 9 is adjusted to the desired position, it can 
be held in position with respect to actuator rods 10 by thumb screws 14 or 
other similar means. 
The lower leg or the lower arm of the patient is positioned in lower cradle 
9 during treatment. In similar fashion to upper limb cradle 5, lower limb 
cradle 9 includes padded cradle 12 which is padded and contoured for the 
patient's comfort. Elastic soft padding is provided to spread the load 
comfortably. The padding is covered with a soft, breathable material for 
greater comfort. Lower limb cradle 9 is also equipped with straps 13 so 
that the lower limb can be securely held in position. Velcro fasteners on 
straps 13 provide a uniform restraining force. Different size cradles are 
available to suit different limbs and different-size patients, and the 
various cradles are easily interchanged since lower limb cradle is easily 
slidable off actuator rods 10 when the rods have been disconnected at 
either end. Actuator rods 10 are connected to pivot arms 15 so as to pivot 
relative to support means A so that when the upper limb is positioned on 
support means A, preferably in upper limb cradle 5, and the lower limb is 
positioned in lower limb cradle 9, the resulting axis of rotation of 
actuator rods 10 as they are pivoted relative to the support means A 
coincides with the axis of rotation at the knee or elbow joint of the 
lower limb as it pivots relative to the upper limb. This coincidence of 
axis of rotation is of foremost importance since the scheme of operation 
of this invention is to provide a form of motion that patterns the motion 
of the joint. The axis of rotation of actuator rods 10 is at pin 16 which 
pivotally connects actuator rod 10 with pivot arm 15 (pin 16 is best 
illustrated in FIG. 3). Pivot arm 15 is pivotally connected to support 
means A by shaft 17 and is rotatable about shaft 17 to various positions. 
This permits adjustment of pivot arm 15 in order to provide the proper 
clearance for the elbow or knee joint in the various ranges of operation. 
It also permits the axis of rotation of the lower limb about the joint to 
be realigned to coincide with the axis of rotation of the actuator rods 10 
about pin 16 after the actuator rods 10 have been repositioned through a 
nominal angle by positioning means C. After pivot arm 15 is appropriately 
positioned, it is held in position and prevented from further rotation 
with respect to support means A, and more particularly upstanding support 
means 1, by pin 18 which passes through the alignment hole in pivot arm 15 
and through a hole 19 in upstanding support means 1. There are a number of 
holes 19 in upstanding support means 1 arranged in seriatim fashion to 
permit locking of pivot arm 15 in the various positions that may be 
required for the different operating ranges of the apparatus. 
Positioning means C includes actuator frame means 20, rotating means 24 and 
25 to rotate the actuator frame means, and locking means 27 to lock the 
actuator frame means into position after rotation to a desired initial 
treatment position. The function of positioning means C is to position 
cradle means B and thus the lower limb in an initial treatment position 
and at a range of motion which causes the joint to be in a condition which 
is near or at its maximum flexional and/or extensional capacity without 
exceeding the patient's allowable pain tolerance. Actuator frame means 20 
includes at least one and preferably two actuator frame sides 21 aligned 
parallel to one another, actuator frame top 22 secured to and 
interconnecting actuator frame sides 21, and actuator frame bracket 23 
depending from and securely attached to the underside of actuator frame 
top 22. Actuator frame means 20 is pivotally connected to upstanding 
support means 1 by shaft 17. When actuator frame means 20 is pivoted about 
shaft 17 so as to be rotated with respect to upstanding support means 1, 
it causes cradle means B, positioned above and in contact with actuator 
frame means 20, to have substantially coincident pivotal movement. In this 
manner actuator frame means 20 positions cradle means B and thus the lower 
limb at the initial treatment position. Rotating means are provided for 
rotating the actuator frame means 20 to the initial treatment position. 
