Positioning systems

An x-y positioning device in which a cable or chain is used to drive a carriage, powered by two motors. The same cable that moves the carriage also constrains the angular orientation of the moving mechanism. In so doing, the moving parts can be made lighter and less expensively, while providing improved dynamics. All is advantageously applied to large, flat-bed plotters, to a computerized engraver, to a large sign painter, or to an elevator.

The present invention relates generally to new and useful improvements and 
structural refinements in motive power systems involving computerized 
drive mechanisms having general utility in the arts, and more particularly 
aims to provide improvements in the means for driving a carrier via 
fixed-position driving motors, the motion being transmitted via a chain. 
The invention, in broader aspects, may be embodied in any device embodying 
a positioning system in two dimensions known as a rectangular drive or X-Y 
drive device. 
In what are believed to be new and novel practical applications, the 
elucidated concept has been embodied into a practical use for 
accomplishing certain functions in a new and novel way and 
exemplifications are herein given showing the movement of an engraving 
tool relative to a workpiece, the movement of a plotter over a planar 
surface, the movement of a sign painting mechanism over a 
vertically-disposed surface, and the movement of an elevator car relative 
to a vertical wall of a housing such as an office building, hotel or the 
like, the wall containing a plurality of doors leading thereinto. 
Admittedly, the idea of following in mutually orthogonal directions via a 
computer-operated mechanism is not new. Likewise it is to be admitted that 
per se cable-driven plotters and computer-controlled engravers are not 
new. 
Without intending to place undue limitations upon the scope of the 
invention, beyond what may be required by the state of the prior art, the 
particular embodiments may be briefly defined as each embracing the 
concept of a positioning system involving a rectangular or X-Y drive where 
a pair of driving motors have a capacity for moving a carrier in arbitrary 
motions over a defined area. Desirably, such device would be 
computer-controlled. 
The driving motors function separately or unisonly through appropriate 
trains to drive the carrier over a planar area. 
Rotation of either motor alone will be seen to move the carrier diagonally. 
The desired positioning is normally attained by the simultaneous rotation 
of both motors. 
We provide a positioning system of the above-defined character in which 
ruggedness and durability of construction are combined with simplicity and 
ease of use and protection against usual but hard conditions of practical 
use resulting in an apparatus which effectively meets the normal 
requirements therefor and performs its functions in a practical and 
dependable manner. 
Further, while the components are uniquely compact, they are nevertheless 
readily accessible for repair and replacement purposes with a consequent 
reduction in maintenance costs over related devices heretofore known. 
Other objects and purposes hereof are to provide advantageous structural 
and operational features in devices of the class to which reference has 
been made so as to offer an apparatus having the following inherent 
meritorious characteristics: first, engineeringwise, a low cost in 
production and uniqueness in design of coacting parts wherefor the 
components are coordinated for facile assembly; second, a susceptibility 
to easy installation, third; a high degree of efficiency and dependability 
in its operational use; fourth, the securement of a higher degree of 
accuracy and greater degree of variety in the manner of work performed 
therewith than has heretofore been possible with prior devices known in 
the art; fifth, the attainment of a convenience of arrangement of parts 
and a flexibility or a capability of adjustment by which a variety of work 
can be produced by means of the same device; and sixth, the provision of 
such other improvements in and relating to positioning systems of the type 
above referred to as are hereinafter described and claimed. 
The invention delineates a rectangular drive system with the significant 
characteristic that the ultimate positional accuracy of the driven member 
is maintained while using small and lightweight first and second 
carriages. The motion of the driven member or carrier is provided by a 
chain which is motivated by motors fixedly mounted on a base. The chain is 
attached directly to the driven member, eliminating the possibility of 
lost motion between the motor drivers and the driven member. 
The chain travels over fixed pulleys mounted on the base and over movable 
pulleys mounted on the carriages. 
The stringing of the chain is such that the angular orientation of the 
first carriage is maintained entirely by the chain and not at all by its 
constraining guide rail. It is this feature which makes possible a 
mechanism lightweight, and compact in size and low in cost of production. 
