Universal Robots CB3 Use and care manual

Kinematic Calibration Manual for CB3
Copyright c 2009–2020 by Universal Robots A/S
Version 3.13

Contents
1 Plate Calibration 1
2 Dual Robot Calibration 2
2.1 RequiredEquipment....................................................... 3
2.2 Mounting the Robots to the Calibration Horse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 AccessingtheFunctionality.................................................. 4
2.4 SafetySettingsoftheRobots ................................................. 5
2.5 Network Connection Between the Robots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5.1 Master/SlaveConnection.............................................. 7
2.5.2 Manualmode ...................................................... 7
2.6 Beforestarting ........................................................... 8
2.7 Mounting the UR Dual Robot Calibration Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.8 Measuring Positions and Calibration Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.9 ApplyingtheCalibration.................................................... 12
2.9.1 Validation ......................................................... 12
2.9.2 ResetCalibration .................................................... 14
3 Program Correction by Key-waypoints 15
3.1 Introduction............................................................. 15
3.2 AccessingtheFunctionality.................................................. 16
3.3 RedefineKey-waypoints .................................................... 17
3.3.1 CorrespondingToolPosition............................................ 18
3.3.2 WaypointsfromMultiplePrograms....................................... 19
3.4 HandlingKey-waypoints.................................................... 19
3.5 CorrectingaProgram ...................................................... 20
Appendices 23
A Dual Robot Tools 23
B Robot DH Parameter 24
B.1 UR3................................................................... 24
B.2 UR5................................................................... 24
B.3 UR10 .................................................................. 24
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1. Plate Calibration
1 Plate Calibration
NOTE:
Plate Calibration will not be available in versions of the Calibration Manual after and including
Version 3.10
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2. Dual Robot Calibration
2 Dual Robot Calibration
This manual is a step-by-step tutorial for integrators that describes how to perform Dual Robot Calibration of
the kinematics. The method can be used on Universal Robots—with Software version 3.0.16000 up to version
3.3 and later.
The method is patented pending under the patentCalibration and Programming of Robots, Søe-Knudsen,
Rune (inventor); Petersen, Henrik Gordon (inventor); Østergård, Esben Hallundbæk (inventor), IPC: B25J9/16,
Patent number: EP2012/068337, September 18, 2012. International Publication number WO 2013/045314 A1.
Figure 2.1: The Dual Robot Calibration method.
CAUTION:
Stay clear of the robot when using Dual Robot Calibration.
CAUTION:
Not all calibrations are good calibrations. Please pay attention to the generated statistics
before saving the result of the calibration. If a calibration is not performed with care, the
robot may become inaccurate.
The method requires a Dual Robot Calibration kit from Universal Robots (purchase number: 185500) and
one pair of UR3, UR5 or UR10 robots, respectively, with a CB3 control box. The robot bases are connected
with the Calibration Horse and the robot tools are connected by the Tool Connector, see Figure 2.1. This
creates a closed chain where the distance between the bases and the tools are fixed to known distances. When
the robots has been connected it can perform a number of measurements from coordinated movements to
different positions. This creates a set of data which creates a mathematical foundation for determining the
robot arm lengths and link rotations of the robots, i.e. the Denavit-Hartenberg parameters.
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2. Dual Robot Calibration
2.1 Required Equipment
The method requires a Dual Robot Calibration Kit from Universal Robots (purchase number: 185500) and
one pair of UR3, UR5 or UR10 robots with control box CB3. The robot bases are connected with a device
and the robot tools are connected by a device (Appendix A). This creates a closed chain where the distance
between the bases and the tools are fixed to known distances. In addition, the calibration horse, (Figure 2.2),
have holes with threads at the bottom for temponary and long term storage of screws.
Please note that the UR3, UR5 and UR10 are mounted differently on the Calibration Horse and that their
cables are pointing toward each other, as illustrated in Figure 2.2.
UR5
UR10
UR5
UR10
Cable
Cable
UR3
UR3
Figure 2.2: A sketch of the Dual Robot Calibration Horse and where the UR3, UR5 or UR10 robot can be
mounted
To complete the assembly, mount the two handles at each end of the Calibration Horse with two M8-
1.25x25, each. The handles and screws are included in the Dual Robot Calibration Kit.
