Foot pedal motor control

A foot pedal operated motor control is provided for controlling the speed of a motor. The entire motor control circuit is mounted in a foot pedal housing which circuit includes a generally disc shaped potentiometer having a rotatable and a stationary member with the movement of the rotatable member with respect to the stationary member determining the resistance of the potentiometer which controls the current to a motor whose speed is to be controlled. The disc shaped potentiometer has an opening therethrough. A foot pedal is pivotally mounted on the housing overlying the potentiometer and a helical member extends between the foot pedal on one end thereof and into the opening of the disc shaped potentiometer on the other end thereof. When the foot pedal is depressed the helical member is moved linearly turning the rotatable member with respect to the stationary member of the disc shaped potentiometer thereby varying the resistance of the potentiometer which controls the current in the motor control circuit in accordance with the movement of the foot pedal. This control is considerably less expensive than slide type or other rotary type potentiometers. The motion of the foot pedal translates a half inch of linear motion from a full off to full on position on the rotary potentiometer. Accordingly, any wear is spread over 270.degree. of available rotation of the potentiometer. The resistance is varied from 0 to 100,000 ohms providing a wide range of motor control at an inexpensive price. Expensive couplings, linkages and gearings are not required to translate the linear motion of the pedal into a rotary motion for changing the resistance of the potentiometer.

BACKGROUND OF THE INVENTION 
This invention relates to a foot pedal operated motor control circuit, and 
more particularly, to such a circuit which employs an inexpensive rotary 
potentiometer operated by a foot pedal via a helical member. 
A variety of motor control devices which are suitable for controlling 
sewing machines and other small appliances and devices using foot pedals 
have been proposed or utilized but all suffer the disadvantage of being 
bulky, expensive, subject to wear, require elaborate linkages, heat up, 
etc. In such control circuits, the output of the control circuit is 
applied to a motor for controlling its speed. The control is usually 
provided by changing the resistance of the control circuit by switching 
resistors of different values in and out or adjusting the resistance of 
the particular circuit normally using a potentiometer. The contacts and 
the resistance elements of such control circuits are subject to wear, 
arcing, heating and may provide a shock hazard to the user. Furthermore, 
portions of the control circuit are housed in different units and if 
potentiometers are used, either the linear or rotary type, elaborate 
linkages are generally required for converting the linear motion of the 
foot pedal into a suitable linear or rotary motion for operating the 
potentiometer. Furthermore, the motor control function may not provide 
smooth changes in speed, particularly as the contact elements wear or 
suffer thermal damage. In addition, these controls are sometimes complex 
and expensive. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a compact, 
reliable and inexpensive foot pedal motor control which is particularly 
suitable for controlling the speed of sewing machines, motor tools and 
other small appliances and apparatus. 
A further object of this invention is to provide a new and improved motor 
control which produces a smooth, accurate and a wide range controllable 
change in motor speed. 
A still further object of this invention is to provide a new and improved 
foot pedal operated motor control which is exceedingly simple, safe in 
operation and provides quality performance with no shock hazard to the 
user. 
Still another object of this invention is to provide a new and improved 
foot pedal operated motor control in which the complete motor control and 
control circuit are housed in the foot pedal itself. 
In carrying out this invention in one illustrative embodiment thereof, a 
foot pedal operated motor control is provided for controlling the speed of 
a motor which includes a housing having a rotary potentiometer mounted 
therein and an opening in the potentiometer. A foot pedal is pivotally 
mounted on the housing. The helical member is coupled between the foot 
pedal and the opening in the potentiometer for translating the linear 
motion of the helical member to a rotary movement in said rotary 
potentiometer for producing a change in resistance when the foot pedal is 
depressed whereby the resistance change in the rotary potentiometer 
controls the current applied to a motor for controlling the speed thereof. 
The potentiometer is also coupled to a line switch for placing a line 
voltage on the motor control circuit when the helical member actuates the 
potentiometer when the foot pedal is depressed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a foot pedal 10 is pivotally mounted on a pivot 12 
to a housing 14. The foot pedal 10 has an upper covering 16 thereon 
containing a saw toothed pattern 18 for providing a nonslip surface which 
may be contacted by the foot of the user. A power cord 20 and a motor 
control cord 22, which is adapted to be coupled to the motor to be 
controlled, are both coupled into the interior of the housing 14. 
As will be more clearly seen from looking at the interior of the housing, 
as shown in FIGS. 3 and 4, a motor control circuit is provided which is 
generally identified with the reference numeral 25. The motor control 
circuit 25 is mounted on a circuit board 24 which is attached to a base 26 
by bolts 28. The motor control circuit 25 may be any suitable type for 
varying the current, and therefore controlling the speed of a motor in 
accordance with the application and the type of motor which is employed. 
The specific details of the motor control circuit 25 are considered 
conventional and do not form a part of the present invention. However, the 
rotary potentiometer which forms a part of the motor control circuit 25 
and the helical member for driving the potentiometer ultimately control 
the current to the motor being controlled and accordingly constitutes a 
part of the present invention and is described in detail hereinafter. 
