4. Software

The following sub-sections provide instructions for the installation of the Force Copilot software package. This allows you to get data from a force torque sensor.

• Section 4.1 and subsections refers to the control and programming for Universal Robots.
• Section 4.2 and subsections detail the installation of an open source development package, which can be adapted according to the users' needs. It currently functions with Windows and Linux.
• Section 4.3 links to ROS.
• Section 4.4 explains the Demo Software
• Section 4.5 will detail the use of serial communication in generic applications

4.1. Control with Universal Robots

Force Copilot contains many features to program and control the robot’s arm using a sensor’s force and torque readings. The package provides:

• ActiveDrive toolbar;
• Path recording node;
• Zero FT Sensor node
• Insertion node
• Find Surface node
• Force Control node
• Force Event node
• Collision Detection node
• Multipoint Path node
• Driver package.

4.1.1. ActiveDrive Toolbar

The ActiveDrive Toolbar is automatically installed with the Force Copilot software Package. It enhances the guiding mode on Universal Robots by allowing the robot to be hand guided smoothly and easily towards a waypoint. The ActiveDrive feature is a great way to assist the Path recording described in the Path Recording section, by hand guiding the robot while recording a path.

The robot speed set with the Speed slider will affect the speed at which the robot moves in the ActiveDrive mode. Verify and adjust the speed slider to the desired speed. It has to be greater than 50%.

4.1.1.1. Overview

Toolbar collapsed

Tap the ActiveDrive button to expand the toolbar.

Toolbar expanded

(Tap the mode selector to expand.)

ActiveDrive modes expanded

4.1.1.2. Features

4.1.1.3. Error Messages Overview

The ActiveDrive Toolbar will be automatically collapsed and be grayed whenever one of the following situations occurs. In such cases, by tapping the ActiveDrive button, the following messages will appear:

• Message:

  

• Solution:
  • Starting ActiveDrive while an excessive force is applied to the tool:
    • Determine if an external force is applied to the end-effector. If it is the case, tap OK and move the robot away from the obstacle (with Free Drive or Move tab), or remove any external forces and start ActiveDrive again.
    • If no external forces are applied, tap Zero Sensor.
• Message:

  

• Solution:

  • Force Torque Sensor is detected: Check the Force Torque Sensor’s connection. Make sure the USB adapter and all the wires are connected. Also, verify the Sensor’s LED status (refer to the Status LED section).

• Message:

  

• Solution:

  • The robot is not initialized: Tap OK and go to PolyScope’s home page. Tap Setup Robot and go to Initialize Robot to start the robot.

• Message:

  

• Solution:
  • A program is already running: The ActiveDrive Toolbar cannot be used while a program is running. Stop the program to enable the ActiveDrive feature.
• Message:

  

• Solution:
  • The speed setting of the robot is lower than 50%: The robot’s speed setting should be greater than 50%. Modify the speed setting in the robot program using the slider.

    

• Message:

  

• Solution:

  • If the Freedrive button is pressed: The ActiveDrive mode cannot be used when the Free Drive mode is ON. Make sure you are not pressing on the teach pendant’s Teach button when trying to use the ActiveDrive toolbar.

4.1.2. Using the force and torque values

Force Torque Sensor functions are made available in the Universal Robots functions drop-down menu.

• The rq_zero_sensor() function can be called at any point in a robot program to zero the force and torque values of the Force Torque Sensor.
• The get_sensor_Fx(), get_sensor_Fy(), get_sensor_Fz(), get_sensor_Mx(), get_sensor_My(), get_sensor_Mz() functions allow the user to assign the sensor values to any variable.
• The get_applied_tcp_force(<index>) function returns the current wrench (force and torque vector) value currently applied at the tool center point (TCP).
• The get_applied_base_force(<index>) function returns the current wrench (force and torque vector) value applied at the robot arm base.
• The express_force_in_frame(<T_from_to>,<wrench_from>) function is used to convert the wrench (force and torque vector) reading in a given reference frame into another (end-effector to robot base, and vice-versa, for example).
  • T_from_to = relative pose of the reference frame into which the wrench reading is converted
  • wrench_from = wrench to transform in pose or list format (Fx, Fy, Fz, Mx, My, Mz)

Fig. 4.1: Example of two reference frames for the express_force_in_frame(<T_from_to>,<wrench_from>) function

After the calibration has been completed, go to the FT 300 Dashboard to monitor the force and torque values in real time.

