5- or 6-Axis Gantry Robot Device Module
The standard gantry robot module is designed to control a five or six degree-of- freedom gantry robot which consists of three mutually perpendicular linear joints and a two or three degree-of-freedom revolute wrist. The enhanced gantry robot module has the added capabilities of the split-axis option and backlash and linear compensation.
Module Specifications
Minimum V+ compatibility: 10.2, 10.4
for 6 axis configuration -10.2 (10.4 recommended)
for 5 axis configuration -10.4V+ License Requirements:
for standard - “Kinematics License”
for enhanced - “Enhanced Kinematics License”If you install a module for which you do not have a license, an “*Option not installed*” message will be displayed when you restart your system.
Device module name: GNT, EGN
for standard - GNT
for enhanced - EGNDevice Module Identification Number: 3, 19
for standard - 3
for enhanced - 19This number is displayed along with the robot serial and model number after the system boots up and whenever the ID monitor command is issued. (Note: In V+ 10.2 to 10.5, the enhanced module has ID# 3.)
Default Startup Message:
for standard - “5/6-Axis Gantry Robot”
for enhanced - “Enhanced 5/6-Axis Gantry Robot ”The startup message is displayed just after the system boots up.
Default Joint Configuration (for V+ 11.0 and higher):
Joint
Axis
Board/Channel
1
1 (X)
1/1
2
2 (Y)
1/2
3
3 (Z)
1/3
4
4 (roll)
1/4
5
5 (pitch)
2/1
6
6 (roll wrist)
2/2
Robot Option Word
The default value of the robot option word is zero (0), i.e. all bits off. See the AdeptMotion VME Developer’s Guide or the SmartMotion Developer's Guide for details on setting the robot option word.
Bit 1: Split X-axis option
Turning on bit 1 (the least significant bit) of the robot option word enables the split X-axis option. Two motors are used to move the X-axis, the first and last motors. See the document Split-Axis Device Module Feature for more information on this feature.
Bit 2: Backlash and linear compensation option
Turning on bit 2 (counting from 1; mask value 2) of the robot option word enables the backlash and linear compensation option. Backlash compensation is enabled on all axes. In V+ 10.5 and higher, linear compensation is enabled on all axes of this module. (In V+ 10.2 to 10.4, linear compensation may only be applied to the X, Y, and Z axes.) See the document Backlash and Linear Compensation for more information on configuring backlash and linear compensation.
Bit 4: Wrist linearity compensation applied in motor space
If bit 4 (counting from 1; mask value 8) is off (default), the wrist linearity compensation will be applied in joint space and is interpreted as a joint-value correction in degrees or mm. If this bit is set, wrist linearity compensation will be applied in motor space and is interpreted as encoder values in raw encoder counts. (Linearity compensation of the X, Y, and Z axes is always in joint space, regardless of the setting of this bit . This bit has no effect if compensation is not enabled. This bit also has no effect on backlash compensation.)
Warning
Note that the encoder scaling factor is usually many hundred or thousand encoder counts per degree: it is therefore essential that if you change the wrist compensation mode bit that you also change the corresponding values in the linear correction table.Bit 9: Motor software limits
The robot option word also determines whether software limits on motor motion (in addition to the standard limits on joint motion) are to be used. If bit 9 (counting from 1; mask value 256) is set, then software limits on motor motion are used. Motor motion limits are in units of encoder counts and can be set from the "Motor Motion Parameters" menu in SPEC.
Axis Configuration
The axes of the motion are defined in the list that follows, also see Figure 1.
Joint 1 is a linear axis that moves in the world X direction. A positive displacement of the joint moves the robot in the positive world X direction.
Joint 2 is a linear axis that moves in the world Y direction. A positive displacement of the joint moves the robot in the positive world Y direction.
Joint 3 is a linear axis that moves in the world Z direction. A positive displacement of the joint moves the robot in the negative world Z direction.
Joint 4 is a revolute (roll) joint whose axis of rotation is parallel to the world Z-axis. A positive rotation of the joint turns the robot's end effector in a direction opposite to positive rotation around the world Z-axis.
Note
The direction of positive rotation about the world X, Y, and Z axes is defined by the right-hand rule (with thumb of right hand pointing in direction of axis, fingers curl in direction of positive rotation about the axis).
Joint 5 is a revolute (pitch) joint whose axis of rotation intersects the axis of rotation of joint 4. In most instances, the axis of rotation of joint 5 is designed to be perpendicular to the axis of joint 4. In this configuration, the skew angle between joints 4 and 5 is defined to be –90 degrees and the joint 5 axis of rotation is horizontal. For any skew angle, when joint 4 is positioned at zero degrees, the joint 5 axis of rotation will lie in a world Y-Z plane. When joint 4 is positioned at zero degrees and the skew angle is –90 degrees, the joint 5 axis of rotation will be parallel with the world Y-axis and a positive rotation of joint 5 will rotate the robot's end effector in a direction opposite to positive rotation around the world Y-axis.
