Methods and apparatus for translating electric motor rotation into linear travel

Methods of operating, and apparatus including, a rotary electric motor to translate rotation of the motor into linear travel with the aid of a linearly traveling device. This linearly traveling device is restrained against rotation at points peripherally distributed relative to the device. In particular, there is a pair of interfitting parts including a linear keyplate and keyway at each of the peripherally distributed points. One of these interfitting parts is connected to the linearly traveling device and the other of these parts is maintained stationary relative to that one interfitting part. One of the linear keyplates may be provided with a first scale indicating the linear travel in a first system of measurement, such as the metric system, and another linear keyplate may be provided with a second scale indicating the linear travel in a second system of measurement, different from the first or metric system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The subject invention relates to electric motors, actuators and actuating 
methods and, more specifically, to methods of operating or utilizing 
electric motors, and to apparatus including electric motors, as well as to 
their design and operation. 
2. Disclosure Statement 
This disclosure statement is made pursuant to the duty of disclosure 
imposed by law and formulated in 37 CFR 1.56(a). No representation is 
hereby made that information thus disclosed in fact constitutes prior art, 
inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends 
on uncertain and inevitably subjective elements of substantial likelihood 
and reasonableness, and inasmuch as a growing attitude appears to require 
citation of material which might lead to a discovery of pertinent material 
though not necessarily being of itself pertinent. Also the following 
comments contain conclusions and observations which have only been drawn 
or become apparent after conception of the subject invention or which 
contrast the subject invention or its merits against the background of 
developments subsequent in time or priority. 
In recent years, mechanical actuators have reached a high state of 
perfection. By way of example, reference may in this respect be had to 
U.S. Pat. No. 4,174,575, by Kyohiro Nakata, issued Nov. 20, 1979, for 
Measuring Instrument, and now assigned to the assignee of the subject 
patent application or patent. One of the measuring instruments disclosed 
in that patent is a differential micrometer having an adjustment precision 
of one-half micrometer or 0.0005 millimeters. While that micrometer is, of 
course, very useful as a measuring instrument, it also serves as a 
high-precision actuator in such delicate applications an optical component 
adjustment in holographic or other laser beam utilization systems. A 
disadvantage of using differential micrometers as component actuators is, 
however, that they are manually operated. 
Attempts have thus been made to provide electrically energized actuators 
which could take the place of the manually operated micrometer type. 
Accordingly, a small electric motor with reduction gearhead has been 
accommodated in a tubular housing, for axial movement. The output shaft of 
the gearhead was attached to a threaded spindle which extended through an 
internal thread in a front piece of the housing. To inhibit rotation of 
the motor and gearhead, a longitudinal keyway was provided in the housing, 
while an antirotation device having a key projection running in the keyway 
was attached to the gearhead. The motor through its gearhead rotated the 
threaded spindle, which thus at least in theory would translatorily move 
out of and alternatively into the internally threaded front piece of the 
housing. 
In practice, the latter approach has several problems. For one thing, the 
key device would pivot or cant when running under load, thereby incurring 
side loads from torquing. On the other hand, attempts at reducing the side 
load exposed the gearhead to disintegration when the spindle was reaching 
its extremity of translatory motion. 
SUMMARY OF THE INVENTION 
It is a general object of this invention to overcome the disadvantages and 
to meet the needs expressed or implicit in the above disclosure statement 
or in other parts hereof. 
It is a germane object of this invention to provide improved motorized 
micrometers and actuators. 
It is a related object of this invention to provide improved devices for 
converting rotation into translatory motion. 
Other objects of this invention will become apparent in the further course 
of this disclosure. 
From one aspect thereof, the subject invention resides in a method of 
operating or an apparatus including a rotary electric motor in a tubular 
housing and, more specifically, resides in the improvement comprising, in 
combination, the steps of, providing two diametrically opposed keyways in 
said tubular housing, providing a keyplate for or means for, translating 
rotation of the motor into linear travel, attaching the keyplate to the 
motor for axial movement of the motor in the housing, and restraining such 
keyplate against rotation at two points diametrically opposite each other 
relative to such keyplate, by providing the keyplate with two keys located 
opposite each other and projecting into the diametrically opposed keyways, 
with the two keys and keyplate being provided as one solid unit. 
From another aspect thereof, the subject invention resides in an actuator 
or other apparatus, including a rotary electric motor and, more 
specifically, resides in the improvement comprising, in combination, a 
tubular housing having diametrically opposed keyways therein, means 
including a linearly traveling keyplate in the housing for translating 
rotation of the motor into linear travel, means for attaching the keyplate 
to the motor for axial movement of the motor in the housing, means for 
restraining the linearly traveling keyplate and motor against rotation at 
two points diametrically opposite each other relative to the keyplate, 
including two keys diametrically opposite each other and projecting into 
the diametrically opposed keyways, the two keys and keyplate being in one 
solid unit. 
