United States Patent (19) 11 Patent Number: 4,938,087

Ragard 45 Date of Patent: Jul. 3, 1990

(54) AERO BACKLASH POSITONING SYSTEM 4,753,119 6/1988 Kuspert .............................. 74/89.21
FOR AMOVABLE LINEAR AXIS FOREIGN PATENT DOCUMENTS
75 Inventor: Phillip A. Ragard, Binghamton, N.Y. 160923 11/1985 European Pat. Off. ........... 74/89.21
73 Assignee: Universal Instruments Corporation, 291.0373 9/1980 Fed. Rep. of Germany ... 74/89.21
Binghamton, N.Y. Primary Examiner-Allan D. Herrmann
(21) Appl. No.: 359,325 Attorney, Agent, or Firm-Fidelman & Wolffe
22) Filed: May 31, 1989 57 ABSTRACT
(51) Int. C. ...................... F16H 19/06; F16H55/28; A linear axis (cantilevered beam) is longitudinally dis
B25J 5/02 placeable relative to its support which, in turn, is dis
52 U.S. C. .................................... 74/89.21; 33/1 M: placeable laterally along an overhead frame so as to
74/422; 41.4/749; 901/16; 901/21; 475/183 provide X-Y positioning for pick and place spindles and
(58) Field of Search ............... 33/1 M 74/89.2, 89.21, similar tools which are attached to the beam. A particu
74/89.22, 422,798; 414/749,901/16, 17, 21; lar structural combination for accomplishing this in
248/661; 269/73 volves a low inertia servomotor driving a speed reducer
which, in turn, directly drives a short endless timing
(56) References Cited belt which, in turn, intermeshes with and drives a
U.S. PATENT DOCUMENTS toothed rack in order to provide reliable, with zero
backlash, high accuracy X-Y positioning of the tools.
2,344,078 3/1944 Brissonnet et al. ...... 888 74/798
Features of the structural arrangement allow the use of
2,484,605 10/1949 Boucher............... a 74/798
component parts requiring much less precision, and
3,060,767 10/1962 Parrett ..... as as a s 74/798
thus much less cost, of manufacture than prior art, zero
3,850,043 11/1974 Tarbox..... ... 33/1 MX
4,229,136 10/1980 Panissidi ...... ... 901/16 X backlash, linear axis positioning systems.
4,274,801 6/1981 Herb et al. ....... ... 414/749 X
4,721,005 1/1988 Yoshiji et al. .................... 901/16 X 6 Claims, 6 Drawing Sheets
s
U.S. Patent Jul. 3, 1990 Sheet 1 of 6
4,938,087
Sy
U.S. Patent Jul. 3, 1990 Sheet 2 of 6 4,938,087
A2%-2

= s = ===s== iss-s-s-s- = E ===

H II-H IA-II H

HA
SN
III
21 SNS
it.2
16
U.S. Patent Jul. 3, 1990 Sheet 3 of 6 4,938,087

N
N
e N

2ZZZZ2
%
s
N
S
II, II
2NNYX, IN
t
U.S. Patent Jul. 3, 1990 Sheet 4 of 6 4,938,087

SNSS
21 N

Allel
e s
NNNNNN
U.S. Patent Jul. 3, 1990 Sheet 5 of 6 4,938,087
U.S. Patent Jul. 3, 1990 Sheet 6 of 6 4,938,087

