Coupling device for the play-free connection of a precision potentiometer with a movable machine part

A coupling device is provided for coupling the movable member of a machine to a potentiometer to convert sliding movement of the member into proportionate movement of potentiometer. The device includes a first rod which is attachable to the movable machine member and a second rod which is connectable to the potentiometer. A ball-shaped slide is attached to the first rod and a planar abutment is attached to the second rod. The glide piece and the abutment are in abuting contuct with one another. A biasing spring is provided which applies pressure, in a working direction, to the glide piece to thereby maintain the glide piece and the planar abutment in intimate engagement with one another. This arrangement forms a joint connection between the first and second rods which enables transmission there between of only translational movement.

BACKGROUND OF THE INVENTION 
The present invention relates to a coupling device and more particularly to 
a coupling device which permits play-free connection of a precision 
potentiometer and a movable machine part. 
It is known in the art that a determination of the movement of machines, 
for example the relative displacement movement of a machine setting 
member, is needed to control shifting movement of the machine. When 
translatory shifting movement is to be determined by a path measuring 
device, constructed as a potentiometer, the machine and the potentiometer 
must be precisely connected to one another and bought into an almost 
parallel relationship so that the shifting movement of the machine 
elements can be translated to the slider of the potentiometer. Due to both 
required tolerances and the very exact guidance which the path measuring 
device requires, so that measuring can be carried out properly, problems 
occur in converting the shifting movement into potentiometer displacement 
that have not been eliminated heretofore. 
When the movable parts of the potentiometer and the machine are rigidly 
coupled, rapid destruction in the potentiometer region occurs, resulting 
in a continuously increasing measurment error. Loose coupling, however, 
results in inaccuracies in the conversion of the translatory shifting 
movement and, further, does not offer the necessary degree of freedom for 
proper operation and transmission of translatory movement 
Accordingly, one object of the present invention is to provide a coupling 
device which transmits, in a play-free manner, the translatory movement of 
a machine part to a precision potentiometer, and which concomitantly 
permits free motion in other directions, namely: parallel displacement in 
the X and the Y direction, whereby the Z direction is the direction of the 
to-be measured play-free movement. 
Another object of the present invention is to provide such a device which 
is substantially easy and inexpensive to install, and which can be 
installed almost completely by unskilled labor without the occurrance of 
measuring errors or other problems. 
BRIEF DESCRIPTION 
The coupling device of the present invention connects a movable portion of 
potentiometer with a machine element capable of performing a translatory 
setting movement. The coupling device permits forces exclusively in the 
direction of sliding movement which guarantees a play-free transmission of 
forces. In all other conceivable directions of movement, the device is 
essentially both force-free and backlash-free so that the potentiometer is 
not influenced by any forces which do not contribute to the desired 
setting movement. 
In one embodiment of the present invention a coupling device capable of 
providing a play-free connection, in a working direction, of a movable tap 
of a precision potentiometer and a movable setting member of a machine is 
provided. The device includes a ball-shaped glide piece which is secured 
to one of the movable parts and a planar abutment which is secured to the 
other movable part. A pre-tensioning spring is provided which is 
positioned such that it is capable of pressing the glide piece and the 
planar abutment against one another to thereby obtain the play-free 
connection. 
The components of the coupling device are not subjected to bending due to 
their arrangement relative to one another. The coupling device is thus 
capable of withstanding: parallel displacement in the entire X-Y 
coordinate plane; circular movement; planar movement; tumbling movement; 
or a combination of all the foregoing movements. 
In one embodiment of the present invention, the glide piece is sandwiched 
between planar abutments. The glide piece can be a hardened steel ball and 
the abutments can be flat ground sapphire stones. One of the stones can be 
pressed by the pre-tensioning spring so that the steel ball is held 
between the two sapphire stones without any play. This arrangement 
provides a joint-like connection between the steel ball and the oppositely 
located sapphire stones. The sapphire stones may be mounted in the sliding 
element of the potentiometer, and the setting member of the machine is 
connected to the steel ball using a pin. The steel ball, held in play-free 
position by the stones is suitable for the transmission of translatory 
movement, but is movable in all other directions. Thus, the steel ball can 
freely shift upwardly, downwardly, and rearwardly within a space defined 
by the two sapphire stones. The ball can perform both rotary movements 
about itself and tilting movements about the pin connected to it without 
causing a change in or influencing the translatory path to be measured. 