Other aspects of the invention will become apparent in the further course 
of this disclosure, and no limitation to any invention, aspect, scope, 
object, feature, combination, step or component is intended by this 
summary of invention.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The motorized linear actuator 10 shown in FIGS. 1 to 4 has a cylindrical 
electric motor 12 axially movable in a hollow-cylindrical housing 13. The 
motor 12 has a reduction gearhead 14 attached. The gearhead has an output 
shaft 15 which rotates upon energization of the motor 12 via motor 
terminals 16 and 17. 
The tubular actuator housing 13 has an end cap 19 removably fitted in an 
end portion thereof. By way of example, the tubular housing 13 may be of a 
metal, such as aluminum, while the end cap 19 may, for instance, be of a 
plastic material press fitted into the tubular housing. 
In the illustrated embodiment, a phone jack 21 or similar receptacle 
extends through the end cap 19 into a terminal box having terminals 23 and 
24 protruding from it. These terminals 23 and 24, which receive electric 
energizing current for the motor 12 through the jack 21, are connected to 
the motor terminals 16 and 17 via a couple of wires contained in a cable 
25 which is long enough to permit axial travel of the motor 12 in the 
tubular housing 13. 
The actuator 10 translates rotation of the motor 12 or gearhead output 
shaft 15 into linear travel of a threaded spindle 27. 
To this end, the spindle 27 has an external thread 28 meshing with an 
internal thread 29 of a nose or front piece 31 of the actuator 10. The 
front piece 31, in turn, is threaded into a front end of the tubular 
housing 13 at 32. 
The actuator 10 further includes a linearly traveling device 34 for 
translating rotation of the motor 12 into linear travel of the spindle 27. 
The linearly traveling device 34 includes a keyplate 35 having at least 
two keys 36 and 37 projecting, respectively, into keyways 38 and 39, 
provided in the tubular housing 13. 
The keyplate 35 is attached to the gearhead 14 by such fasteners as screws, 
one of which is apparent at 41 in the cutout portion of FIG. 2. In this 
manner, rotation of motor 12 and gearhead 14 relative to the keyplate 35 
and thereby to the tubular housing 13 is inhibited. On the other hand, the 
threaded spindle 27 rotates as it thrusts forward out of, and as it 
retracts into, the front piece 31. However, such rotation is not 
essential, and the broad aspects of the subject invention are not intended 
to be so limited. Rather, the scope of the subject invention extends to 
apparatus in which the thrusting element of the actuator merely moves 
linearly without rotation, as in the above mentioned differential 
micrometers. 
In the illustrated embodiment of the invention, the leadscrew or spindle 27 
has a receiving hole or bore 43 for the gearhead shaft 15 and is attached 
thereto by a set screw 44, or by an adhesive or other fastener. A retainer 
or stop element 45 is located ahead of the keyplate 35 and is retained on 
the spindle 27 by one or more set screws 46. The keyplate 35 is thus 
disposed between the gearhead 14 and stop element 45, with the stop 
element 45 being rotatable with the spindle 27. 
According to the aspect of the invention of which a preferred embodiment is 
illustrated in FIGS. 1 and 2, the linearly traveling device 34 is 
restrained against rotation at points peripherally distributed relative to 
such device, by providing at each of the points a pair of interfitting 
parts including a linear guide 38 or 39 and a member 36 or 37 guided 
thereby, and by connecting one of such interfitting parts, such as the key 
36 or 37, to the linearly traveling device 34 and maintaining the other of 
the interfitting parts, such as the keyway 38 or 39, stationary relative 
to the one interfitting part 36 or 37. 
In the illustrated preferred embodiment, interfitting parts 36 and 38 and 
37 and 39 are peripherally distributed at two points relative to the 
traveling device 34, namely, at two points diametrically opposite each 
other on the keyplate 35. In prototypes of the illustrated actuator 10, 
this feature enabled a quadrupling of the thrust of the actuator at the 
spindle 27 relative to actuators with a single key and keyway. As seen in 
FIGS. 1 and 2, the two keys 36 and 37 and the keyplate 35 are provided as 
or are in one solid unit. 
In this manner, the keys and keyways are capable of absorbing 
motor-generated side loads, keeping them away from the spindle mechanism. 
In the illustrated preferred embodiment of the invention, the keyways 38 
and 39 are machined or otherwise provided at high precision as 
antirotation slots in the front half of the tubular housing 13. 
Each antirotation slot 38 and 39 is covered by a window 48 or 49 of molded 
clear styrene, acrylic or another suitable transparent material through 
which the tab or key 36 or 37 may be observed in its travel along the 
keyway or slot 38 or 39, and at any rest position. In this respect, each 
key 36 and 37 is provided with an indicator line 51 and 52, respectively, 
while each window 48 and 49 is provided with a linear scale. As a special 
feature of the illustrated preferred embodiment, the scale at the window 
48 thus indicates travel of the actuator 10 or spindle 27 in millimeters 
and fractions thereof, while the scale at the window 49 indicates such 
travel in inches and fractions thereof. 