Required equipment:
•A pair of UR3, UR5 or UR10 robots, respectively, to be calibrated
•A stand with a height of at least 0.5 m for the Calibration Horse
•Dual Robot Calibration Kit from Universal Robots with purchase number: 185500, including:
–The UR Dual Robot Calibration Horse with alignment pins (Figure A.1, Appendix A)
–The UR Dual Robot Calibration Tool Connector with alignment pins (Figure A.2, Appendix A)
– Four M8-1.25x70 to mount the Calibration Horse to the stand (may differ depending on the robot
stand)
–Eight M8-1.25x25 screws with washers to mount UR5 and UR10 robots to the Calibration Horse
– Eight M6-1.0x25 screws with washers to mount the robot tools to the Calibration Tool Connector
–Eight M6-1.0x25 screws to mount UR3 robots to the Calibration Horse
–One Go tool used in the validating procedure, (Figure A.3, Appendix A)
–One No Go tool used in the validating procedure (Figure A.4, Appendix A)
Exception:
• The alignment pin for the tool connector, should not be used when calibrating UR5s produced prior to
end of 2014. This is due to the calibration requiring an improved version of the tool flange in UR5.
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2. Dual Robot Calibration
2.2 Mounting the Robots to the Calibration Horse
(1) Mount the Calibration Horse to a stand of a height of at least 0.5 m and mount the robots to the
Calibration Horse, as in Figure 2.3.
(2) Mount two robots of the same type and version on the Calibration Horse, see Figure 2.3.
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2
Figure 2.3: Mount the robots on the Calibration Horse, connecting the robot bases
(3) From the Initialization screen set the robot mounting and angle (click the "Configure Mounting" button),
see Figure 2.4:
UR3:
(a) The Tilt is approximately 52,5◦±5◦and
(b) The Rotate Robot Base Mounting is 270◦.
UR5 and UR10:
(a) The Tilt is approximately 52,5◦±5◦and
(b) The Rotate Robot Base Mounting is 90◦.
(4) From the Initialization screen set the payload to 0 kg for both robot types, see Figure 2.5.
Figure 2.4: Mounting of the robot Figure 2.5: TCP settings
2.3 Accessing the Functionality
The starting point for the method is to enable Kinematics Calibration in Expert Mode.
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2. Dual Robot Calibration
Figure 2.6: Select Kinematics Calibration in Expert Mode.
This takes you to the Calibration screen. It also enables a new button called "Calibrate robot" on the
"Welcome screen", should you need to return to the Calibration screen at a later time. Clicking the "Kinematics
Calibration" button again removes the new button from the "Welcome" screen.
Select Dual Robot Calibration in the "Calibration" tab, see Figure 2.7.
Figure 2.7: Select Dual Robot Calibration to select the method.
2.4 Safety Settings of the Robots
(5) Go to the Installation tab and click on Safety. Unlock the Safety tab and in the General Limits select and
apply the Least restricted safety preset limits before performing the dual robot calibration (see Figure
2.8).
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2. Dual Robot Calibration
Figure 2.8: Safety settings
2.5 Network Connection Between the Robots
The Dual Robot Calibration screen appears as shown in Figure 2.9. There are a number of options to choose
from within connection types which are described below:
• Master - the robot acts as master of the calibration process. Make sure that the other robot is selected
as Slave and that the two robots are connected with a network cable or switch.
• Slave - the robot acts as a slave in the calibration process. Make sure that the other robot is selected as
Master and that the two robots are connected with a network cable or switch.
• Manual - the robot acts as a master, but the slave robot is selected by an user supplied IP-address (see
description below).
Figure 2.9: Network options in Dual Robot Calibration.
The different connection types Master/Slave or Manual are described below.
(6) Connect the robot controllers with a network cable or through a network switch.
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2. Dual Robot Calibration
(7) Use either the master/slave or manual connection method to establishment network connection
between the two robots controllers.