The foot pedal 10 may be of any suitable type and performs the function of 
actuating the motor control circuit 25 when depressed. As will best be 
seen in FIG. 3, the foot pedal 10 is pivotally mounted on a pivot 12 
extending through the housing 14. A compressible spring 30 is positioned 
on protruding studs 32 and 34 on the foot pedal 10 and housing 14, 
respectively. The spring 30 normally biases the foot pedal 10 upward and 
the motor control circuit 25 is normally inactive in this position. Also, 
when the foot is released from the foot pedal 10, the spring 30 returns 
the foot pedal 10 to its upper or inactivated position turning off the 
motor control circuit in a manner to be described. 
A rotary potentiometer, referred to generally with the reference numeral 
40, includes a rotary element 42, a stationary variable resistance element 
44 and a metallic base 46 having mounting legs 48 (see FIG. 6). Electrical 
connector terminals 50 which are mounted on a phenolic board extension 52, 
which also forms a part of the stationary member 44, provides a means for 
making electrical connections to and tapping off the variable resistance 
which occurs between the terminals 50. The potentiometer 40 has an opening 
or slot 54 extending through the rotary element 42 and accordingly through 
the entire potentiometer 40. The rotary element 42 also has a downwardly 
extending leg of projection 56 which in the inactive position of the 
potentiometer bears on a pivotal spring arm 58 of a line switch 60. When 
the rotary element is actuated and turned, the leg 56 rotates clockwise 
releasing the spring arm 58 which pivots outwardly closing the contacts of 
switch 60 placing power from the line cord 60 on the motor control circuit 
25. 
A suitable type of rotary potentiometer 40 for the present application and 
the one which has been described is type U 201 manufactured by CTS of 
Elkhart, Ind. 
In order to translate the linear movement of the foot pedal when it is 
actuated by the foot of the user into a rotary motion, a helical member 62 
is utilized which is coupled between the foot pedal 10 and the opening 54 
of the potentiometer 40. As will best be seen in FIG. 6, the helical 
element 62 has an eyelet 64 formed on one end thereof which is mounted on 
a suspended shaft 66 on the underside of the foot pedal 10. The other end 
64 of the helical member 62 is flat and extends through the opening 54 in 
the rotary element 42 of the rotary potentiometer 40. Accordingly, eyelet 
end 64 of the helix is fixed to the foot pedal 10 while the flat end 64 
fits through the opening 54 and is free to move in and out thereof. 
In operation when the foot pedal 10 is depressed the helical member 62 
moves linearly and is forced down through the opening 54 in the rotary 
member 42 of the rotary potentiometer 40 rotating the rotary member 42 
because of the helical curvature of the helical member 62. At the same 
time the leg 56 has released and closed the contacts of the switch 60 
placing power on the motor control circuit 25. The amount of rotation of 
the rotary member 42 of the potentiometer determines the resistance of the 
rotary potentiometer 40 which controls the current applied to the motor 
from the motor control circuit 25. This arrangement is very advantageous 
because the helical member 62 translates a half inch of linear motion 
applied to the foot pedal 10 from full off to a full on position of the 
rotary potentiometer 40. The foot pedal control spreads the value of 
resistance of the rotary potentiometer over a 270.degree. arc which limits 
the wear on the rotary potentiometer. The potentiometer, which is 
relatively inexpensive, provides a change in resistance of 0 to 100 kohms 
over a 270.degree. angle. The control thus provided is smooth, even and 
spread over a relatively long arc. 
As has been indicated, a conventional motor control circuit may be 
utilized. A simplified version of an electronic motor control circuit is 
illustrated in FIG. 7 which includes the line switch 60, the potentiometer 
40, a motor 70 which is to be controlled, a capacitor 76, a triac 72 and a 
diac 74. Both the triac 72 and the diac 74 are bidirectional 
semi-conductors, and accordingly the circuit illustrated in FIG. 7 is a 
full wave circuit. 
In operation, depression of the foot pedal 10 varies the resistance of the 
rotary potentiometer 40 changing the voltage applied to capacitor 76 and 
thus to the bidirectional diac switch 74 which controls the phase of the 
firing of the triac 72 and accordingly varies the current applied from the 
AC line to the motor 70 to control the speed thereof in accordance with 
the setting of the potentiometer 40. As has been previously stated, 
different types of motor control circuits can be employed with greater 
degrees of sophistication where desired. However, the translation of the 
linear to the rotary motion afforded by the foot pedal 10 and its 
associated helical member 62 would be employed in the control of and the 
variation of the resistance in such circuits. 
The present motor control circuit which is foot pedal operated and 
translates a very short throw or depression of the foot pedal into a 
270.degree. rotation of a rotary potentiometer for changing the resistance 
thereof and varying the current which is applied to the motor for 
controlling the speed thereof offers a very simple, inexpensive 
construction employing a very cheap rotary potentiometer. The circuit is 
simple, accurate, easy to operate and easy to control. Since a large angle 
is used by the potentiometer for the variation of its resistance, less 
wear and tear results improving the reliability of the circuit. It is also 
a decided advantage in having the entire motor control circuit mounted in 
the foot pedal per se which offers the advantage of simplicity, as well as 
a compactness. 
Since other changes and modifications varied to fit particular operating 
requirements and environments will be apparent to those skilled in the 
art, the invention is not considered limited to the examples chosen for 
purposes of illustration, and covers all changes and modifications which 
do not constitute a departure from the true spirit and scope of this 
invention.