Controlled deceleration stopping device for robot base

A stationary robotic base carries a movable robotic platform and supports a pair of vertical striker plates spaced apart by a central, elastomeric block. The striker plates are confined within a compartment of the stationary base, and extend upward into a pathway defined by a lug depending from the moving platform. The lug contacts the top portion of a given striker plate and, as the plate is struck, it tends to pivot about its bottom edge toward the other plate, compressing the elastomeric block, while the other plate is held from moving away from the block. The assembly is bidirectional, with each striker plate being yieldable toward the other as it is encountered by the moving lug. In the event that the moving element possesses more energy than the maximum stopping energy of the elastomeric block, the first encountered striker plate will pivot to such position that the lug will overtravel the striker plate and pass over the elastomeric block until it comes to rest against the stationary, nonpivoting striker plate.

BACKGROUND OF THE INVENTION 
The invention relates generally to devices for slowing and stopping movable 
machine elements, particularly those devices which embody energy 
absorption elements. The invention is broadly applicable to movable robot 
platforms or bases, and is especially applicable to rotatable robot 
platforms having a bi-directional range of movement of less than 
360.degree.. 
Many industrial robots, including the articulated arm types and 
coordinately movable slide systems, are supported on a rotatable platform 
which, in turn, is typically journalled on a fixed robot base to provide 
the system with a rotary axis of movement. The rotatable platform is power 
driven from the fixed base and is typically positioned in response to a 
signal generated by a position sensing element such as an encoder or 
resolver affixed to the drive system. Maximum end-of-travel stops are 
provided to limit the platform travel. 
If a rotatable platform is stopped in its movement by rigid stopping 
elements, the shock may result in deleterious conditions. For example: 
workpieces may be jostled in their respective grippers; the drive train 
may be damaged; and loosening of robotic components may occur. 
Energy-absorbing snubbers and shock absorbers are well-known in machine 
fields, and a typical design involves a piston and cylinder coacting 
against a fluid interface in much the same manner as the action of an 
automobile shock absorber applied between the body and frame. Prior art 
shock absorbers have certain disadvantageous features; for example: loss 
of effectiveness due to seal wear; fluid leakage in hydraulic devices; 
linear stroke and relatively long dimensions in both pneumatic and 
hydraulic devices; certain rubber bumpers are contacted directly and tend 
to degrade quickly. Additionally, the prior art devices are generally 
unidirectional in function. 
In contrast to the prior art devices, applicant has conceived a novel 
mechanical stop device for arresting movement of a robotic platform where 
the stop embodies shock-absorbing and controlled deceleration 
characteristics and, secondarily, provides for stopping of overtravel in 
the event of rapid degradation of the cushion element. The stop is also 
configured to act against bi-directional rotary movement. 
It is therefore an object of the present invention to provide a compact, 
simplified, cushioned stop for a movable robotic platform. 
Another object of the present invention is to provide a mechanical 
cushioned stop for a robotic platform which is relatively trouble-free and 
maintenance-free. 
A further object of the invention is to provide a mechanical robotic 
platform stop having controlled deceleration characteristics. 
SUMMARY OF THE INVENTION 
The invention is shown embodied in a robot having a (relatively) stationary 
base and a moving platform, where the improved means for stopping the 
moving member comprises a lug affixed to, and extending downward from, the 
moving member, and where the lug moves along a defined lug path. An 
elastomeric block is supported on the stationary base and is backed up by 
a relatively fixed base-carried element. A striker plate is supported in a 
generally vertical attitude along a bottom edge adjacent to the 
elastomeric block and extends upward into the lug path. The striker plate 
is contacted by the moving lug near its topmost edge so that the striker 
plate will tip about its supported edge when contacted by said lug, and 
thereby compress the elastomeric block, effecting slowing and stopping of 
the moving member.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 of the drawings depicts an industrial robot 10 of the type and class 
known as Model 363, manufactured by Cincinnati Milacron Inc., the assignee 
of the present invention. The robot 10 has a stationary base 11, 
supporting a platform 12 which is bi-directionally rotatable through 
approximately 300.degree. of rotary motion, around a vertical axis on the 
base 11 in response to a base drive (not shown). The robot platform 12, in 
turn, supports the coordinately movable assembly 13 used for maneuvering a 
work gripping device (not shown) which may be located on the end effector 
14. 