To make relatively large versions of the system, it is only necessary to 
increase the lengths of the chain and guide rails. Although the chain and 
guide rails would need to grow in sizes in order to maintain the necessary 
rigidity over larger spans, the cost and weight penalties would be slight 
as compared to those in the cases of known prior designs. 
Since the positional accuracy of the driven member is ultimately determined 
by relative motions between the operating members, closely fit rigid 
structures are dictated while still allowing smooth and free motions 
between the components. 
The motion of the driven element is constrained in one direction by a 
stationary structure in the form of a rigid bar or guide rail. The 
mechanism used to drive the driven element in a direction parallel to the 
guide rail is mounted on the stationary base. Size, weight and location 
being relatively unimportant, good positional accuracy, repeatability and 
rigidity are readily realized. 
Although the employment of a pair of straight guide rails hinged and one 
being pivotable relative to the other is dictated, the positional accuracy 
is actually determined by the chain. That is, no fixed angle is required 
to be structurally maintained by the guide rails. 
Further objects are to provide a positioning system conformable to the 
desiderata of the preceding paragraphs and offering specific improvements 
in its various operating instrumentalities, which themselves are minimum 
in number, wherefor it is simple and compact in accordance with the 
demands and desires of manufacturers and customers alike and so as to 
provide distinct advantages in that it is practical in value, durable in 
organization, reliable in operation, and efficient in use. 
These foregoing objects and other incidental ends and advantages 
characterize the device of the invention, and distinguish it from 
previously known devices of a kindred nature. 
Although the law requires a full and exact description of at least one form 
of the invention, and several follow, it is, of course, the purpose of the 
patent to cover the inventive concept therein no matter how it may later 
be disguised by variations in form; and the appended claims are intended 
to accomplish such purpose by particularly pointing out the combinations 
in which the inventive concept may be found. 
The invention possesses other objects and features of advantage, some of 
which, with the foregoing, will be set forth in the following description 
of our invention. We do not limit ourselves to this disclosure of species 
as we may subsequently adopt variant embodiments thereof within the scope 
of the claims.

Reference is first made to the basic concept as dramatized in the 
simplified FIG. 1 showing. 
Here are shown a pair of fixed-position drive motors 10 and 12 fixed on a 
base A, a sequential series of pulleys 20, 22, 24, 26, 28, 30, 32 and 34, 
a fixed guide rail 40, a movable guide rail 42 normally 
perpendicularly-disposed as to guide rail 40 but pivotable relative 
thereto by means of a pivot or hinged joint 44, a pair of spaced carriages 
50 and 52, a carriage 50 mounting pulleys 24 and 26 and being movable 
along fixed guide rail 40, carriage 52, mounting pulleys 32 and 34 and 
being fastened to the end of movable guide rail 42, and a carrier 70 
slidably mounted on movable guide rail 42. Pulleys 20 and 22 are mounted 
on base A. 
A chain will be considered to consist of two parts, namely part 80, 
represented by solid lines, and part 82, represented by dash lines which 
chain is entrained in turn about the freely rotatable drive pulleys of the 
drive motors and the pulleys as will be described for driving and 
orienting carrier 70. 
In following the chain train, one terminus of chain part 80 is seen to be 
fixed to a post 84 on carrier 70 and is entrained over pulleys 26 and 22, 
thence over the drive pulley of drive motor 10, and thence is entrained 
over pulleys 28 and 32 before return to the carrier where it is looped 
over a retainer 86, then passing outwardly from the carrier as chain part 
82 for passage over pulleys 34 and 30, thence over the drive pulley of 
drive motor 12, and thence over pulleys 20 and 24 before return to the 
carrier when the opposite terminus is fixed to a post 88. 
It is best to consider each chain part 80, 82 separately or individually in 
order to appreciate more readily the capability of the chain parts to 
orient carrier 70 and hold same in desired orientation. 