Joint 6 is a revolute (roll) axis whose axis of rotation defines the nominal Z-axis of the robot's tool frame of reference. That is, if a NULL tool is defined, the Z-axis of the tool frame will be collinear with the axis of rotation of joint 6. The gantry robot module requires that joints 4, 5, and 6 be designed such that the axis of rotation of all three joints intersect at a single point. In addition, the skew angle between joints 5 and 6 must be equal to the negative of the skew angle between joints 4 and 5. That is, when joint 5 is positioned at zero degrees, the axis of rotation of joint 6 must be collinear with the axis of joint 4. When joint 5 is zero, a positive rotation of joint 6 turns the robot's end effector in a direction opposite to positive rotation around the world Z-axis.
The origin of the world X/Y/Z system can be arbitrarily selected to be any point with respect to the frame of the gantry.
As with all robot modules, the standard V+ BASE and TOOL transformations can be used in combination with the geometric model to specify and compute the end point of the robot relative to the world coordinate frame.
Maximum operating range of rotational joints
These modules have three rotary joints. Their maximum operating range is as follows.
Joints 4, 5: –179.9° to +179.9°
Joint 6: –359.9° to +359.9°Warning
Be sure to set the software joint limits properly before attempting to move the robot in a V+ program. It is especially important for revolute axes to have correct software limits set before attempting any motion instruction. If the limits are improperly set, a revolute axis can rotate unexpectedly in order to stay in range.Variations in Axis Configuration
These modules can be configured as either a 5- or 6-axis gantry robot. In the five-axis configuration, the final roll axis (joint 6) is excluded. In addition, the skew angle between joints 4 and 5 can be configured. Normally, joint 5 is oriented perpendicular to joint 4 and the skew angle is –90 degrees. However, any skew angle between 0 and –180 degrees is permitted.
See the document Split-Axis Device Module Feature for information on configuring a split X-axis.
Geometric Dimensional Constants
Tool Z-offset – this is the distance from the intersection of axes 4 and 5 to the center of the tool mounting flange (see Figure 1).
Link dimensions – there are 7 dimensional constants that must be defined to specify the geometric conversions performed by this module. All 7 numbers are functions of the skew angle between joints 4 and 5 (see Figure 1). In the table below, "a" is the value of the skew angle.
Link Dimension Parameters for Gantry Robot
Parameter
Units
Value
LA
Tool Z-offset distance
mm
LB
Link dimension value #1
degrees
a
LC
Link dimension value #2
–
sin (a)
LD
Link dimension value #3
–
cos (a)
LE
Link dimension value #4
–
sin2 (a)
LF
Link dimension value #5
–
cos2 (a)
LG
Link dimension value #6
–
sin (a) cos (a)
LH
Link dimension value #7
–
cos (a) / sin (a)
Figure 1. Link Definitions and Dimensions for the Gantry Robot
Interpretation of Cartesian Rotations
During program generated straight line motions, the Cartesian rotation interpolation algorithms emulates the rotations of the three wrist joints. Therefore, the three maximum Cartesian rotational speeds and acceleration times should be set equal to the maximum joint speeds for the three wrist joints.
Coupling Between Robot Joints and Motors
These modules require that each of the first three motors only affect the motion of a single linear axes. Therefore, three scale factors define the positional relationships between the first three motors and the X/Y/Z linear axes of the robot.
However, since most "roll", "pitch", "roll" wrists are implemented with some degree of coupling between motor rotations and wrist joint movements, a full 3-by-3 coupling matrix is used to describe an arbitrary coupling scheme between the motions of the last three motors and the three wrist joints.
See the document Split-Axis Device Module Feature for information on the split-axis option, which allows two motors to couple into the motion of joint 1 (the X-axis).
Robot Configuration Control Program Instructions
The following robot configuration control program instructions are utilized by a 6-axis gantry robot to specify the range of motion for joint 5:
FLIP, NOFLIP
If the wrist is in the NOFLIP'ed pose, when the position of joint 5 is computed from a transformation value, joint 5 is restricted to an angular range of 0 to +max range. If the wrist is FLIP'ed, joint 5 is restricted to the negative angular range (-0.00...1 to -max range). For robots with only 5 joints, the sign of the joint-5 angle is uniquely derived from the transformation value so FLIP/NOFLIP is ignored.
In addition, the following configuration program instructions affect the range of motion for joints 4 and 6:
SINGLE, MULTIPLE
If SINGLE is in effect, when a transformation is converted to joint angles, values for the angular position of joints 4 and 6 are restricted to the range –180 to +180 degrees. When MULTIPLE is in effect, the full range of motion for joints 4 and 6 will be utilized.
See the V+ Language Reference Guide for more information on these instructions.
The following robot configuration control program instructions do not have any effect upon the operation of mechanisms controlled by this module:
RIGHTY, LEFTY, ABOVE, BELOW
Additional Restrictions
None.
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Last modified on:
11/28/2007
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