General purpose orthogonal axes manipulator system

A gantry type orthogonal axes manipulator system including a rack and pinion mechanical drive for the X and Y axis assemblies and a ball screw mechanical drive for the Z axis assembly employs closed loop DC servo electrical drives controlled by the conventional numerical control techniques. A rotary index feature permits horizontal rotation of the Y axis assembly, which supports the Z axis assembly, at the end of travel of the X axis assembly to service work zones on either side of the X axis assembly.

BACKGROUND OF THE INVENTION 
The general acceptance of industry automation as an essential requirement 
for improving productivity has increased the acceptance of the robot, or 
manipulator apparatus, as a mechanism for achieving automated industrial 
applications. 
Numerous robot configurations have been designed to meet specific 
industrial needs, i.e., cutting, welding, assembly, etc. The designs of 
many of the commercially available robots are unique to a particular 
application and employ complex mechanical design features and 
sophisticated software and control functions dedicated to the specific 
industrial application. 
The acceptance of robots as a useful industrial "tool" has resulted in a 
market demand for a robot system exhibiting the simplified design 
considerations of a machine tool suitable for control by conventional 
computer numerical control, direct numerical control and off-line 
programming with language such as Automatic Programmed Tool (APT). 
SUMMARY OF THE INVENTION 
The gantry design of the orthogonal axes manipulator system described 
herein with reference to the accompanying drawings reduces the complexity 
associated with conventional "shoulder/elbow/wrist" robot arms and permits 
programming in Cartesian coordinates as contrasted with the more 
complicated polar coordinates. The disclosed design provides a rigid 
manipulator that supports machine tool-type interpolation moves, high 
accuracy and repeatability while permitting robotic type velocity and 
dexterity. 
The gantry type design provides for an overhead X axis assembly supported 
by vertical structural members. The Y axis assembly extends as an arm from 
the X axis assembly and further supports a vertical Z axis assembly. In 
addition to the orthogonal X, Y and Z axes assemblies, a mounting surface 
on the Z axis assembly is designed to accommodate a multiple axes rotary 
wrist to which an appropriate end effector, i.e., gripper, welding torch, 
etc., can be attached. 
The open structure design of the gantry type robot system permits 
integration of positioners, conveyors, and other auxiliary units in either 
perpendicular or parallel orientation to the manipulator system to 
accommodate a work area of a production floor layout. The open design also 
provides easy access to the wrist, end effectors and working envelope of 
the manipulator system for ease of tool changes and maintenance. 
The mechanical drives associated with the X and Y axes assemblies are rack 
and pinion mechanisms which are driven by a DC drive motor-tachometer 
package that is direct-coupled through a 5:1 gearbox equipped with an 
anti-backlash resolver. The Z axis assembly utilizes a ball-screw 
mechanism with a fixed nut. The ball screw is anti-backlash direct coupled 
to a DC drive motor-tachometer package and is equipped with a power off 
brake. Way systems, or dual rail guide systems, employed in each 
orthogonal axis assembly consists of case-hardened rails. Each axis 
assembly includes a movable carriage coupled to the dual rail guide system 
by linear bearings. A control console responds to speed feedback 
information from the tachometers and position feedback information from 
the resolvers of each axis assembly to control the movement of the 
respective carriages in a closed loop arrangement. The direct coupling of 
the DC motor to the mechanical drive provides accurate, positive control 
of the movement of the carriage. 
The disclosed manipulator system may be programmed from a numerical control 
console, a teach pendant, or an off-line computer. To program the system 
with the teach pendant, command is obtained by selecting the teach pendant 
function on the control console, placing the system in the teach mode, and 
selecting a program number. This procedure transfers control of the linear 
motion of the X, Y and Z axes assemblies and the rotary motion of multiple 
axis rotary wrist to the pendant. The operator then manually runs the 
manipulator system through a complete cycle, programming each point, 
selecting fast or slow teach speeds or incremental jogs, to identify the 
process points, i.e. welding, assembly, etc. After completing the point 
programming with the pendant, the operator identifies operating functions 
such as subroutine calls, dwells, and running speed at the control 
console. The program is then recorded in memory. To run a program the 
operator simply selects a program at the console, puts the system in 
"auto-mode" and presses "cycle start". 