NS
% 3. y
1. 23 N
3.Né N<2
ef, S. 6
N33.12
NZ
64 22
 4,938,087
1. 2
Features of the structural arrangement allow the use of
ZERO BACKLASH POSITONING SYSTEM FOR A component parts requiring much less precision, and
MOVABLE LINEAR AXIS thus much less cost, of manufacture than prior art, Zero
backlash, linear axis positioning systems.
BACKGROUND AND SUMMARY OF THE
INVENTION BRIEF DESCRIPTION OF THE DRAWINGS
The invention is in the particular field of equipment FIG. 1 is a perspective of a machine incorporating
for transferring electrical components to printed circuit the instant invention.
boards automatedly for assembly therewith. However, FIG. 2 is a partial front elevation of one of the canti
O levered beams of FIG. 1.
it is contemplated that the structure is readily adaptable
to other electrical component handling equipment and FIG. 3 is a cross section, as viewed generally in the
to similar robotic applications of a more general nature. direction of arrows 3-3 of FIG. 2.
Such transferring generally involves cyclical moving FIG. 4 a top plan view of FIG. 3.
of a pick and place head such as a vacuum spindle from 15
FIG. 5 a bottom plan view of the device of FIG. 3.
a "picking” station at which an electrical component is FIG. 6 a plan view of the inside of the speed reducing
picked up to a "placing' station at which the compo unit.
nent is placed down at a selected location on the face of FIG. 7 a cross section, as viewed generally in the
the circuit board. The X-Y positioning of the selected direction of arrows 7-7 of FIG. 6.
circuit board location relative to the vacuum spindle is DETALED DESCRIPTION OF THE
accomplished by moving either the circuit board or the 20 INVENTION
spindle in X and Y, or moving both in at least one of the
directions. Referring to FIG. 1, circuit boards (not shown) are
Devices for repositioning the pick and place head in fed along feed supports 92 for population with electrical
X and Y with the speed, accuracy, reliability, and re components by means of pick and place spindles 90.
peatability required by the industry have involved 25 Spindles 90 are attached to a cantilevered arm (linear
mounting the head for movement along and on preci axis) which is displaceable (in the direction of the ar
sion ground ways (in the X direction), which are sup rows thereon) and, in turn, is supported by a support
ported at each end for movement perpendicular thereto member 40 which is laterally displaceable along over
(in the Y direction), with these movements being along head frame 10 in the direction of the arrows indicated
the axes of precision ground leadscrews (defining theX on support member 40. Thus, a pick and place head 90
and Y axes) via mating ball nuts. Inherent to these de is X-Y positionable in order to retrieve components
vices are the complicated and costly drive mechanisms from a pick-up station and place them at a selected
necessary to accomplish the linear travel of an axis with location on a circuit board, under the command of a
the precision required. controller 36.
It is also known in the prior art to use harmonic drive 35 Various forms of electrical component supplies may
gearing for a reducing unit in precision X-Y positioning be utilized for the machine, such as the reels of taped
systems. However, such units are limited to an input of components 32 and the sticks of components which are
only about 2000 rpm and can provide a low end reduc mounted on a turret at 34. Additionally, vibratory com
tion ratio of only about 50:1. These limits compare unfa ponent feeders (not shown) may be used for component
vorably to a prototype of the instant invention which 40 supply.
accepted an input of 4800 rpm and provided the low
end reduction ratios of 10:1-15:1 which are desirable for Turning to FIGS. 3 and 4, support 40 is suspended
servos. Further, the higherinertia of the harmonic drive from frame 10 by means of front rails 14 and rear rail 12
unit causes more energy to be consumed in the power which define the X axis movement of support 40 and,
train. The necessary reduction would be very difficult 45 hence, arm 80. A toothed rack 18 is hinged to the frame
to achieve with the harmonic drive and, if achievable, 10 athinge 20, and a spring loading mechanism 22 biases
would be much more expensive than that of the instant rack 18 into engagement with the timing belt 54. Thus,
invention. should guide rails 12 and 14 and their respective wheel
Thus, it is an object of the invention to provide reli bearings 46 and roller bearing 44 allow for travel which
able, high accuracy X-Y positioning of a moveable SO is not exactly parallel with the rack 18 over the func
linear axis without the need for the precision required of tional length thereof, the spring biasing of the rack 18
the component parts of prior art devices. This and other into engagement with timing belt 54 will maintain
objects of the invention will become more apparent proper engagement of the teeth of belt 54 and rack 18
from the following detailed description, drawings, and and thus maintain constant torque on the speed reduc
claims of the invention. 55 tion unit 51 and the servomotor 50. Frame 10 also has an
encoding bar 76 extending along the length of front rails
BRIEF SUMMARY OF THE INVENTION 14; and support member 40 contains a reader 74 for
A linear axis (cantilevered bean) is longitudinally monitoring bar 76 and thus the position of support 40 as
displaceable relative to its support which, in turn, is it traverses frame 10.
displaceable laterally along an overhead frame so as to Referring to FIG. 4, the spring loading mechanism 22
provide X-Y positioning for pick and place spindles and comprises arms 24 pivotal about points 26 and having
similar tools which are attached to the beam. A particu wheel bearings at the ends distal from pivot points 26,
lar structural combination for accomplishing this in with a spring 30 in tension between the pivotal arms 24
volves a low inertia servomotor driving a speed reducer so as to bias them into engagement with rack 18.
which, in turn, directly drives a short endless timing 65 A tachometer 48 facilitates rate control in accordance
belt which, in turn, intermeshes with and drives a with controller 36 (FIG. 1).
toothed rack in order to provide reliable, with zero Referring to FIGS. 6 and 7, the speed reduction unit
backlash, high accuracy X-Y positioning of the tools. 51 comprises three wheel bearings 62 attached by means
 4,938,087
3 4.
of pins 70 to lateral arms 66 of an output shaft 64. Lat It is also to be understood that the following claims
eral arms 66 have reduced portions 68 (FIG. 6) so that are intended to cover all of the generic and specific
arms 66 may flex generally radially of a drive pin 52 of features of the invention herein described, and all state
motor 50 so as to maintain a force at the point of tan ments of the scope of the invention which, as a matter of