FIG. 2 illustrates the stationary base 11 of the robot 10 with the front 
cover plate 15 (FIG. 1) removed for clarity. The base 11 has a compartment 
16 formed by integral walls (FIG. 5). The compartment 16 supports a bottom 
plate 17, and a pair of vertical rectangular striker plates 18,19 are 
supported along their bottom edges 20,21 on the bottom plate 17. A 
rectangular elastomeric block 22 is snuggly fitted between the striker 
plates 18,19 to maintain plate separation. 
The rotatable platform 12 carries a rigid cylindrical pin, or stop lug 23, 
which has a head 24 affixed to the top side 25 of the platform 12. The 
stop lug 23 depends from the bottom 26 of the platform 12 and travels 
through a rotary lug path 27 defined in the robot base 11, which is 
obstruction-free until one or the other of the striker plates 18,19 is 
encountered. In the embodiment shown, the lug path 27 comprises a cast 
annular channel in the base 11, the lug 23 intercepts the striker plate 18 
for a short length below the top edge 28 of the plate 18. The lug 23 may 
be re-positioned in a variety of other pin-receiving sockets 29 to govern 
arcuate movement of the robot 10. Further, plural lugs 23 may also be used 
to define limits of arc-sector movement. 
Referring to FIG. 3, the striker plates 18,19 are seen to be loosely 
received between the back wall 30 of the base compartment 16 and the front 
cover plate 15. The plates 18,19 are backed up by left and right sidewalls 
31,32 in the compartment 16 so that they are only free to move toward one 
another, i.e. against the elastomeric block 22 (see FIG. 4). Relief cores 
33,34 are provided through the base compartment 16 to allow the plates 
18,19 to pivot smoothly. Thus, it can be seen that the rotary movement of 
the platform 12 along its horizontal plane will cause the lug 23 to 
contact the respective striker plate 18, and the plate 18 will tend to 
pivot about its bottom edge 20. The downward pivoting movement will 
compress the block 22, causing it to tend to bulge against the back wall 
30 and the cover plate 15, as shown by the phantom lines in FIG. 3. Thus 
controlled deceleration is achieved. The plate 18 is prevented from 
kicking back by the sidewall 32 of the compartment 16. In the event that 
the elastomeric block 22 is incapable of absorbing the stopping energy of 
the rotatable platform 12, or that the block 22 has deteriorated, the 
pivoting striker plate 18 will swing down to such position that the lug 23 
will no longer contact the top portion of the plate 18. The lug 23 will 
then pass over the elastomeric block 22 until it contacts the other plate 
19. The rigidly-supported backup striker plate 19 thus forms a positive 
stop for any overtravel movement. In the preferred embodiment, therefore, 
the plates 18,19 are spaced far enough to permit this overtravel. 
The controlled deceleration rate is predictable, depending principally on 
the characteristics of the elastomeric block 22, i.e. durometer rating, 
initial shape, etc. 
The exploded view of FIG. 5 illustrates the simplicity of construction, 
showing that the bottom plate 17, striker plates 18,19 and elastomeric 
block 22, are all merely inserted into the compartment 16, and are 
retained by the cover plate 15. A plurality of cap screws 35 fasten the 
cover plate 15 into position. 
It should be noted that while the elastomeric block 22 has been depicted as 
homogeneous, with a rectangular shape of constant cross-section, 
non-homogeneous or composite material having various shapes and 
cross-sections may be substituted to achieve desired deceleration 
characteristics. 
While the invention has been shown embodied in a robot having a rotary 
platform, it may be appreciated by those skilled in the art that the lug 
23; striker plates 18,19; and elastomeric block 22 components may be 
utilized for controlling linearly movable members as well, for example; 
gantry type robots having elevated rails and slide members. 
The invention may find use in other similarly-configured assemblies, such 
as machine tools and the like. It may also be appreciated that for 
unidirectional stopping, only one striker plate 18 is needed, and the 
elastomeric block 22 is then directly backed up by the compartment 
sidewall 31. 
Further, while the invention has been shown and described in connection 
with a preferred embodiment, it is not intended that the invention be so 
limited, but rather the invention extends to all such designs and 
modifications as come within the scope of the appended claims.