The machine tool design features of the manipulator system which enable it 
to be programmed for control by numerical control techniques provide 
operational capabilities that make it ideal for automated operation. These 
features include simultaneous control of all linear and rotary axis 
motion, circular and linear contouring, and the use of software limit 
switches. The disclosed manipulator system can be directly integrated with 
a direct numerical control system and has a capacity to interface with 
various peripherals and auxiliary equipment such as parts positioners, 
inspection equipment, conveyors, automatic fixturing, sensory feedback 
systems and other subordinate equipment and systems. 
The unique combination of sophisticated robot design with proven numerical 
control techniques bridges the gap between robot and machine tool 
technology.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 there is pictorially illustrated a manipulator system 
10 comprising three orthogonal axes assemblies consisting of the X axis 
assembly 20, Y axis assembly 40, and Z axis assembly 60. An optional 
multiple axis rotary wrist mechanism 80 is mechanically secured to the Z 
axis assembly 60 to accommodate an end effector T, which may typically be 
a gripper, a welding torch, etc. For the purposes of discussion it will be 
assumed that the wrist mechanism 80 is a commercially available two-axis 
rotary wrist. 
The operative combination of the X, Y and Z axis assemblies is supported in 
a gantry type configuration by the vertical support members SM which are 
secured to the floor F of the work facility. Machine tool type control of 
the operation of the manipulator system 10 is implemented by a 
conventional numerical control console CS, such as the PRODUCER.TM. CNC 
System which is available from the Westinghouse Electric Corporation. The 
orthogonal axis machine tool type configuration of the X, Y and Z axis 
assemblies elevated in the gantry configuration of FIG. 10 results in an 
optimized working envelope corresponding to the rectangular volume work 
zone Z. This gantry configuration of an orthogonal axis manipulator system 
significantly reduces the number of wrist articulations required to 
implement the desired work process, and further reduces requirements for 
auxiliary devices such as rotary tables. Pulse width modulated drive for 
the closed loop DC servo motor arrangements of each axis assembly is 
provided through the use of conventional drive circuitry located in the 
drive cabinet DS. The direct coupled DC servo motor arrangements include a 
motor-tachometer package and a resolver. The tachometer provides speed 
feedback information to the control console CS while the resolver supplies 
the control console CS with position feedback information directly from 
the drive motor. This provides a highly stable servo response. 
The application versatility of the orthogonal axis manipulator system 10 is 
typically illustrated in FIGS. 2, 3 and 4. In the embodiment of FIG. 2 the 
application of the system 10 for material handling and heavy parts 
assembly is illustrated. 
Sophisticated controls, precision operation and large working envelope 
provides the ability to trim, buff, drill and perform automated testing 
and inspection of large complex contours as illustrated in FIG. 3. 
Precise mechanical articulations permit application in welding and burning 
operations, as illustrated in FIG. 4. The open structure design of the 
manipulator system 10 tends to facilitate servicing of several production 
conveyors. 
The X axis assembly 20, as shown in FIGS. 1, 5A and 5B, consists of a 
closed cell type of construction which minimizes the torsional deflection 
of the X axis carriage 22 as it travels along the X axis guidance system, 
thereby providing desired system accuracy and repeatability. The X axis 
guidance system, or way system, includes 2, 3-inch diameter ground guide 
rails 23 and 25 which provide maximum rigidity and stiffness for the 
torsional-type bending modes. The dual rail way system, which is supported 
by the members SM, further assures a smooth, low friction travel of the X 
axis carriage 22 in response to the closed loop DC servo control. 
The X axis carriage 22 is coupled to the guide rails 23 and 25 by the 
linear bearings 24 which are preloaded and sealed in the housings 27 to 
protect the bearings from dirt. The bearings and rails are available from 
Thomson Industries. The guide rails 23 and 25 are protected from dirt and 
damage by bellows-type covers 29. 