Note: Robot 1 is the master robot and Robot 2 is the slave.
2.5.1 Master/Slave Connection
A Master/Slave connection works by connecting two robots via a network cable or over a network switch. One
robot must be selected as master and the other as slave. Selecting one of these cases sets up the IP address
automatically.
CAUTION:
Notice that the IP-addresses 10.17.17.18 and 10.17.17.19 will be used for master/slave
connections. Connecting the robots to a local area network may interfere with other devices
having the same IP.
(8) When the slave (Robot 2) is ready and has entered the screen in Figure 2.10, press Connect network on
the master to establish the network connection, see Figure 2.11. The screens that follow are described
in Section 2.7.
Figure 2.10: Slave mode Figure 2.11: Master mode
NOTE:
Network communication between the Master robot and the Slave robot can break down,
causing the calibration screen to change as displayed in Figure 2.12.
Figure 2.12: Network Communication break during calibration
2.5.2 Manual mode
Selecting Manual leads to the screen in Figure 2.13.
(9) In Figure 2.13, Enter the IP number or host name of the Slave by clicking the text field with the text "IP
address or host name".
(10) Connect by press Connect network, see Figure 2.13.
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2. Dual Robot Calibration
Figure 2.13: Manual enter IP address
2.6 Before starting
The steps through the calibration are by default done automatically, unless it needs help from an operator.
This can be disabled by the Auto step checkbox, see Figure 2.14.
Figure 2.14: Calibration options
Furthermore, It is optional to save and correct the home position of each robot, which can be relevant if
only one of the robots need to be calibrated. However it is by default enabled.
Save calibration - means that the calculated kinematic calibration is applied and saved on the robot
Correct home position - means that it estimates and sets the home position using the calibration
(define new joint offset angles).
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2. Dual Robot Calibration
2.7 Mounting the UR Dual Robot Calibration Connector
The robots are now ready to be physically connected if the robots are in their home position, see Figure 2.15.
(11) Ensure that the robots are in the Home position.
(12) Continue the procedure by pressing Connect Robots, see 2.16. If the robots are not in home position, a
pop-up will ask to move the robot to home (see Figure 2.17), before trying again.
Afterwards the robots will move into position as shown in Figure 2.18, ready to be connected.
Figure 2.15: Robots moved to the home position Figure 2.16: Press Connect robots to begin connection
the robots together, physically
Figure 2.17: Message telling that step no.: 11 was not
performed. Press OK and move the robot to Home
Figure 2.18: Robots ready to be connected
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2. Dual Robot Calibration
(13) Attach the tool connector to the master robot (Robot 1) as in Figure 2.19.
(14) When the tool is mounted on the master robot (Robot 1), Press Proceed in the pop-up Figure 2.20.
(15) The slave robot (Robot 2) now enters free drive mode. Move the slave towards the connector and attach
the screws with washers. When done it looks like the fully connected robots shown in Figure 2.21.
(16) When the slave robot (Robot 2) is also mounted on the tool, Press Proceed in the pop-up Figure 2.22.
This step also starts the robot measuring each other by moving around.
Figure 2.19: Device connected to the master robot Figure 2.20: Proceed when the tool is mounted on
the master robot (Robot 1)
Figure 2.21: Robots fully connected Figure 2.22: Proceed when the robots are connected
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2. Dual Robot Calibration
2.8 Measuring Positions and Calibration Statistics
After step no.: 16, the robot will begin measure and identify the calibration. First a number of initial measure-
ments are collected. A preliminary calibration is calculated from those. Second, the final set of measurements
will be done and the final calibration will be calculated, see Figure 2.23 and 2.24.
Figure 2.23: Collecting measurements Figure 2.24: Calculating the calibration
Afterwards, a statistic is given that describes whether the found calibration is usable (shown in green, see
Figure 2.25) or problematic (shown with red, see Figure 2.26).
If the result was successful as expected and the Auto step box is checked, it will automatically continue to
step no: 17.
If the result was unsuccessful, the calibration procedure will not be able to continue. Calibration may fail
for various different reasons. Please use one or more of the troubleshooting hints listed below and start a new
calibration by going back to step 1:
•Check that security settings are set to least restricted (see step 5).