Rotating means illustrated include hand winch 24, either a double drum 
winch or two winches, and cable 25 attached to actuator frame means 20 by 
clamping means 26 but other similar and conventional means of rotation are 
also envisioned. Once the actuator frame means 20 has been rotated to the 
initial treatment position by the rotating means, locking means 27 are 
provided to lock actuator frame means 20 into position. Locking means 27 
includes a combination lock plate and indexing mark 28 attached to frame 
pin 29 to keep it aligned and locking screw 30 for tightening down. After 
the actuator frame side 21 has been rotated to the initial treatment 
position, lock screw 30 is tightened down to clamp actuator frame side 21 
between lock plate/indexing mark 28 and upstanding support frame means 1. 
The frictional forces developed by this clamping action hold the actuator 
frame means 20 in position. While only one locking device is required to 
safely hold the actuator frame means in position, duplicate locking 
devices can be provided on both sides to permit locking on either or both 
sides of the apparatus. A backup locking means is also provided by using a 
conventional ratcheting device in conjunction with hand winch 24 so that 
as rotation of the actuator frame means 20 takes place it will not be free 
to fall. Actuator frame sides 21 have indexing means, such as peripheral 
calibration marks, on actuator frame sides 21. Indexing mark 28 used in 
conjunction with the calibration marks provide an accurate means to 
accurately and controllably position the actuator frame means 20 at a 
desired intial treatment position. This indexing feature of the invention 
minimizes any chance that the patient's allowable pain tolerance will be 
exceeded since it permits the final position that the patient discontinued 
treatment at in the previous session to be repeated before incremental 
increases in range of motion are attempted. A further advantage of this 
indexing feature is that accurate and controlled increases in the range of 
motion can be effected. Yet another advantage of this indexing feature is 
that the patient's progress can be accurately measured over a period of 
time. 
Reciprocating means D includes push rods 31, and horizontal plate 32 which 
is securely attached to the lower ends of push rods 31. Push rods 31 pass 
through and are slidable with respect to actuator frame top 22, and with 
the aid of sliding bearings are slidable through actuator frame bracket 23 
which keeps the push rods accurately aligned. Eash push rod 31 is 
connected at its upper end to an actuator rod 10, slide bearing 33 and pin 
34. Pin 34 allows actuator rod 10 to pivot in slide bearing 33 during 
normal operation when reciprocating means D function to reciprocate cradle 
means B from the initial treatment position which has been set by 
positioning means C to a variable terminal treatment position. This 
reciprocating movement will provide a corresponding continuous reciprocal 
pivotal movement of the lower limb relative to the upper limb since they 
are positioned in the cradle means B and support means A respectively. 
Variable power means E includes variable weight means 35, variable rewind 
reel means 36, motor means 37, and pulley means (Best shown in FIG. 4). 
Variable weight means 35 has multiple discs 38 that permits incremental 
increases or decreases in the total weight of weight means 35. 
Variable weight means 35 is securely connected to motor means 37 by pulley 
means. The pulley means comprises cable 39 and pulley or sheaves 40 and 
41. Cable 39 is securely attached on one end to variable weight means 35, 
routed over pulley or sheaves 40 and 41 which guide and provide the 
direction of cable motion, and securely attached on the other end to 
rotatable drum 42. Rotatable drum 42 is securely attached to and driven by 
motor means 37, which in the preferred embodiment is a reversible gear 
motor. Variable weight means 35 is securely connected to reciprocating 
means D, and specifically to horizontal plate 32, also by pulley means. 
This pulley means comprises cable 43 and pulley or sheaves 44 and 45. 
Cable 43 is securely attached on one end to variable weight means 35, 
routed over pulley or sheaves 44 and 45 which guide and provide the 
direction for cable motion and securely attached on the other end to 
horizontal plate 32. Pulley 44 rotates on shaft 17. With pulley 44 mounted 
on shaft 17, the stroke of push rods 31 (see FIG. 4 where stroke is 
illustrated by DIM. B and angle .alpha.) will remain constant during 
changes of position of the actuator frame means 20. A bracket 46 supports 
pulley 45 and in securely attached to the underside of actuator frame top 
22. 