The mechanical drive for the X axis assembly 20 is a rack and pinion 
mechanism consisting of rack 30 and pinion shaft 31 which is direct 
coupled to the DC motortachometer package 26 through a 5:1 gearbox 32 
equipped with an anti-backlash resolver 33. The gearbox 32 is designed 
such that the pinion shaft 31 is machined into the output shaft of the 
gearbox 32, thus preventing parts from coming loose or changing position. 
The direct coupling of the drive motors of the axis assemblies through low 
backlash drive elements minimizes lost motion. 
The rack and pinion mechanical drive has been selected for the X and Y axis 
assemblies to accommodate easy extension of the X and Y travel distances 
by adding additional sections of rack and extending the length of the 
guide rails. 
Several types of limit switches are associated with the X axis assembly 20 
including software limit switches which are stored in the memory of the 
control console CS, and hardware limit switches. The hardware limit switch 
package LS1 is provided for sensing end of travel of the X axis carriage 
22, and the home location of the X axis carriage 22. The hardware limit 
switches provide a back-up to the software limit switches and function to 
prevent "hard-stops" of the moving carriage 22 in the event the software 
limit switches are inoperative. 
A safety limit switch is further provided in the limit switch package LS1 
to subdivide the work zone Z of the system 10 into two discrete working 
sectors. If the system is not programmed to enter a given sector, any 
unpredictable attempts by the X axis carriage 22 to move into that sector 
will result in activation of the safety limit switch which in turn 
initiates a system emergency stop. The limit switch packages described 
herein are commercially available from the Micron Instrument Corporation. 
Electrical control and drive excitation for the system 10 from cabinets CS 
and DS is provided by cabling entering the junction box 36. 
The cabling for the manipulator system 10 as shown in FIGS. 1, 5A and 6A, 
extends from the junction box 36 at the end of the X axis structure 20 and 
continues through the flexible cable carrier 37 to a junction box 39 on 
the movable X axis carriage 22. 
The Y axis assembly 40, as shown in FIGS. 5A and 6A, functions as an arm 
extending perpendicularly from the X axis assembly 20. It includes a Y 
axis support member 41 and a double rail way arrangement comprising guide 
rails 42 and 44 to minimize the stresses and rotational deflections during 
the Y axis travel of the Y axis carriage 46 as well as during the 
positioning of the Z axis assembly 60 within the work zone Z. The guide 
rails 42 and 44 are protected by bellows covers 43. 
Of particular concern are the stresses concentrated at the point of 
attachment of the Y axis support member 41 with the X axis assembly 20 and 
the structural deflections which are transmitted to the wrist mechanism 
80. The Y axis support member 41 is uniquely designed, as illustrated in 
FIG. 6B, with a double taper T1 and T2 that effectively concentrates the 
mass of the support member 41 where the bending moment is highest, namely, 
at the interface with the X axis assembly 20, and reduces the mass at the 
end where the bending consideration is less. This design provides the 
advantage of reducing the moving mass of the Y axis assembly 40 thereby 
improving the overall accuracy of the manipulator system 10. The 
mechanical drive for the Y axis assembly 40 consists of a rack and pinion 
mechanism 45 similar to that described above with respect to the X axis 
assembly 20. 
The DC servo drive for the Y axis assembly 40, which is similar to that for 
the X axis assembly 20, includes a drive motor-tachometer package 51, 
gearboxresolver package 52 and a hardware limit switch package LS2 which 
provides end of travel and home location limits as backup to the stored 
software limit switches. 
The hardware limit switch packages LS1 and LS2 employed in the X and Y axes 
assemblies 20 and 40 mount on the back of the respective DC servo drive 
motors 26 and 51 to count the number of turns of the motor before 
actuating the limit switch either to an open or closed position to signal 
the control console CS that the respective assembly carriage has arrived 
at home location or has reached the end of travel limit. This limit switch 
package contrasts with the traditional toggle-type limit switches which 
are typically located at the end of the axis travel structures. The 
hardware limit switch packages associated with the motors reduce 
significantly the wiring complexity typically associated with the 
conventional toggle-type limit switch. 