Assume first a rotative motion in drive motor 10, in a counterclockwise 
direction as viewed in FIG. 1, and assume further for the moment that 
drive motor 12 is non-rotative. The motion of carrier 70 will be upward 
and rightward, again as viewed in FIG. 1. 
Clockwise rotation of drive motor 10, still with drive motor 12 remaining 
idle, will see the motion of the carrier as being downward and leftward. 
In a symmetrical way, if drive motor 12 rotates while drive motor 10 is 
non-rotative, the carrier is otherwise driven. Counter clockwise rotation 
of drive motor 12 causes the carrier to move downward and rightward 
whereas clockwise rotation causes movement upward and leftward. 
By combining and controlling the relative rotations of motors 10 and 12, 
obviously any desired motion of the carrier is achievable. 
In every case, the resultant motion is caused by the responsiveness of one 
of the chain parts to the movement of the other of the chain parts. 
With no initial slack in chain part 80, its tensioning will not change when 
carriage 70 is moved in translation. Too, it will not offer any 
interference to the clockwise rotation of the carriage assembly around 
pivot 44, although counterclockwise rotation of the assembly around the 
pivot would be precluded by chain part 80. Similarly, chain part 82 would 
offer no interference with any translation of the carriage assembly but 
would prevent any clockwise rotation of the carriage assembly around pivot 
44, although counterclockwise rotation around the pivot would be allowed. 
Combining the effect of both chain parts, the carriage assembly is free to 
translate but is rigidly held in angular orientation. Retainer 86 holds 
the ends of the chain parts thereby establishing their lengths and by 
moving within this retainer one chain part is lengthened while the other 
is shortened, thereby changing the angular orientation of the carriage 
assembly. 
It should be incidentally noted that if carrier 70 were moved along movable 
guide rail 42, the chain parts would move over their pulleys, but would 
not interfere with the motion. 
Again, to illustrate the motion of carrier 70, let drive motor 10 rotate in 
the clockwise direction while drive motor 12 holds chain part 82 still at 
the motor. As drive motor 10 rotates clockwise, chain part 80 is drawn 
from pulleys 28 and 32 and released to pulleys 22 and 26. The chain motion 
described would tend to move carrier 70 down and move the carriage 
assembly to the left or to move the carriage assembly and the carrier. 
However, either motion would cause chain part 82 to move. 
If the carrier were to move down while the carriage assembly did not 
translate, chain part 82 would have to move the drive pulley at drive 
motor 12 in counter clockwise direction. On the other hand, if the 
carriage assembly were to move to the left without the carrier moving 
down, chain part 82 would cause the drive pulley at drive motor 12 to 
rotate in clockwise direction. 
Since motor 12 is not rotative in this example, the motion of the carriage 
assembly and the carrier must have equal motions to the left and down when 
the drive motor 10 rotates in clockwise direction. If drive motor 10 is 
rotated in the counter clockwise direction with drive motor 12 
non-rotative, the motion of the carrier would be up and to the right. 
Contrariwise, if drive motor 12 rotates while drive motor 10 is not 
rotating, the carrier is driven in other directions. Counter clockwise 
rotation of drive motor 12 causes the carrier to move down and to the 
right whereas clockwise rotation causes rotation up and to the left. 
As aforesaid, by combining the rotations of drive motors 10 and 12, any 
motion of the carrier is possible. 
Reference is now made to FIGS. 2-7, same representing an exemplification of 
an engraver with the drive mechanism being exploited to drive a diamond 
stylus to a correct position relative to a workpiece combined with a means 
for effecting movement of the stylus on command, lowering it into or 
raising it from the engraving position. 
Computer 211 is associated with the actuating mechanism mounted on the 
engraving work table indicated by 213. 
The drive mechanism is used as a component of an automated designing system 
in combination with the computer, the system envisioning the conversion of 
data of a plot plan to algorithmic form acceptable to the computer, which 
data is oriented within the computer memory and is then converted from the 
computer memory to a visibly useful form. 