Variable rewind reel means 36 is securely connected to reciprocating means 
D, and specifically to horizontal plate 32, by pulley means. The pulley 
means comprises cable 47 and pulley or sheaves 48, 49, and 50. Cable 47 is 
attached to the lower side of horizontal plate 32, then is routed through 
pulleys 48, 49, and 50 to rewind reel means 36. Rewind reel means 36 
ultilizes a constant force torsion spring which provides a relatively 
constant force as cable 47 is wound up or is unwound. The torsion spring 
in rewind reel means 36 can be adjusted to permit variation in the force 
applied to reciprocating means D. 
Variable power means E operably drives reciprocating means D in the 
following manner. Motor means 37 runs in one direction and rotates drum 42 
so that cable 39 winds up on drum 42 causing variable weight means 35 to 
be pulled through an upward stroke as it is lifted in a vertical movement 
through space. Simultaneously, the slack in cables 43 and 47 will be taken 
up as rewind reel means 36 exerts a force to pull reciprocating means D 
through a concomitant downward stroke. The opposite cycle occurs after 
variable weight means 35 has reached its uppermost position as indicated 
in the dotted phantom view of weight means 35 in FIG. 4. Motor means 37 
can then either be de-energized permitting the weight means 35 to slowly 
move down acting through the gear train or the motor 37 can be reversed 
causing weight means 35 to move downward more rapidly to return to its 
initial position. The force of rewind reel means 36 opposes the force of 
variable weight means 35 in its downward stroke, but it does not prevent 
the downward stroke since the force of rewind reel means 36 is adjusted so 
as to be less than the force of variable weight means 35. During the 
downward stroke of variable weight means 35 there is a concomitant upward 
stroke of reciprocating means D as shown in FIG. 4 moving from its 
lowermost position to its uppermost position and represented by DIM. B. 
The force applied to reciprocating means D during its upward stroke will 
be the force of variable weight means 35 minus the force of rewind reel 
means 36. Since both the variable weight means 35 and variable rewind 
means 36 are adjustable as to the amount of force, this adjustment permits 
variation and controlled regulation of the force applied to the 
reciprocating means D. Another embodiment (not shown) of a counteracting 
force which can be used as a substitute for the illustrated rewind reel 
means 36 is a conventional spring positioned over push rods 31 between 
horizontal plate 32 and actuator frame bracket 23. This will result in a 
varying force during both the upward and downward strokes of the 
reciprocating means D. 
The use of the variable power means E, according to this invention, is a 
very important feature of this invention since it permits a convenient 
means of limiting the maximum force applied to reciprocating means D. A 
force is selected so that the patient can resist and successfully overcome 
the force and prevent the knee or elbow joint from further movement. This 
provides a reliable, safe method of operation. Its simplicity is such that 
the patient can understand that he can resist and successfully override 
the force applied by the apparatus and will not be hurt. This is a very 
necessary attribute of the apparatus since a patient who knows that he can 
override the machine will permit treatment closer to his pain tolerance 
and the treatment obviously is much more effective the closer the 
apparatus operates to the patient's ability to withstand pain. Operation 
of the apparatus must approach the threshhold of the patient's pain 
tolerance to be most effective but it must not exceed the threshhold pain. 
Variable stroke means F includes variable timer means on reversible motor 
means 37 and limit rod means. The length of the stroke of reciprocating 
means D, as illustrated by DIM. B in FIG. 4, is a function of the length 
of the concomitant stroke of variable weight means 35, as illustrated by 
DIM. A in FIG. 4. The length of the stroke of variable weight means 35 is 
a function of the length of cable 39 which is wound up on drum 42, which 
in turn is a function of the angle of rotation of drum 42. Since drum 42 
is driven by reversible motor means 37, the angle of rotation of drum 42 
is controllably regulated by use of a variable timer means. Timer devices 
in a gear motor control circuit can be employed to automate the operation. 
Thus, the time that drum 42 rotates in one direction before reversing the 
motor 37 can be varied and controllably regulated. This is the primary 
means of control of the stroke of reciprocating means D. Although not 
shown, instead of a variable timer means on a reversible motor a crank 
mechanism can be used on a gear motor as the variable stroke means. In 
this embodiment, cable 39 can be attached to the free end of a crank 
handle and the stroke can be varied by varying the length of the crank 
handle, or at least by varying the point of connection of cable 39 to the 
crank handle. 
