Tremor suppressing hand controls

A hand control capable of suppressing tremors and other unwanted vibrations is disclosed which incorporates viscous damping in two degrees of freedom to mechanically filter the forces applied by the user's hand. To suppress pathological intention tremors, the damping characteristics are chosen so as to selectively reduce the amplitude of movements at or above about 3 Hertz. The hand control includes a chamber filled with a viscous fluid, a position-sensing actuator assembly and a damping element connected to the actuator and disposed within the chamber to suppress involuntary movements of the actuator. The volume of the chamber, size of the damping element and viscosity of the fluid are chosen to achieve a damping constant of about 2 to 20 lbf-sec/ft., preferably from about 5 to about 15 lbf-sec/ft. The viscous fluid is preferably a silicone oil having a viscosity of about 300,000 to about 900,000 cstokes.

The technical field of this invention is hand controls which generate 
electrical signals in response to movement of an operator-actuated handle 
and, in particular, hand controls which damp involuntary tremors or other 
vibrations during use. 
A common form of pathological tremor is known as intention tremor and is 
characterized by random, oscillatory muscle activity superimposed upon 
intended motion during the performance of voluntary acts. In severe cases, 
the amplitude of intention tremor can be so great as to obscure the 
desired motion. It is estimated that almost one million people in the 
United States alone are affected by intention tremor. 
Those who rely upon automated wheelchairs and similar vehicles for mobility 
are particularly troubled by intention tremor. Conventional hand controls 
for electrically powered wheelchairs are ill-suited for disabled persons 
who also suffer from tremors. Such controls typically translate the user's 
tremors into random and unwanted wheelchair motion, causing fatigue, 
frustration and, sometimes, danger to the user. 
There exists a need for better hand control mechanisms for those afflicted 
with intention tremor. Hand control mechanisms which could ease the 
operation of wheelchairs and other vehicles would satisfy a long-felt need 
in the field. Even among the able-bodied population, control interfaces 
which could suppress tremors or other unwanted vibrations would improve 
performance of a wide variety of manually controlled operations. 
SUMMARY OF THE INVENTION 
A hand control capable of suppressing tremors and other unwanted vibrations 
is disclosed which incorporates viscous damping in two degrees of freedom 
to mechanically filter the forces applied by the user's hand. To suppress 
pathological intention tremors, the damping characteristics are chosen so 
as to selectively reduce the amplitude of movements at or above about 3 
Hertz. 
In one preferred embodiment, the hand control includes a chamber filled 
with a viscous fluid, a position-sensing actuator assembly and a damping 
element connected to the actuator and disposed within the chamber to 
suppress involuntary movements of the actuator. In the illustrated 
embodiments, the damping element is a spherical ball. The volume of the 
chamber, size of the ball and viscosity of the fluid are chosen to achieve 
a damping constant in the range of about 2 to 20 lbf-sec/ft., preferably 
from about 5 to about 15 lbf-sec/ft. The viscous fluid is preferably a 
silicone oil having a viscosity preferably of about 100,000 to about 
900,000 cstokes, more preferably, of about 400,000 to about 700,000 
cstokes. 
The position sensing actuator assembly can be formed, for example, by 
connecting the actuator handle via yokes to a pair of orthogonally 
positioned potentiometers. As the handle is moved, it moves the yokes with 
it. The yokes are attached to the potentiometers such that any movement of 
the yokes results in a change in the resistance of the potentiometers. 
For wheelchair control as well as other applications, the hand control 
mechanism can also include a fast stop mechanism which allows the damping 
to be bypassed. In an illustrated embodiment, a control button is 
incorporated into the actuator handle which must be depressed for handle 
movement to be effective (e.g., in producing wheelchair movement); unless 
the user depresses the button, the motor is not engaged. Conversely, when 
the button is released, the wheelchair automatically comes to a halt. 
The hand control position sensors (or the subsequent signal processing 
circuitry) can also include a dead zone in which motion of the actuator is 
not translated into changes in output signal. Such a zone about the center 
area of handle movement is preferred to eliminate spurious movements of 
the vehicle or other controlled system when the user accidentally or 
unintentionally displaces the handle slightly from its upright (or other 
null point) centering position. In some instances, this dead zone can 
eliminate the need for centering (return) springs. 
The invention will next be described in connection with certain illustrated 
embodiments. However, it should be clear that various changes, additions 
and subtractions can be made by those skilled in the art without departing 
from the spirit or scope of the invention. For example, although the 
invention is described principally in connection with wheelchair 
operations, it should be clear that the hand controls can also be adapted 
to meet other needs of tremor-disabled persons. Devices according to the 
present teachings can be applied to the control of computer screen 
cursors, hand operated communication devices, home appliances, etc. 
Additionally, the present invention can also be applied to suppress 
involuntary motions by even the able bodied operator of a hand control. In 
delicate or dangerous, remote-control situations, hand controls according 
to the present invention can be employed to reduce the possibility of 
mishap. Surgical instruments, robot arms, and various other delicate 
devices can benefit from the present teachings. Moreover, the invention 
can also be used to suppress jolts and other spurious external vibrations, 
for example, in rough terrain vehicles, airplanes and other similar 
applications.