The actuating mechanism envisions generally an electric stepper motor 229, 
a bowden wire 249 for transferring motion and force from the motor 
assembly to an inscribing stylus 215, a pair of spring means 247 and 267 
for pressing the stylus against workpiece W, and a potentiometer 225 for 
sensing or locating the workpiece surface and for calibrating the spring 
force. 
Conceptually, the system functions thus: when it is desired to move stylus 
215 into the engrave position, computer 211 moves stepping motor 229 
counterclockwise. The stylus, being initially free, is driven toward the 
work through bowden wire 249 and the pair of cooperant springs, with 
little length change actuate a potentiometer 225 moving at approximately 
the same rate as the drive chain of the mechanism. 
Stylus 215 is movable over the work table by the drive mechanism and 
operationally is driven to the engrave position over workpiece W fixed by 
the usual mounting means (not shown) supported upwardly of the work table. 
Initially, the stylus is free, that is, in withdrawn upward position, as it 
is driven to the desired position over the workpiece. 
Once in position, the stylus is motivated toward the work through actuation 
of the bowden cable, its spring steel wire being enclosed within a casing 
251 and functioning for transmitting a longitudinal motion, especially 
around a curve to a point at a distance from where the motion is initiated 
and around the curvature in the cable and casing, the same lending 
themselves to such ready manipulation, as is known. 
To move stylus 215 to its operating position, computer 211 will move a 
stepping motor 229 counterclockwise. 
The stylus actuating mechanism is enclosed within a housing comprised of a 
mounting plate 221 and a cover 223. 
Potentiometer 225 is enclosed within the housing, being mounted relative to 
mounting plate 221 by means of mounting clips 227. 
Stepping motor 229 is mounted on mounting plate 221 externally of the 
housing, which motor mounts a drive shaft 231 supporting a drive sprocket 
233 around which the lower reaches of bead chains 235 and 237 are 
entrained. 
Vertically above and spaced from drive sprocket 233 are a pair of coaxially 
aligned pulleys 239 mounted on a pulley spacer so as to be spaced from 
each other and around each of which pulleys the upper reach of a bead 
chain is entrained. 
The free ends of the bead chains are then extended downwardly to the 
opposite sides of spaced spring spacers 241 and held fixed as to each 
other by a screw 243 and nut 245. 
An extension spring 247 is fixed at its lower extremity to screw 243 
between spring spacers 241 and at its upper extremity to the inboard 
terminus of bowden wire 249 sleeved in casing 251, the casing being held 
relative to the housing by a cable sleeve anchor 253 and a set screw 
radially extended thereinto. 
The lower extremity of cable sleeve anchor 253 sleeves a stop bumper 255 
through which the bowden wire extends and is receivable in a crimp-ring 
terminal, which terminal is held by a screw and nut assembly 259 which 
also mounts the upper terminus of extension spring 247. 
The opposite extremity of the bowden cable extends through a cable guide 
263, the lower end of which cable guide is sleeved in and held by a cable 
guide base 265. 
A compression spring 267 is sleeved around the bowden cable and within the 
cable guide, seating between the end of the bowden cable casing and the 
cable guide base. 
The bowden cable terminates and is connected to a terminal crimp ring 269 
which supports a downwardly-depending anchor cable 271. 
Potentiometer 225 is connected to extension spring 247 by a crimp ring 273, 
which crimp ring is fixed to the extension spring and is slidable relative 
to the potentiometer. 
As the stylus contacts the work surface, its downward vertical motion is 
stopped. Subsequent movement of the chain driven by the stepping motor is 
absorbed by the springs. 
As spring 267 is compressed, it develops a force which is applied through 
its linkage to the stylus. The force exerted by spring 247 is the same as 
the force exerted by spring 267. 
The force in spring 247 is present only after spring 247 has been extended 
by the motion of the chain. 
During the initial motion, spring 247 does not lengthen and the 
potentiometer motion is nearly the same as the chain motion. 
