Introduction

With RoboDK TwinTool calibration you can automatically calibrate the tool center point (TCP). Industrial robots are highly repeatable, but not accurate. Therefore, the accuracy of an industrial robot can be improved through robot and tool calibration. Without calibration, robot accuracy highly depends on the robot brand and model.

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RoboDK TwinTool can be used to calibrate and validate the tool center point (TCP). The TwinTool can accurately calibrate the TCP for tools with spherical or conical geometries.

1.Spherical tools➔The center of the tool is calibrated

2.Conical tools➔ The tip of the tool is calibrated

Requirements

You must install the RoboDK TwinTool App and have a compatible sensor to perform the automated tool calibration.

Make sure to have the following:

1.One or more robot arms.

2.A compatible dial indicator (also known as LVDT or linear gage).

3.RoboDK software must be installed and an appropriate license for automated robot calibration must be available.

4.You need compatible robot drivers for your robot controller.

5.Install the RoboDK TwinTool App:

a.Download the RoboDK TwinTool App (contact RoboDK for a download link)

b.Double click the file to install the app and open it in RoboDK.

c.Select Tools➔Apps and double click on TwinTool to see the TwinTool toolbar and menu.
If you are unable to see the TwinTool app you should close RoboDK and start RoboDK again with administrator privileges to properly install the app.

Note: RoboDK Apps require the App Loader plugin to be enabled. This plugin should automatically be loaded when double clicking the rdkp file. If it is not the case, you can load the App Loader plugin in Tools➔Load Plugin.

Important: The TwinTool App automatically downloads and installs dependencies, which requires an active Internet connection. However, it is possible to download these dependencies from another computer.

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Note: The TwinTool menu and toolbar may be displayed automatically. You can show or hide the TwinTool App (or other apps) by selecting Tools➔Apps List and double clicking the Enabled tag of the app.

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Linear gage sensor

RoboDK TwinTool supports multiple linear gage sensors, including Keyence, Mitutoyo, Sylvac and others. Some communication protocols include USB, Ehternet/IP and RS232. An approximated price for an industrial grade linear gage sensor is 1,500.00 Euros.

The linear gage sensor should have an accuracy of 0.005 mm or better and a travel of 10 mm or more. It is recommended to have a measurement frequency of 50 samples per second or more. This sensor is not provided or sold by RoboDK. We recommend contacting your local distributor to supply this sensor required to use RoboDK TwinTool.

The following list shows a sample order for a Keyence linear gage:

●Keyence GT2-P12 - Pencil type gage

●GT2-UB1 - USB connection unit

●OP-87716 - Cable extension

●OP-76875 - Suggested mounting bracket for the gage

●25 mm flat contact point with M2.5x0.25 thread needed (not provided by Keyence)

The following list shows a sample order for a Mitutoyo linear gage:

●Mitutoyo 542-191 - LG 100 gage

●Mitutoyo 542-081A - EJ Counter + AC

●Mitutoyo 21HZA149 - USB interface (RS232 also supported)

●25 mm flat contact point with M2.5x0.25 thread needed (not provided by Mitutoyo)

Calibration Setup

To calibrate the tool (TCP) using TwinTool you need to load the robot in RoboDK and make sure the sensor and the robot are connected. You can optionally model the cell by adding the 3D models of objects and tools. This will allow to automatically avoid collisions.

1.Load the robot:

a.Select File➔Open online library. The online library will show up in RoboDK.

b.Use the filters to find your robot.

c.Select Open to automatically load the robot in your RoboDK station.

d.Alternatively, download the robot file directly from the library (https://robodk.com/library) and open the file with RoboDK (the .robot file).

2.Connect the sensor:

a.Connect the sensor to your computer.

b.Select TwinTool➔ Measure.

c.Make sure the sensor is measuring and measurements are stable.

Note: If you are not able to connect to the sensor right away, you will be able to edit the connection settings and save them for later use during the next steps.