• Remote the tool connector and unmount the robots from the calibration horse. Clean all surfaces on
the robots, the calibration horse and the tool connector. Remount the robots while making sure that
nothing is stuck between the parts.
• If one or more joints have been replaced, then check that they are mounted correctly. For example,
check that the screw washers are on the correct side of the output flange.
•If one or more joints have been replaced, then adjust the joint’s zero position (see Service Manual).
Figure 2.25: Successful calibration Figure 2.26: Problematic calibration
The section Calibration Results contains the statistics for the accuracy of the found calibration. The
Control Results are statistics for a number of control measurements done throughout the calibration process
which only are used to validate the calibration.
The statistics are given in two units: millimeters (mm) and milliradians (mrad) which refers to the RMS
deviation in Cartesian space. The statistics contains the fields:
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2. Dual Robot Calibration
Mean deviation: The average deviation in millimeters and in milliradians between the positions mea-
sured by the first and second robot
Standard deviation: The standard deviation calculated on basis of the above
Max deviation: The maximal measured deviation
Expected results
The calibration is passed successfully if:
•Mean deviation will be less than 1 mm and 2 mrad
•Standard deviation is less than 0.5 mm and 1 mrad
•The different between the Calibration and Control results is not more than 50% different
2.9 Applying the Calibration
After step no: 16 the calibration is applied to the controller. The calibration is permanently saved after
succesful validation. Then the robots are ready to be disconnected.
(17) A pop-up appears as shown in Figure 2.27. Dismount the screws from the connector and press Proceed.
If the Auto step box is checked, the robots will continue with correcting the robots’ home position.
NOTE:
If you tap Proceed without removing all of the screws from the tool connector on the slave
robot, each robot can make a protective stop. To resolve the problem, verify all screws are
removed and clear the Protective Stop/s. Once this is done, press Proceed again.
Figure 2.27: Remove screws
CAUTION:
If either robot enters a Protective Stop while disconnecting, you must remove the Tool Con-
nector and jog the robots to separate them manually. Once the robots are separate and the
Protective Stop is cleared, the disconnection dialog box reappears on PolyScope and you can
retry the step.
2.9.1 Validation
Next follows a validation procedure. Here both robot tool flanges need to be completely free from e.g. screws
and alignment pins.
(18) Remove the Calibration Tool Connector and alignment pins etc. and Proceed with the validation, see
Figure 2.29. The robots TCP will now approach one another.
(19) Verify that the distance in-between the robot tools is within a distance of 2.5 mm ± 1 mm using the Go
and No Go tools, see Figure 2.30.
(a) Verify that the 1.5 mm Go tool can pass in-between the two robot’s tool flanges
(Figure A.3, Appendix A)
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2. Dual Robot Calibration
(b) Verify that the 3.5 mm No Go tool can not pass in-beween the two robot’s tool flanges
(Figure A.4, Appendix A)
(20) If the verification is successful in step no. 19, Proceed to the next validation step, see Figure 2.31.
Figure 2.28: Robots ready for the validation procee-
dure
Figure 2.29: Proceed to the Verification procedure
when the Calibration Tool Connector, screws, and
alignment pins are removed from the robots tool
flange
2.5mm +/- 1mm
Figure 2.30: Verification by alignment of tools Figure 2.31: Proceed if the verification in step no. 19
is successful
Secondly the robots will move to their new calibrated home position. Here it is important that the robots
are fully stretch out and that the tools are pointing in the right direction, like in Figure 2.32. After completion
of step no. 22 the Dual Robot Calibration procedure has been completed, see Figure 2.34
(21) Verify the robot home positions, see 2.32.
(22) If the verification is successful in step no. 21, Proceed to the next validation step, see Figure 2.33.
(23) Save the calibration
(24) Calibration done, press Exit, see Figure 2.34.