The computer, sensing the chain movement responsive to the commands of the 
stepping motor, knows how far the potentiometer must move if spring 247 is 
to stay at a constant length. 
The difference between the expected motion of the potentiometer with the 
constant length of spring 247 and the measured motion of the potentiometer 
is a measure of the extension of spring 247 and accordingly the force in 
the stylus. 
With reference to FIG. 7, the computer algorithm determines when the force 
at the stylus is equal to the requested value tests for a greater or equal 
value of the difference between the stepping motor motion and the 
potentiometer motion. This criterion is shown graphically. Same is shown 
as somewhat idealized as deviations resultant from friction are not here 
taken into account. 
Per the plane cartesian coordinate system where the abscissa represents the 
extent of chain motion and the ordinate represents the extent of 
potentiometer motion, the coordinates are representative of three 
typically requested forces, namely 1 pound, 2 pound and 3 pound. 
Illustratively, imagine the requested force to be 3 pounds. Computer 
detection would operate to stop the chain motion when the algorithm sensed 
the crossing of the 3 pound line. 
As the stylus contacts the work surface, it stops its vertical motion. 
Subsequent movement of the chain driven by the stepping motor is absorbed 
by the two springs. As one spring is compressed, it develops a force which 
is applied through its linkage to the stylus. Except for certain 
frictional losses in the bowden cable, the force exerted by the other 
spring is the same as the force by the first spring. This force in the 
second spring is present only after the spring has been extended by the 
motion of the chain. 
During the initial motion, the second spring essentially does not lengthen 
and the potentiometer motion is nearly the same as the chain motion. The 
computer knows how far the chain moves in response to the commands to the 
stepping motor, so that it knows how far the potentiometer must move if 
the second spring is to stay at constant length. The difference between 
the expected motion of the potentiometer with the constant length of the 
second spring and the measured motion of the potentiometer is a measure of 
the extension of the second spring and therefore the force in the stylus. 
If the problem of raising and lowering the stylus were straightforward, 
that is raising it to a first fixed height in the non-operating mode and 
lowering it to second fixed height in the operating mode, the matter of 
actuator design would not be too complicated. Problems are compounded 
however in the presence of curved or other non-horizontal planar surfaces 
of the work which dictate that stylus positioning adjust to and compensate 
for such irregularities. 
Reference is now made to FIGS. 8-14, same representing an exemplification 
of an X-Y plotter over a planar surface for a graphical display of data 
with the drive mechanism being exploited to drive a pen or writing stylus 
to a correct position relative to a workpiece combined with a means for 
effecting movement of the pen on command according to signals from a 
computer, lowering or enabling it into writing position and raising or 
disabling it away from writing position. 
As envisioned, the data is graphically displayed by the pen carried by the 
X-Y mechanism which may be positionable in response to a computer's 
digital signals. 
The X-Y mechanism may be used to plot a mathematical function as a series 
of straightline segments, the first of which may begin from a selected 
starting point on a writing medium such as a graph and the last of which 
may terminate at a selected finishing point. 
Conceivably, the first point to be plotted may not be coincident with the 
origin point of the X-Y coordinates, in which case the pen must be 
disabled while being moved to the first point to be plotted, and 
therefollowing the pen must be enabled and remain so enabled to draw a 
line or a series of connected line segments between successive points as 
computer dictated. 
As known, the computer may produce data representative of mathematical 
functions, for example, which may be graphically displayed by the X-Y 
plotter. 
A pen position control circuit will include digital-to-analog converter 
circuitry which controls the X and Y movements of the pen. 
The coupling between the pen position control circuitry of the computer and 
the X-Y plotter may be of conventional design, with the pen being 
conditioned in a writing mode or a monitoring mode by a pen write control 
solenoid, responsive to the computer, and mechanically coupled to the pen. 
A solenoid is in the normal energized, pen lifted and disabled position. 
The solenoid, when non-energized, will allow the pen to lower into contact 
with the paper or other writing medium on the X-Y plotter. 