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Important: Make sure the setup is rigid enough for calibration by making sure that vibrations nearby don’t alter the measurements. For example, place the robot on the sensor and try creating small vibrations (such as walking near the area of the sensor). Measurement should remain stable within less than 0.005 mm of noise. If this is not the case, it is strongly recommended to enforce the support of the sensor and/or the robot base.

3.Connect the robot:

a.Select Connect➔Connect robot.

b.Enter the robot IP and port.

c.Select Connect.

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Note: Some robot controllers require following a specific setup or specific software options. More information in the robot drivers section.

4.Select Get Position from the robot connection panel. This step will update the position of the robot in RoboDK.

Customized setup

Important: It is recommended to model your cell load 3D models any objects that can cause collisions with the robot or the tool. If you have a tool that can cause collisions with the robot (or any other potential collisions) it is better to proceed with a customized setup as described in the next section.

You can optionally follow these steps to properly model the 3D environment of you cell.

1.Load the 3D model of your tool and create a tool in RoboDK. More information in the create tool section.

2.Load any 3D files to model the cell. You can load 3D STEP, IGES, STL files. More information in the getting started section.

Note: It is strongly recommended to properly model the cell to avoid collisions.

Tip: If you have a good estimate of the tool center point you can set it up in RoboDK and update the estimated tool to have a faster calibration procedure.

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Calibration Wizard

To start the calibration procedure, simply select TwinTool➔ TwinTool Wizard.

After launching the wizard, you will be guided through the Calibration, Validation, or Simulation setups. This includes setting up the connection to the sensor, ensuring a valid state of the robot and review of key parameters. Follow the steps on screen and refer to the tool tips if you need additional details.

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Important: It is recommended to run the calibration sequence in simulation mode at least once before calibrating on the connected robot.

Important: The simulated sequence may not match the real sequence used for calibration or validation. The robot path is adjusted automatically.

Tip: Save the Joint Target of the robot position on the sensor, using a different name that ‘Calib Target’. You can reuse it to quickly move the robot back into position.

Tip: Set the Estimated tool error to 5 mm or less if you already have a good TCP estimate. This will make the calibration procedure faster.

Tip: Change the joint range in Z and XY to change the range of motion for the robot.

Calibration Results

After the calibration sequence completes, you will be directed to the Analyze tab of the wizard. From there, you can visualize current and previous calibrations and validations, delete or re-apply calibrations, and more.

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By clicking the Calibration button, you will see a chart showing the calibration results. The tool center point (TCP) is calculated using the nominal robot kinematics.

Note: Select TwinTool➔

TwinTool Wizard to start the calibration sequence again with a different set of points (the sensor should not be moved).

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Tip: If you want to obtain the best accuracy results it is important to calibrate the tool with different robot configurations. For example, if you first run a calibration sequence with the robot in flip position (Joint 5 negative), you can teach a new target having a non-flip position (Joint 5 positive) and run the calibration sequence again.

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Validation

Once you have run the calibration sequence you can run some validation tests. These validation tests can be in the same location of the sensor or different locations.

Important: It is not possible to combine multiple calibration sequences done in different locations of the linear gage. You can calibrate the robot more than once in the same location and all data collected in the same location of the sensor will be used for calibration.

Validate the tool calibration

Select Validate from the Wizard. The calibration data will be used to calculate the TCP (excluding robot calibration). You will then be directed to the Analyze tab of the wizard. The calculated TCP will be displayed, and some statistics will provide estimated errors for the calculated TCP.

Select Validation to display a summary and some statistics about the results. These statistics correspond to the planar errors detected by the sensor.

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Tip: Taking more measurements for calibration can remarkably improve the calibration results. You can change the sensor target measurement (for example, use an 8 mm target after the default 4 mm target for a second calibration). You can also change the robot configuration to take measurements on the same point but with different joint angles (for example, using the flip and non-flip configurations).

Settings

This section describes additional settings and options that you can modify to better customize your calibrations and test the robot accuracy.

Calibration Settings

Select TwinTool➔Advanced Settings to open the complete list of advanced settings. Most of these settings are prompted and set through the Wizard.

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