Programmable breakaway clutch system with collapsible failure mode

A breakaway clutch for robot end-of-arm tooling includes a housing and movable member constrained within the housing for movement along a central axis. A tool connecting member is linked to the movable member by way of a capsule-shaped link. The tool connecting member is located such that a movable member is in the normal position and the tool connecting member is movable in all directions except in the direction of a front housing wall. The movable member is biased toward the normal position, with the biasing being adjustable to vary the bias and thereby vary the sensitivity of the clutch to forces applied to the movable member by way of the tool connecting member. Movement of the movable member away from the normal position is sensed to send an alarm signal to the robot controller.

TECHNICAL FIELD 
This invention relates to robotic tooling, and more particularly to an 
overload sensitive clutch for connecting a tool to the end of a robot arm. 
BACKGROUND OF THE INVENTION 
A problem in the use of robots in tooling operations is the problem of 
overload on the robot arm. This may occur if the robot arm or tool 
collides with something or if the tool gets stuck in the workpiece. 
Several devices have been proposed and are in use that detect stresses and 
overloads on the robot arm and immediately shut down the robot when 
overload is detected in order to avoid damage to the robot or to the 
workpiece. These devices include expandable breakaway joints and 
connectors that break away when the robot arm experiences an overload. 
For example, the devices shown in our U.S. Pat. Nos. 4,717,003 and 
4,848,546 are expandable clutches useful in most robotic tooling 
situations. It has been found, however, that a collapsible clutch is 
preferable for use when the tool is an arc welding electrode, as 
collisions with the work piece are a more common occurrence. An expandable 
clutch as shown in our previous patents may not trip at a low enough 
threshold to protect the welding torch from damage if a collision puts the 
clutch into a compression failure mode. It has also been found that the 
ball and socket type of connection utilized in our expandable clutches is 
inappropriate for use in a collapsible clutch due to excessive friction 
between the parts, causing nonrepeatability. 
SUMMARY OF THE INVENTION 
The invention includes an adjustable clutch for use with robot end-of-arm 
tooling that provides a means for sensing movement of a tool attached to 
the clutch. The clutch includes a sealed piston movable member held within 
a chamber. The movable member is attached by a link to a tool connecting 
toggle. The piston is capable of lateral movement within the chamber, and 
the sensitivity of the breakaway clutch is adjusted by biasing the 
movement of the piston. In the preferred embodiment, the piston is biased 
using spring means and by introducing pressurized air into the piston 
chamber. A sensing device detects movement of the toggle relative to the 
clutch to shut down the robot when an overload is encountered. 
The present invention provides a breakaway clutch having a collapsible 
failure mode. The clutch is ideal for use with arc welding tooling. The 
clutch has a sensor capable of detecting movement of the tool in relation 
to the clutch and of tripping an emergency stop when the movement is 
beyond a predetermined range of movement allowed. The clutch restores 
itself to a normal position when the overload is relieved. 
According to one embodiment of the invention, the clutch includes a clutch 
housing that defines a piston cavity, a piston contained within the 
cavity, and a toggle that is attached to the piston through the housing by 
a link. The clutch includes biasing means to bias the piston in a 
direction toward the toggle. The toggle has locating means for positioning 
the piston in a normal operational position in relation to the housing and 
proximity sensing means for sensing deviations of the toggle from its 
normal position. In a preferred embodiment, the link is a capsule-shaped 
solid body engaged with frustroconical/spherical internal walls in the 
piston and toggle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention provides an "on the fly" adjustable clutch for use with robot 
end-of-arm tooling. The clutch is positioned between the robot arm and the 
tool and provides a means for sensing motion of the tool relative to the 
clutch that would indicate an overload on the system. The clutch is 
adjustable under program control so as to vary the load capacity and 
resistance of the clutch to handle various types and sizes of tools with 
varying sensitivity and is therefore ideal for use in interchangeable 
tooling systems. The clutch may be used in combination with a robot having 
an emergency stop, or other stop means, so that when an overload is sensed 
by the clutch it trips the emergency stop thereby preventing damage to the 
robot, the tool or to the workpiece. 
Referring initially to FIGS. 1 and 2, a clutch 10 according to the present 
invention attaches an arc welding torch 12 to end 14 of robot arm 16. 
Torch 12 is shown in position to weld workpiece 18. The exterior portions 
of clutch 10 include a housing 20, a toggle 22, electrical connector 24, 
and a compressed air line 26. Torch 12 is attached to toggle 22 by way of 
arm 28. It is important to sense forces and moments on torch 12 in the X, 
Y and Z directions, so that abnormal forces and moments may be utilized to 
shut down robot arm 16. Forces in the Z direction are sensed in order to 
enable a compression failure mode. 
Referring now to FIGS. 3A and 3B in addition to FIGS. 1 and 2, clutch 10 is 
attached to end 14 of the robot arm by way of bolts 100 extending through 
rear mounting plate 102 into an insulating robot adapter plate 104. Plate 
104 is attached to the robot arm by way of bolts 106. 