The computer will produce two pen control signals which determine the 
writing status of the pen, the signals being identified as format up and 
format down logic which produce the logic signals on the solenoid in 
response to corresponding binary coded input signals from the computer, 
the two signals operating to disable or enable the pen. 
A stylus or pen 303 is releasably mounted on or held relative to a clamp 
305 by a spring 305', the clamp being fixed to a body 307 which is sleeved 
upon movable guide rail 342 so as to be swingable relative thereto 
responsively to the actuation of an actuator 311 which, as shown in FIGS. 
8 and 11, is tied to a solenoid S and is entrained over a pulley 313 
coaxial with pulley 322, over a pulley 315 coaxial with pulley 324, over a 
pulley 317 mounted on body 307, over a pulley 319 mounted on carrier 370, 
over a pulley 321, and thence outwardly therefrom over a pulley 323 
coaxial with pulley 332 with its other terminus being tied to a post 325 
mounted on base B. 
A pair of fixed-position drive motors 310 and 312 are mounted on a base B. 
Pulleys 320, 322, 324, 326, 328, 330, 332 and 334 are disposed as in the 
case of the FIG. 1 basic concept pulleys, pulleys 320 and 322 being 
mounted on base B. 
A fixed guide rail 340 is fixed relative to base B and a movable guide rail 
342 is pivotable relative thereto by means of a pivot 344. 
Spaced carriages 350 and 352 are sited on opposite sides of the base. 
Carriage 350 mounts pulleys 324 and 326 and is movable along fixed guide 
rail 340. Carriage 352 mounts pulleys 332 and 334. 
A support wheel 360 is mounted on carriage 352. 
A driven carrier 370 is movable along and relative to movable guide rail 
342. 
Chain parts 380 and 382 are entrained about the respective drive wheels of 
the drive motors and the pulleys for driving and orienting the carrier. 
Chain part 380 threads outwardly from a fixed post on carrier 370, over 
pulleys 326 and 322, over the drive wheel of drive motor 310, over pulleys 
328 and 332, and returnably to the carrier where it is looped around a 
retainer and then, as chain part 382, over pulleys 334 and 330, over the 
drive wheel of drive motor 312, over pulleys 320 and 324 and returnably to 
the carrier where the opposite terminus of the chain is fixed to a post. 
The chain parts cooperantly allow a free translation of carrier 370 while 
forcing the carrier to be held rigidly in any angular orientation and this 
is so whether one drive motor is rotating while the other drive motor is 
not rotating or both drive motors are rotating simultaneously. Whatever 
the rotation or non-rotation of the drive motors, the motion is such that 
as one chain part is driven the other chain part is driven responsively 
wherefor any desired positioning of the carrier is possible. 
Reference is now made to FIGS. 15-18, same representing an exemplifcation 
of an X-Y plotter over a vertically disposed planar surface represented by 
a wall Q of a building having a window P enclosed therewithin and a 
mechanism embodying the spirit of the invention, the drive being exploited 
to drive a paint spray device PS to a correct position relative to the 
window, it could be a billboard as easily, combined with a means for 
effecting movement of the paint spray drive on command according to 
signals from a computer, enabling it or opening it into operational mode 
for the painting position and disabling it or closing it into 
non-operational mode for the non-painting position. 
A pair of fixed position drive motors 410 and 420 are mounted on a base 
rail BR serving as the fixed guide rail. Pulleys 422, 424, 426, 428, 430, 
432, 434 are disposed as in the case of the FIG. 1 basic concept, pulleys 
420 and 422 being mounted on base rail BR, pulleys 424 and 426 being 
mounted on a carriage 450, pulleys 428 and 430 being mounted on a top 
cross rail CR, pulleys 432 and 434 being mounted on a carriage 452. 
Base rail BR serves as a fixed guide rail 440 and a movable guide rail 442 
is pivotable relative thereto by means of a pivot 414. 
Carriage 450 is movable relative to base rail BR by means of rollers 453 
which embrace the base rail on opposite side faces thereof. 