The cabling associated with the Y axis assembly 40, as well as that 
servicing the Z axis assembly 60 and the wrist mechanism 80, is positioned 
in the cable carrier 48 which extends from the junction box 39 of the X 
axis carriage 22 to the junction box 49 of the Y axis carriage 46. The 
cable carrier 50, which is connected between the junction box 49 and the Z 
axis assembly junction box 57, services the Z axis assembly 60 and the 
wrist mechanism 80. 
The vertical Z axis assembly 60, as shown in FIGS. 5A, 7A and 7B, employs a 
ball-screw mechanical mechanism consisting of a ball screw 61 and a fixed 
nut 62 in combination with a way mechanism consisting of guide rails 64 
and 66 to transport the Z axis carriage 65 in response to the drive 
motor-tachometer package motor 63. The dual rail way mechanism functions 
similarly to that described above with respect to the X and Y axis 
assemblies 20 and 40. 
The mounting of the ball-screw mechanism is accomplished through the use of 
duplex bearings 67 and 68 at either end to provide the necessary stiffness 
to accommodate high RPM drive of the ball screw 61 by the drive 
motor-tachometer package 63. The drive motor-tachometer package 63 is 
connected to the ball screw 61 by an antibacklash coupler 69 which 
compensates for misalignment. 
As a result of the unique design of the Z axis assembly 60 there is no 
requirement for a counterbalance to compensate for the weight of the Z 
axis structure 60 and the ultimate payload which is manipulated by the end 
effector T affixed to the wrist mechanism 80. The drive motor-tachometer 
package 63 maintains the position of the Z axis assembly 60 during power 
on conditions. However, in a power off condition it is possible for the 
weight of the Z axis assembly 60 to back drive the ball-screw mechanism. 
Therefore a power off-brake on arrangement 70, which is commercially 
available from Electroid Inc., has been provided to prevent back driving 
of the Z axis assembly 60 during the power off conditon. 
The vertical Z axis assembly 60 has been designed such that the way system 
consisting of the dual guide rails 64 and 66, and the ball-screw mechanism 
are located on the centerline of the Z axis assembly 60 such that the 
vertical loads supported by the ball-screw mechanism act through the 
centerline of the assembly 60. 
The vertical Z axis assembly 60 is also equipped with a bellows-type cover 
72 to protect the ball-screw mechanism and the dual guide rails 64 and 66 
of the way system. The cable servicing the wrist mechanism 80 extends from 
the junction box 57 through the bellows cover 72. 
While the wrist mechanism 80 has been illustrated as being secured to the Z 
axis assembly 60, in those applications where the rotary motion 
capabilities of the wrist mechanism 80 are not required, the wrist 
mechanism 80 can be removed and the appropriate end effector T attached 
directly to the mounting surface 74 of the Z axis assembly 60. A hardware 
limit switch package LS3, similar to those described above, is mounted on 
the drive motortachometer package 63 and provides travel limit and home 
location information for the Z axis carriage 65. The commercially 
available limit switch package LS3 includes the resolver for the Z axis 
assembly. 
A rotary index unit 90, as illustrated in FIGS. 8A and 8B, increases the 
working envelope of the manipulator system 10. The unit 90 is located at 
the interface of the X axis carriage 22 and the Y axis assembly 40 to 
enable the Y axis assembly to be horizontally rotated 180.degree. at the 
end of travel of the X axis carriage 22 such that the return travel of the 
X axis carriage 22 permits servicing of a second rectangular volume work 
zone Z' on the opposite side of the X axis assembly 20 as shown in FIG. 1. 