Thus actuation of a longitudinal potentiometer, acting as a path measuring 
device, is possible without any substantial force acting upon the mounting 
thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings and more particularly to FIG. 1, in one 
embodiment of the present invention the coupling device 1 is rod-like 
having a pronounced longitudinal extension. Coupling device 1, as shown in 
FIG. 1, is usable with a longitudinal potentiometer of small dimensions. 
By way of example, the potentiometer may be constructed such that an 
extension 2a of a first partial rod 2 of coupling device 1 serves as a 
pull rod of the potentiometer (not shown) which extends through the entire 
potentiometer body and which is for example, journaled at both ends by 
means of appropriate glide bearings to thus support a slider, connected in 
stationary manner thereto for movement over the resistance path of the 
potentiometer. Thus, proportional longitudinal shifts in the rod 2a result 
in proportionate changes in resistance. A second partial rod 3 is provided 
which, as noted more specifically below, is connected in absolutely 
play-free fashion with the first partial rod 2. The rod is free to move in 
all other directions so only longitudinal forces representing translatory 
motion can be exerted upon the first partial rod 2 which is connected with 
the potentiometer (i.e., in a direction which corresponds to the axial 
extension of the coupling device 1). At its other end, the second partial 
rod 3 has connecting means, preferably two discs 4 and two nuts 5a and 5b 
to allow direct connection of the rod to the movable machine setting 
element (not shown) which undergoes the translatory movement. 
The first partial coupling rod 2 is provided, at its end portion facing the 
second partial rod, with a cylindrical recess 6 for the formation of a 
joint. Recess 6 can be formed by an at least partial cylindrical tube 7 
which is open at both ends and which is screwed onto the first partial rod 
at threads 8 and which has, at the other end a central circular opening 9. 
Opening 9 is formed by a ring flange 10 having an inner shoulder 10a 
against which one end of a pre-tensioning spring 11 abuts. A rod-like 
extension 12 of the second partial rod extends telescopically into the 
recess 6 through the opening 9. At its inner end, extension 12 had an 
enlarged diameter disc 13 upon which the pre-tensioning spring 11 bears. 
Also connected to the inner extension 12, is a glide piece 14 in a holder 
15. Holder 15 can be a suitable adhesive or cement capable of holding the 
glide piece 14 in position. Preferably, glide piece 14 is a hardened steel 
ball which abuts against a planar abutment or anvil 16 under the pressure 
of pre-tensioning spring 11. 
In a preferred embodiment the abutment 16 comprises a sapphire stone which 
is held in an appropriate setting 17 at the end of recess 6. The diameter 
of extension 12 is smaller than the diameter of opening 9 by a desired 
amount. The second partial rod telescopically extends into the recess 6 
through opening 9. Further, the diameter of the disc 13 is smaller than 
the recess inner diameter, by a predetermined amount. Since the 
pre-tensioning spring 11 is constructed as a pressure or biasing spring, 
it produces a completely play-free abutment of the hardened steel ball 14 
at the planar face of the sapphire stone, or abutment 16 so that the ball 
14 is always in contact with the abutment. 
That is, the force of the pre-tensioning spring 11 holds the steel ball on 
the surface of the sapphire stone under any conceivably occuring 
frictional or accelerational influences. However, the pre-tensioning 
spring 11 is yieldable in a radial direction such that it has no, or only 
negligible, restoring forces. 
The second partial rod 3 can move freely relative to the first partial rod 
2. It can be subjected to limited parallel displacement in the direction 
of the X-Y coordinate plane, assuming the Z direction corresponds to the 
translatory measuring movement. 