Carriage 450 mounts pulleys 424 and 426. 
Carriage 452 mounts pulleys 432 and 434 and is movable relative to top 
cross rail CR by means of rollers 455 which embrace the base rail on 
opposite side faces thereof. 
A driven carrier 470 is movable along and relative to movable guide rail 
442. 
Chain parts 480 and 482 are entrained about the respective drive wheels of 
the drive motors and the pulleys for driving and orienting the carrier. 
Chain part 480 threads outwardly from a fixed position on carrier 470 over 
pulleys 426 and 422, over the drive wheel of drive motor 410, over pulleys 
428 and 432, and returnably to the carrier where it is looped around a 
retainer and then, as chain part 482, over pulleys 434, 430 and 412, over 
drive wheel 420, over pulley 424 and returnably to the carrier where the 
opposite terminus is fixed to a post. 
The chain parts cooperantly allow a free translation of carrier 470 while 
forcing the carrier to be held rigidly in any angular orientation and this 
is so whether one drive motor is rotating while the other drive motor is 
not rotating or both motors are rotating simultaneously. 
Whatever the rotation or non-rotation of the drive motors, the motion is 
such that as one chain part is driven the other chain part is driven 
responsively wherefor any desired positioning of the carrier is possible. 
The painting device comprising the usual spray nozzle and paint and air 
lines PL and AL respectively is mounted on the carrier 470 by means of 
cradles 405 mounted on and projecting outwardly from a base plate 407, 
which base plate is fixed to carrier 470. 
The painting device is cradled relative to cradle 405 and is clamped 
relative to the base plate by a clamp 409 which may be threadedly engaged 
with the base plate so as to be manually tightenable against the painting 
device. 
Reference is now made to FIG. 19, same representing an exemplification of 
an X-Y plotter over a vertically disposed planar surface represented by a 
wall T of a building having a plurality of elevator type doors D on a 
plurality of levels, each door leading to a room of the building. 
The mechanism embodies the spirit of the invention, the drive being 
exploited to position a carrier in the form of an elevator car E to a 
desired position relative to one of the doors D on one of the levels or 
floors of the building according to signals delivered thereto. 
A pair of fixed position drive motors 510 and 512 are fixed relative to the 
building at opposite corners of the side wall. 
Pulleys 520, 522, 524, 526, 510, 512, 532 and 534 are disposed as in the 
case of the FIG. 1 basic concept. 
Pulleys 510, 512, 520 and 522 are mounted on a top rail; pulleys 524 and 
526 are mounted on a top carriage. Drive motors 528 and 530 are mounted at 
the base corners of building. Pulleys 532 and 534 are mounted on a lower 
carriage. 
A fixed guide rail 540 is fixed relative to base rail and a movable guide 
rail 542 is pivotable relative thereto by means of a pivot 544. 
Carriages 550 and 552 are spaced from each other and are disposed at the 
bottom and the top of the framing. 
Carriage 550 mounts pulleys 524 and 526 and is movable along fixed guide 
rail 540. 
Carriage 552 mounts pulleys 532 and 534. 
Chain parts 580 and 582 are entrained about the respective drive wheels of 
the drive motors and the pulleys for driving and orienting the carrier. 
Chain part 580 threads outwardly from a fixed position on carrier 470, over 
pulleys 526, 522 and 510, over the drive wheel of drive motor 528, over 
pulley 532, and returnably to the carrier where it is looped around a 
retainer and then, as chain part 582, over pulley 534, over the drive 
wheel of drive motor 530, over pulleys 512, 520 and 524 and returnably to 
the carrier where the opposite terminus is fixed to a post. 
The chain parts cooperantly allow a free translation of carrier 570 while 
forcing the carrier to be held rigidly in any angular orientation, whether 
one motor is rotative while the other is stationary or both motors are 
simultaneously rotative. 
Whatever the rotation or non-rotation of the drive motors the motion is 
such that as one chain part is driven the other chain part is driven 
responsively wherefore any desired positioning of the carrier is possible.