It is thus seen that the preferred illustrated embodiment of the invention 
provides one of the keyways or linear guides 38 with a first scale as 
shown in FIG. 3, indicating linear travel of the actuator 10 in a first 
system of measurement, such as the metric system, with the aid of a member 
36 guided by that one linear guide 38, and further provides another of the 
keyways or linear guides 39 with a second scale, as seen, for instance, in 
FIG. 4, indicating the linear travel of the actuator 10 in a second system 
of measurement, such as the inch system, different from the first system, 
with the aid of a member 37 guided by the other linear guide 39. In 
practice, this is a great convenience, since this enables the user of the 
actuator to operate in different systems of measurements without the need 
for metric or other conversion. 
The electric motor 12 preferably is of a permanent magnetic field or other 
type that reverses its direction of rotation upon reversal of polarity at 
the motor terminals 16 and 17. Accordingly, if the motor is energized 
through the jack 21 with an electric current of a first polarity, it 
rotates the gear output shaft 15 and thereby the spindle 27 in a first 
direction so that the motor 12, gearhead 14, keyplate 35, stop element 45 
and spindle 27 travel to the left as seen in FIG. 1, while the rotating 
spindle 27 threads itself through the front piece 31. The spindle 27 is 
thus thrust out of the front piece 31 as seen in FIG. 3. 
The spindle 27 is thus able to actuate any desired instrument or part. By 
way of example, FIG. 1 shows in dotted outline and on a reduced scale a 
carriage structure 54 including a base 55 and a carriage 56 slidable 
relative thereto. The front piece 31 of the actuator 10 extends through a 
bracket 57 of the base, and is mounted thereon with the aid of a nut 58 
meshing with a threaded end of the front piece 31. The carriage 56 has a 
rigid arm 59 which is engaged by the spindle 27 or by a special tip 61 
thereof. If desired or necessary, the carriage 56 may be biased into or 
toward the base 55 by a spring or other suitable device (not shown). 
By way of example, the carriage 56 may be the carrier of an optical 
component, such as a lens or mirror in a holographic or other laser beam 
utilization system (not shown). In that case, the base 55 may be attached 
to an optical table or other rigid reference surface (not shown). In such 
and similar scientific or high-technology work, adjustment resolutions in 
the micron and sub-micron range are now frequently a necessity. 
In practice, this need is often coupled with a requirement that the 
achievable travel of the adjustment be some ten to hundred thousand times 
larger than the required resolution. 
The subject invention enables these requirements to be met in an 
electrically controlled manner with electrically driven actuators. 
The main advantage of the tip 61 is the facility of providing a hardened 
metallic or other special surface for pushing against a surface of a 
carriage arm 59 or other part to be actuated. In the illustrated preferred 
embodiment, the tip 61 has a concave configuration. The convex tip 61 
provides practically a single point contact with the part to be acuated. 
In practice, the shape of the tip 61 can be varied to accommodate various 
contact configurations. By way of example, the tip 61 may be provided with 
a conical configuration, as indicated in FIG. 3 in dotted outline 63, in 
order to fit a "V-groove" in a part to be actuated. 
As the motor 12 keeps rotating in one direction, the actuator 10 eventually 
reaches its outer extreme extension, as indicated in dotted outline at 65 
in FIG. 1. At that point, the keyplate 35 and the stop element 45 also 
reach their extreme outward limit of travel, indicated in dotted outline 
at 66 in FIG. 1. The element 45 may be designed as a stop engaging the 
inside of the front piece 31, thereby preventing further linear outward 
travel of the spindle 27. The stop element 45 may be made of metal or, if 
desired, of plastic in order to cushion the stopping function. The 
keyplate 35 may also be a molded plastic part. 
The tip 61 may be in the form of a screw threaded into an internally 
threaded axial front bore 68 of the threaded spindle 27. The head of the 
tip 61 may have a larger diameter or dimension than the diameter of the 
spindle 27, so as to provide for a stop limiting retraction of the spindle 
27 into the front piece 31 of the actuator. A washer 69 of Teflon or 
another sturdy cushioning material may be provided between the spindle 27 
and the head of the tip 61, in order to cushion and absorb any thrust and 
shock of the retracting spindle 27 running into its limit. 
In order to avoid pinching of the cable 25 between the housing 13 and motor 
12 during travel thereof, a disc (not shown) may be attached to the rear 
end of the motor 12 at terminals 16 and 17 so as to close the annular gap 
between the motor 12 and housing 13 and wipe along the inside of the 
housing 13 during travel of the motor. 
The linear actuator shown in FIGS. 1 to 4 may be energized in any desired 
manner, such as by application of a controlled electric current through 
the jack 21 to the electric motor 12. Limit switches (not shown) or 
equivalents thereof may be employed to stop the motor 12 upon the stop 
elements 45 and 61 or 69 reaching their limits. 
The subject invention and its embodiments meet the initially stated needs 
and objectives and overcome the initially stated disadvantages. 
The subject extensive disclosure will render apparent and suggest to those 
skilled in the art various modifications and variations within the spirit 
and scope of the subject invention.