Housing body 108 is a generally tubular member having circular 
cross-sections about central axis 109. A rear housing wall 110 includes a 
rear cavity wall 111. Side housing wall 112 has an inner side cavity wall 
113. A front housing cover 114 provides a forward cavity wall 116. Front 
housing cover 114 has a centrally located opening defined by wall 118. 
Front housing cover 114 and housing body 108 are fixed to rear mounting 
plate 102 by way of bolts 120 and locating pins 122. 
A movable member includes piston 130 and O-ring 132 confined within the 
cavity formed by walls 111, 113 and 116. Wall 113 is cylindrical about 
central axis 109. Movable member 128 is capable of linear movement along 
central axis 109 from a normal position within the cavity shown in FIG. 3A 
wherein piston 130 is spaced apart from rear cavity wall 111. Movable 
member 128 is movable in the direction of rear cavity wall 111 to a 
position where piston 130 contacts wall 111, as shown in FIG. 3B. Movable 
member 128 includes an inwardly tapering frustroconical internal side wall 
134 joined to a semi-spherical internal end wall 136. Internal side and 
end walls 134 and 136 are coaxial with central axis 109 and open in the 
direction of front cavity wall 116. A tool connecting member 140 includes 
toggle 22 and arm 28. Tool connecting member 140 has an external end 142 
adapted for connecting clutch 10 to a tool. Tool connecting member 140 has 
an internal end 144 within the cavity, and internal end 144 has 
inwardly-tapering frustroconical internal first and second side walls 146 
and 148, respectively, joined to a semi-spherical internal end wall 149. 
Internal side and end walls 146, 148 and 149 are coaxial with central axis 
109, and open in the direction of the rear cavity wall 111. 
Link 150 spans between tool connecting member 140 and movable member 128. 
Link 150 is a capsule-shaped solid body having a cylindrical side wall 
151. Link 150 has semi-spherical external end walls 152 and 154 engaging 
with internal end walls 136 and 149, respectively, in the movable member 
and tool connecting member. Movable member 128 and tool connecting member 
140 are spaced apart by link 150, and forces upon tool connecting member 
140 are applied to movable member 128 by way of link 150. 
Tool connecting member 140 is located within the cavity by way of conical 
seats 160 and spherical pins 162. Preferably, five seats 160 and pins 162 
are provided in a asymmetrical pattern to provide a single return 
orientation for tool connecting member 140. Seats 160 are fixed in front 
housing cover 114. Tool connecting member 140, link 150 and movable member 
128 are dimensioned such that movable member 128 is in the normal position 
shown in FIG. 3A when tool connecting member 140 is located such that pins 
162 are seated in seats 160. Tool connecting member 140 is movable in all 
directions except in the direction of front cavity wall 116. 
A spring 170 biases movable member 128 towards the normal position 
established by the linkage to tool connecting member 140 and the locating 
pins and seats. Movable member 128 is also biased towards the normal 
position by way of variable air pressures applied through air line 26 to 
the cavity by way of passageway 172. Thus, the sensitivity of clutch 10 to 
forces and moments applied to the movable member 128 by way of the tool 
connecting member 140 is variable. 
Movement of the movable member 128 away from the normal position shown in 
FIG. 3A is sensed by way of a microswitch 180 fixed within electrical 
connector 24. Microswitch 180 is actuated by a bearing ball 182 
constrained for linear movement within a cylindrical wall 184 formed in 
housing body 108. 
Referring now to FIGS. 4 and 5, internal side wall 134 in piston 130 
preferably has a taper A of about 13.degree.. First internal side wall 146 
of toggle 22 preferably has a taper B of about 137.degree., and second 
internal side wall 148 preferably has a taper C of about 52.degree.. 
In operation, any compression force on tool connecting member 140 having a 
component in the Z direction or a moment having a component in the X or Y 
direction will apply force by way of link 150 to movable member 128. If 
the force and/or moments exceed a threshold predetermined by the bias on 
movable member 128 by way of spring 170 and air pressure in line 26, 
movable member 128 will shift away from the normal position shown in FIG. 
3A to a position exemplified by FIG. 3B. In FIG. 3B, movable member 128 
has moved in the direction of rear cavity wall 111 to an extent that 
bearing ball 184 has been allowed to move inwardly. In the normal 
position, bearing ball 184 is forced outwardly by piston 130, thereby 
causing microswitch 180 to indicate normal operation. When bearing ball 
184 shifts inwardly due to movement of movable member 128, microswitch 180 
sends an alarm signal to the robot controller. 
An important feature of the invention is the capsule-shaped link 150, which 
allows a virtually friction-free linkage between toggle 22 and piston 130. 
The spherical end walls of link 150 allow unlimited relative rotation 
between the two members, while compression forces are transmitted by the 
linkage. The linkage exerts a virtual perpendicular friction-free load 
between toggle 22 and piston 130. 
Having described only a single embodiment of the invention, it will be 
apparent to those skilled in the art that there may be many changes and 
modifications to this invention without departing from the spirit and 
scope of the invention.