Figure 2.32: Verify the robots new home position Figure 2.33: Proceed if the verification in step no. 21
succeed
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2. Dual Robot Calibration
Figure 2.34: Kinematic Calibration is done
2.9.2 Reset Calibration
The calibration can manually be adjusted or reset by editing the /root/.urcontrol/calibration.conf file placed
together with the other configurations. To reset the calibration all decimal and hex numbers is reset to zero
like in Listing ?? in page ??.
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3. Program Correction by Key-waypoints
3 Program Correction by Key-waypoints
This tutorial describes how to perform an automatic program correction of key-waypoints, so that a program
can be moved from an uncalibrated robot to another and still work. The technique can also be used to make
programs work after e.g. replacements of joints in a robot.
Figure 3.1: Illustration of the correction
The functionality is available on Universal Robot controllers with software version 1.7, 1.8, 3.3 and onwards.
3.1 Introduction
NOTE:
Before starting with program correction, backup your original program e.g. by saving it under
a new name. Once a program has been corrected and subsequently saved again, it cannot be
corrected again.
With properly selected and redefined key-waypoints, it is possible to make a model which describes the
difference between the old and the new robot. After the model has been built, the programs are corrected
when loaded. The model can be extended/improved at any time by defining more key-waypoints. The model
is specific for each installation file on the robot.
The quality of the model is determined by the number of key-waypoints and the accuracy with which they
are defined. If further correction is desired, the model can be improved by adding more key-waypoints at a
later time.
The accuracy of a corrected waypoint correlates with the quality of the model, and the distance to the
nearest key-waypoint.
Note that currently the program correction functionality does not support the following:
•Other types of waypoints besides fixed waypoints
•Waypoints contained in the "BeforeStart" program node
•A "Move" node which has a selected feature for the motion (different from the "Base" feature)
•A "Move" node which sets a selected TCP for the motion.
The unsupported program nodes mentioned above might need to be corrected manually after the auto-
matic correction process has completed.
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3. Program Correction by Key-waypoints
3.2 Accessing the Functionality
The starting point for the tutorial steps is as follows:
(1) From Expert Mode on the controller screen enable calibration by toggling the "Kinematics Calibration"
button.
Figure 3.2: Select "Kinematics Calibration" in Expert Mode to enable the calibration functionality.
(2) This takes you to the Calibration screen. It also enables a new button called "Calibrate robot" on the
"Welcome screen", should you need to return to the Calibration screen at a later time. Clicking the
"Kinematics Calibration" button again removes the new button from the "Welcome" screen.
(3) The next screen contains a new tab called "Calibration". This tab offers three options. Choose "Program
correction - by key-waypoints".
Figure 3.3: Select "Program correction–by key-waypoints".
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3. Program Correction by Key-waypoints
3.3 Redefine Key-waypoints
The program used in this tutorial is a simple pick and place program with two key-waypoints, the waypoint
for the pick and place positions.
(4) The chosen program can now be loaded by pressing "Load Program":
Figure 3.4: Press "Load Program" to import a program.
(5) Select one of the decided key-waypoints in the program. In the program tree, waypoints that are not
reteached are displayed in italics and with the undefined waypoint icon. The waypoint called "pick" is
selected:
Figure 3.5: Select one of the key-waypoints. In this case waypoint named "pick"
(6) Press "Change this waypoint" to redefine the configuration for the selected waypoint:
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3. Program Correction by Key-waypoints
Figure 3.6: Press "Change this waypoint" to redefine the configuration for this waypoint.
(7) This leads to the "Move" tab. Move the robot to the new position and press "OK".
3.3.1 Corresponding Tool Position
To help the method, it is important to adjust the Corresponding Tool Position (CTP) which is the offset from
the endpoint of the robot with or without e.g. picked objects. Examples of typical CTP locations:
•The tool center point where the robot is going to pick an object.
•The end location of the object where the object is going to be placed.
This value is used in the process that redefines the waypoint. The CTP can be defined individually for
each key-waypoint which improves the accuracy of the correction. The selected Tool Center Point (TCP) from
the program installation is used as default.
(8) Specify the Corresponding Tool Position by pressing "Change CTP":
Figure 3.7: Press "Change CTP" and change the Corresponding Tool Position.
(9) Change the CTP coordinates and press OK:
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