A backup means of limiting the stroke of reciprocating means D is provided 
by using adjustable limit rod means. This means consist of a limit rod 51 
which is connected at its upper end to an acutator rod 10 to a slide 
bearing 33 and a pin 34. Limit rod 51 passes through an opening in the 
actuator frame top 22. The lower end of limit rod 51 is threaded. An 
adjustable stop, such as nut 52, is threaded onto the lower end of limit 
rod 51. Adjustment of the adjustable stop 52 limits the maximum stroke of 
actuator rod 10. (Best shown in FIG. 4) One limit rod 51 is sufficient and 
is connected to one actuator rod 10. However, if desired, two limit rods 
can be utilized, connected to both actuator rods 10. 
Two additional features with regard to variable stroke means F are that the 
speed of the stroke can be varied by using a variable speed gear motor on 
motor means 37 and a brake can be employed in the scheme if desired to 
maintain the limb in a certain position for a given amount of time. 
METHOD OF OPERATION 
One example of a scheme of operation for increasing the range of motion of 
a joint using the apparatus of this invention will be described. However, 
this example is intended as merely illustrative and not exclusive since 
the flexibility of the apparatus permits many treatment variations: 
a. Raise the actuator frame means to an angle which is at or near the 
patient's present maximum range of motion and lock it into position; 
b. Strap the limb to be treated in the upper limb and lower limb cradle; 
c. Reduce the force well below the patient's pain tolerance by removing 
some of the weight discs from variable weight 35 and/or also adjusting the 
torsion spring of the rewind reel 36; 
d. Start the motor 37 so that reciprocating motion begins; 
e. Then increase the force in increments by adding weight discs to weight 
35 until the maximum comfortable range is achieved. At this point the 
patient will be resisting and restricting the motion somewhat and if 
necessary can successfully override the force being applied; 
f. Operate the apparatus until the patient has relaxed sufficiently and the 
soft tissues have stretched adequately so that the reciprocating means 
operates through its full stroke; 
g. Adjust the timer means on the motor 37 so that the stroke of 
reciprocating means is extended so as to move the joint through an 
increased angle of motion; 
h. After an appropriate period of time, raise the actuator frmae means 
through a small increment such as 2.degree. or 3.degree., and adjust the 
stroke and/or force back downward again for this new setting. 
The above process can be repeated as many times as necessary in the process 
of gradually increasing the range of motion in a joint. 
FIGS. 5-7 are illustrative of the method of operating with the apparatus of 
this invention on either the leg or arm. FIG. 5 shows the apparatus set up 
to treat a knee joint with the patient in a sitting position. FIG. 6 shows 
the apparatus set up to treat the knee joint of a patient who is in a 
prone position. When the actuator frame means needs to be positioned in an 
upper position as illustrated in FIG. 6, a removable side extension 21a 
can be attached to actuator frame side 21 for operation. FIG. 7 shows the 
apparatus set up to treat an elbow joint. 
The particular physical therapy apparatus illustrated employs cables, 
pulleys, weights, torsion springs, and electric motors including timer 
controls to provide control of the force applied to and stroke of the 
reciprocating means. However, it is obvious that other arrangements 
including, but not limited to, double acting air cylinders, solenoid 
valves, limit switches, and regulated air pressure sources can provide a 
similar degree of control. 
While a reversible gear motor, cable drum, and cable are illustrated to 
actuate the weight means, it is obvious that other mechanisms such as 
crank assemblies, air or hydraulic operated cylinders, screw thread 
assemblies, or cam mechanisms which are all conventional and extensively 
used in the machinery field can be used as actuation means for the weight. 
While a cable and winch arrangement has been illustrated as rotating means 
to position the actuator frame means, it is obvious that other devices 
such as gears, or chain and sprocket can be similarly utilized. 
While in the foregoing specification a detailed description of a specific 
preferred embodiment of the invention was set forth for the purpose of 
illustration, it is to be understood that many of the details herein may 
be varied considerably by those skilled in the art without departing from 
the spirit and scope of the invention.