DETAILED DESCRIPTION 
In FIG. 1, a hand control 10 is shown having a chamber 12 filled with a 
viscous fluid 14, such as silicone grease (e.g., Dow Corning 200 fluid 
--600,000 cstokes). Disposed within the fluid is a shaft 16 carrying a 
drag element 18 which cooperates with the fluid 14 to damp displacements 
of shaft 16. The drag element is preferably a sphere in order to achieve 
equal damping action in all directions as it moves through the fluid. For 
a chamber approximately 5 inches in diameter, the spherical drag element 
can be about 3/4 to 1 inch in diameter. 
The shaft 16 is coupled to the chamber 12 via a spherical (or partially 
spherical) pivot element 20 and a cooperating annular socket 22. The 
pivoting ball element 20 and the socket 22 include mating surfaces which 
allow the shaft to move freely (e.g., through about 30 degrees) in each of 
two degrees of freedom. A boot or low friction seal 44 can also be 
incorporated between the upper surface of the socket 22 and pivoting 
element 20 to prevent fluid leakage should the device be oriented in a 
direction other than upright and to exclude dirt from the pivoting ball 
and socket joint. Handle 34 is disposed on the upper end of shaft 16 to 
allow the user to pivot the shaft 16. 
Activation switch 38 is incorporated into handle 34 to control movement of 
the motor-driven machine 50. A boot or other hermetic seal 36 can be 
employed to exclude dirt from the position sensing mechanism 24. A plug 40 
can be incorporated for filling and draining the chamber 12. 
An upper casing 42 is disposed above the chamber 12 to define a housing for 
a position sensing mechanism 24. In the illustrated embodiment, the 
position sensing mechanism includes a first potentiometer 26 and a second 
potentiometer 28 having first and second input shafts, respectively, 
positioned orthogonally to each other. 
Wires 26A, 28A and 38A, from first potentiometer 26, second potentiometer 
28 and activation switch 38, respectively, provide directional and control 
signals for the motor driven machine 50. 
In FIG. 2, the position-sensing mechanism is shown in more detail, 
including the first and second potentiometers 26, 28 coupled to the shaft 
16 by the first and second orthogonal yokes 30, 32, respectively. Each of 
the yokes 30, 32 includes a longitudinal slot 46, 48 through which the 
shaft passes. The yokes are mounted to independently pivot with movement 
of the shaft 16. Movement of the yokes 30, 32 results in changes of the 
resistance of the potentiometers 26, 28 via rotation of their input 
shafts. Return springs (not shown) can also be incorporated to bias the 
handle and return it to a reference point. 
In the illustrated embodiments, the reference point is dead center upright 
and any movement therefrom results in a varied electrical resistance 
exhibited by the first and second potentiometers 26, 28. The combination 
of such signals allows the user to provide a full range of movement 
control instructions in two dimensions (e.g., forward and backward, left 
and right). 
It should be appreciated, however, that hand controls according to the 
present invention need not be restricted to upright applications. The 
device can be oriented such that the null point for the shaft may be 
horizontal or at any other angle, including upside down from the 
illustrated embodiment, so long as the boot or seal 44 is adequate to 
prevent fluid leakage. 
Regardless of the orientation of the dead center reference point, it may be 
preferable to incorporate a dead zone about the reference point to 
eliminate unintended deviations from zero output when the user accidently 
or unintentionally displaces the handle through a small angle as well as 
when the device does not incorporate return springs or the like. Such a 
dead zone can be accomplished by non-linear resistance elements in the 
potentiometers 26, 28 so that slight rotations of the input shafts do not 
change their resistance. Alternatively, processing of the potentiometer 
signals with threshold sensing can achieve the same dead zone effect. 
It should also be appreciated that the yoke and potentiometer mechanism can 
be replaced by alternative structures. For example, four or more on-off 
push button switches disposed about the shaft can be employed such that 
displacement of the shaft activates one or more of the buttons. Such a 
mechanism would also incorporate a dead zone, insofar as a finite 
displacement from the reference position is necessary in order to cause 
the switches to close. 
The hand control described above can have a diameter of about 4.5 inches, a 
height of 6.5 inches, and can weigh under 3 pounds. It is ideally suited 
for control of electric wheelchair motors to convert the user's hand 
motions into directional control signals. However, the hand controls 
disclosed herein can also be used in the control of vehicles generally, 
such as motorized vans, rough terrain vehicles, aircraft, flight 
simulators and the like. Hand controls according to the present invention 
can also be used to facilitate fine control of robot arms, particularly in 
delicate or dangerous, remote control applications. Devices along the 
lines of those disclosed herein may also find use in controlling the 
direction of endoscopes and catheters during surgery or medical diagnosis, 
as well as controlling X-Y translation stages for semiconductor device 
fabrication operations and the like.