Additionally, the coupling device of the present invention permits rotary 
or circular movement of the second partial rod about its central axis 
corresponding to the arrow A as well as any tumbling planar movements 
along the arrows B. The second partial rod 3 is completely movable in all 
the aforementioned directions and, further, the second rod is loosely held 
with respect to the first rod and thus transmits none of the foreign 
forces which result from the movements to the potentiometer. That is only 
translational or longitudinal movement of rod 3 is communicated to the 
potentiometer. 
Due to the respective spacings of the disc 13 and the inner wall of the 
tube, and of the diameter of opening 9 with respect to the diameter of 
extension 12 of the second partial rod, in addition to parallel movement 
in the X-Y direction, the two rods can perform tumbling or pivotting 
movements relative to one another, at least until the disc 13 and the rod 
extension 12 contact the surrounding walls. Such displacement of the 
second partial rod results in no axial position change. Axial position 
change during tumbling or pivotting movement is negligible because of the 
respective sizes of the elements, and is one measure below the measuring 
accuracy of the system. 
Both the hardenened steel ball and the planar sapphire stone upon which the 
ball rides are selected to keep frictional influences as low as possible 
and to avoid wear. 
In another embodiment of the present invention, shown in FIGS. 2a and 2b, 
an outwardly extending slider 20 of potentiometer is provided. The slider 
20 can be shifted over the entire length of the potentiometer, 
corresponding to the path direction to be measured. On an upper portion, 
the slider carries the coupling device. 
The main elements of the coupling device include a ball-shape glide piece 
which preferably is a hardened steel ball 14' and two planar abutments 
located on opposite sides of the ball. Preferably the planar abutments are 
sapphire stones 16a' and 16b' which have their sides facing the steel ball 
14' so as to provide a completely plane ground abutment face for the steel 
ball 14'. To insure reliable play-free holding of the steel ball between 
the two sapphire stones, one sapphire stone is held in a suitable holder 
22 in a stationary manner, while the other sapphire stone is mounted in 
holder 23 so as to be longitudinally shiftable in a direction towards the 
steel ball. 
As shown in the drawings, stone 16b' is mounted in holder 23 and is under 
the influence of a pre-tensioning spring 24. Holder 23 is provided with an 
inner bore 23a which receives pre-tensioning spring 24 and which forms a 
slideable bearing for sapphire stone 16b'. Sapphire stone 16b' is 
practically stationary in its mount, and it is essentially immobile so 
that a pressure force acting upon it, via the spring 24, is such that 
there is always a completely play-free abutment of the steel ball 14' 
against the two stone surfaces. The stone surfaces can be set flush into 
the associated wall regions of their holders to form with same a cage-like 
receiver space 25 for the steel ball 14' in which the steel ball can 
otherwise move--i.e. in turn, shift and freely perform combined movement 
in all conceivable directions without generating restoring forces. The 
ball is thus loosely held between the abutments 16a' and 16b' so that it 
can absorb forces related to the movements. 
As shown in FIGS. 2a and 2b the measuring direction is denoted by the 
double-headed arrow Z, and the double-headed arrows X and Y designate the 
free shifting movements in the X-Y coordinate plane which the steel ball 
can execute within its cage 25. The ball is thus held in play-free 
abutment against the two sapphire stones. The double-headed arrow B of 
FIG. 2a denotes pivotting or tumbling movements performable by the ball 
and the arrow A denotes such rotary or circular movement performable by 
the ball. Ball 14' is loosely journaled and thus can move in the 
directions X, Y, B and A and can absorb these movements. Foreign forces 
resulting from these movements are not transmitted to the potentiometer. 
In order to transmit movements resulting from the setting member of the 
machine element, via ball 14' to the slider 20, ball 14' has a pin 26 
connected to it. Pin 26, at an upper portion thereof is provided with an 
outer thread onto which tensioning nuts may be threaded to secure it to 
the setting member of the machine element.