gency of each wheel bearing 62 with the centrally ar language, might be said to fall therebetween.
ranged drive pin 52, with this force being sufficient for Now that the invention has been described, we claim:
rotating output shaft 64 in concert with drive pin 52 1. An apparatus for providing precision linear dis
without relative slipping therebetween. A flexible ring placement of an axis relative to a support, and compris
58 surrounds the triad of wheel bearings 62 and is pre ing in combination:
vented from rotating relative to housing 56 by means of 10 a drive mechanism having a servomotor attached to
pin 60 (FIG. 6). Although not indicated in the drawings, and moveable with one of said axis and said sup
the internal diameter of flexible ring 58 is sufficiently port, and a rack attached to and moveable with the
less than that of a circle containing the locus of outer other of said axis and said support, said rack being
points of tangency of wheel bearings 62. Thus, flexible 15 attached hingedly so as to be pivotal about a pivot
ring 58 is distorted somewhat triangularly in shapeso as axis which is parallel longitudinally to said rack;
to preload the wheel bearings 62 into engagement with a speed reducer operatively associated with said ser
drive pin 52. vomotor and providing direct drive to a timing
As seen in FIGS. 4 and 7, the smooth side of timing belt;
belt 54 is wrapped around a pulley 72, which is attached 20 said timing belt intermeshing with said rack such that
to output shaft 64, and a tensioning pulley 73 so as to forward and reverse rotation of said motor pro
present a generally straight portion of timing belt 54 for vides to and fro relative linear motion, respec
intermeshing engagement with rack 18 (FIG. 4). tively, between said axis and said support so as to
The description so far has dealt with the drive for displace said axis linearly along a Y coordinate and
moving a support 40 in the X direction as indicated in 25 longitudinally of said rack; and
FIGS. 4 and 5. A similar drive mechanism is provided means for biasing said rack about said pivot axis
for movement of the arm 80 in the Y direction orthoga toward said timing belt in order to maintain contact
nal to support member 40. This second drive mecha between teeth of said rack and said belt.
nism is generally indicated at 78 in the drawings and, as 2. An apparatus as in claim 1, wherein said drive
seen in FIG. 2, the hinged rack 82 is attached to arm 80 mechanism comprises a first drive mechanism, and fur
for movement therewith. ther comprising:
FIG. 5 illustrates an alternative endless belt arrange a frame; and
ment for transferring drive from the speed reduction a second drive mechanism similar to said first drive
unit to the hinged rack 82, although the same structure mechanism and operatively associated with said
as illustrated in FIG. 4 could be utilized here also. As 35 support and said frame so as to provide relative
seen in FIG. 5, astructural arrangement is provided that movement therebetween and linear displacement
allows a pinion gear 72 to engage the toothed outer of said axis relative to said frane and along an X
portion of timing belt 54 (as opposed to the pulley 72 of coordinate orthoganal to said Y coordinate.
FIG. 4 engaging the untoothed, inner side of timing belt 3. An apparatus as if claim 2, and further comprising:
54). It is contemplated also that the timing belt 54 of 40 a beams suspended and cantilevered from said sup
FIG. 4 could be toothed on both sides such that pinion port and containing said axis.
gears may be used in place of members 72 and 73 of 4. An apparatus for providing precision linear dis
FG, 4. placement of an axis relative to a support, and compris
Thus, the drive mechanism of the instant invention ing in combination:
provides zero backlash for moving linear axes much less 45 a drive mechanism having a servomotor attached to
expensively than that provided by the prior art devices. and moveable with one of said axis and said sup
In a prototype of the invention, the Universal Instru port, and a rack attached to and moveable with the
ments Corporation VME controller having part code other of said axis and said support;
8224A was used. Also, the high stiffness-to-weight ratio a speed reducer operatively associated with said ser
required of the cantilevered beam 80 demands a rather vomotor and providing direct drive to a timing
critical material composition of the beam, and the pro belt, said speed reducer comprising an output shaft
totype used a carbon fiber material like that manufac being concentric with a drive pin of said servomo
tured by Union Carbide and comprising unidirection tor along a centerline, said output shaft having
ally layed up carbon fabric. arms extending laterally of said centerline, with
Another advantage of the inventive structure over 55 each of said arms supporting a bearing in frictional
the prior art is the ease with which support 40 is assem engagement with said drive pin at a point of tan
bled with and disassembled from frame 10, and the gency between said drive pin and each bearing,
frontmost rail 14 is easily bolted to or unbolted from said speed reducer further comprising means for
frame 10 in order to attach or release support 40. maintaining a force between said drive pin and
Having described the invention, it will be seen that each bearing at said tangency point sufficient to
the objects set forth above and made apparent from the ensure rotation of said output shaft in concert with
preceding description are efficiently obtained and, since rotation of said drive pin and
certain changes may be made in carrying out the above said timing belt intermeshing with said rack such that
method and in the construction set forth without de forward and reverse rotation of said motor pro
parting from the scope of the invention it is intended 65 vides to and fro relative hinear motion, respec
that all matter contained in the above description or tively, between said axis and said support so as to
shown in the accompanying drawings shall be inter displace said axis hinearly along a Y coordinate and
preted as illustrative and not in a limiting sense. longitudinally of said rack.
 4,938,087
5 6
6. An apparatus as in claim 4, wherein said force
An apparatus as in claim 4, wherein said force maintaining means comprises:
maintaining means comprises: a flexible ring surrounding said bearings and engaging
each said bearing along a portion of a periphery
a reduced portion of each said laterally extending arm 5 thereof, said ring being fixed against rotation rela
such that each bearing is biased into engagement tive to a housing of said speed reducer and having
an inner diameter less than a circle locus surround
with said drive pin by flexure of the corresponding ing and tangent to each of said bearings.
arm at said reduced portion.
10

15

20

25

30

35

45

50

55

65