A large preloaded bearing 91 is secured to the X axis carriage 22 by bolts 
92 and to the Y axis assembly 40 by bolts 93. A spline assembly 94, which 
is secured to the X axis carriage 22 by bolt 95, accepts the spline end of 
a drive shaft 96. The horizontal rotation of the Y axis assembly 40 is 
effected by a drive system consisting of a drive motor-tachometer package 
97 which is direct coupled to the drive shaft 96 via an anti backlash 
coupler 98 and a gear reduction unit 99. At the 0.degree. and 180.degree. 
motion end points, corresponding to the locations where the Y axis 
assembly 40 is perpendicular to the X axis assembly 20, a mechanical 
fastening arrangement 100 illustrated in FIG. 8B locks the Y axis assembly 
40 in position. 
Flat surfaces 102 and 104 are machined into the collar 106 of the Y axis 
assembly 40 at the 0.degree. and 180.degree. rotation points. Mechanical 
adapters 108 and 110, each including a wedge receptacle 112, are secured 
to the surfaces 102 and 104 respectively. When the Y axis assembly 40 is 
aligned with either the 0.degree. or 180.degree. rotation point, as 
indicated by a limit switch of the limit switch package LS4, the drive 
motor-tachometer package 97 is de-energized and a solenoid activated 
plunger device 120 is energized causing a wedge shaped plunger element 122 
to be inserted into the receptacle 112. This action locks the Y axis 
assembly in position relative to the X axis assembly 20. The wedge shape 
of the plunger element 122 compensates for any slight misalignment between 
the receptacle 112 and the wedge element 122. 
In the event an intermediate position is desired, such as 90.degree., to 
enable the manipulator system 10 to interface with a work station at the 
end of the X axis assembly 20, a mechanical adapter 130 can be secured to 
a flat surface 132 machined into the surface of the collar 106 at the 
90.degree. rotation point. 
A limit switch contained in the device 120 indicates whether or not the 
plunger element 122 is engaging the collar 106. The rotary index function 
effected by the DC servo motor 97 and the solenoid activated plunger 
device 120 is controlled by the control console CS in response to limit 
switch conditions of packages LS1 and LS4 and the limit switch of the 
device 120. A resolver may be coupled to the electric drive of the rotary 
index unit 90 to replace the function of the limit switches and provide 
servo control of the rotary index function. 
Inasmuch as the design of the manipulator system 10 is such that 
conventional machine tool programming and control techniques can be 
employed, the implementation of the control function associated with the 
system 10 may take one of several forms. The available programming 
techniques include the conventional teach by lead-through technique 
whereby the teach pendant 100 of FIG. 1 is provided and the system 10 is 
jogged through a series of point positions, with each point being recorded 
in the memory of the control console CS. A second type of programming 
instruction provides manual data input whereby an operator, using the 
keyboard K of the control console CS, can enter a program and have it 
stored in memory. 
Off-line programming is available through the use of post processor 
software to generate the necessary machine coding for use by the control 
console CS. A typical post processor software language is APT. 
A cathode ray tube display D provides the operator with information 
pertaining to the operation of the manipulator system 10. A commercially 
available system, such as the Westinghouse system described above, enables 
the operator to display the position of the end effector T, as well as 
access programs which have been placed in storage, modify programs and 
write new programs. Data entry via cassette and paper tape reader is also 
available. 
A basic servo block diagram schematic illustration of the control of the 
manipulator system 10 is illustrated in FIG. 9. The closed-loop servo 
configuration of each axis assembly, including the linear motion axes X, Y 
and Z and the rotary motion axis of the wrist mechanism 80 is funtionally 
depicted in FIG. 9. The control console CS includes a carriage position 
comparator 150 which compares a carriage command signal to an actual 
carriage position signal from the resolver 152 of the axis assembly 154 
and transmits a resultant carriage position signal through the amplifier 
156 to a carriage speed comparator 158. The speed comparator 158 compares 
the position signal to a velocity feedback signal from a tachometer 160 
coupled to the DC drive motor 162 which drives the carriage of the axis 
assembly 154 in response to a pulse width modulated drive 164. 
The carriage speed signal developed by the speed comparator 158 is supplied 
through an amplifier 166 to control the operation of the pulse width 
modulated drive 164 of the drive cabinet DS.