Prior to using the FT Sensor's data in the framework of a robot program, it is recommended to zero the sensor using the Zero sensor button.

Fig. 4.2: Force Copilot Dashboard with force and torque values displayed in real time.

4.1.3. Path Recording

The Force Copilot software package adds a Path feature in PolyScope which can be used to record paths directly by moving the robot. The ActiveDrive Toolbar is a great tool to use while recording a path, as it is an easy way to hand guide the robot’s end-effector. Path recording can be used for specific processes requiring complex paths (polishing, gluing, etc.) or more generally for any useful case that would require programming a high number of waypoints. The Path node offers options to modify the recorded path to change its speed and play the path backwards or relative to a variable start position.

How to add and record a path

4.1.3.1. Overview

4.1.3.2. Features*

* When an icon is greyed, it means it is unavailable.

If you tap the record button when a path is already recorded in a node, a warning pop-up will ask if you want to overwrite the path (tap OK) or keep the previously recorded path (tap Cancel).

4.1.4. Insertion nodes

The Force Copilot software Package includes Insertion nodes, which can be used to perform spiral, rotational and linear movements to insert objects in holes or bores, or to make contact with a surface. It is an essential integration resource for streamlining robot programs in the framework of precise assembly applications.

When the task is performed by a human operator, the operator's fingers provide valuable feedback through the sense of touch, thus allowing the human to detect any resistance when trying to insert a pin in a hole, for instance. To a certain extent, Force Copilot gives that kind of sensitivity to the end effector.

How to add an Insertion node

• From the PolyScope home page, tap Program Robot
• Create or load a robot program
• Go to the Structure tab and tap the URCaps submenu
• Select Insertion
• Tap the Insertion node in the robot program to edit it

4.1.4.1. Child nodes

1. Spiral button to insert a Spiral child node
2. Rotational button to insert a Rotational child node
3. Linear button to insert a Linear child node

Features (Spiral)

The Spiral child node is packaged with an On error condition line to be populated with a program instruction when/if the error condition occurs. The potential sequence after the Spiral instruction is followed by a program halt, by default.

1. Teach position button (Destination): Tapping this button saves the object's destination as a waypoint in the robot program
2. Reference frame dropdown menu (Direction): Menu used to select the frame according to which the tool will move in space
3. Axis dropdown menu (Direction): Menu used to select the direction in which the tool will go to reach the destination
4. Advanced parameters box: Box that expands the advanced parameters menu when ticked
5. Speed parameter: Textbox for the user to enter a speed value
6. Force initiating spiral move parameter: Textbox for the user to enter a force threshold value that triggers the spiral move, after the part/tool has established contact with the mating part/surface
7. Force initiating insertion parameter: Textbox for the user to enter a force drop value indicating that the part/tool has found the path of least resistance, prior to completing the insertion process
8. Radius increment per turn parameter: Textbox for the user to enter the distance between each spiral turn on the spiral radius
9. Enable peck mode box: Box that enables the retraction of the tool between points of contact
10. Maximum radius (Error condition): Textbox for the user to enter the maximum radius of the spiral, considering that no path of least resistance has been found

Default values and units of measurement

Features (Rotational)

1. Teach position button (Destination): Tapping this button saves the object's destination as a waypoint in the robot program
2. Reference frame dropdown menu (Direction): Menu used to select the frame according to which the tool will move in space
3. Axis dropdown menu (Direction): Menu used to select the direction in which the tool will go to reach the destination
4. Advanced parameters box: Box that expands the advanced parameters menu when ticked
5. Linear speed parameter: Textbox for the user to enter a speed value for the approach motion towards the destination
6. Force initiating rotation parameter: Textbox for the user to enter a force threshold value that triggers the rotation move, after the part/tool has established contact with the mating part/surface
7. Rotation speed parameter: Textbox for the user to enter a speed value for the rotational (indexing) motion
8. Maximum torque parameter: Textbox for the user to enter a torque threshold value used to prevent potential collision with objects during the rotational motion
9. Enable peck mode box: Box that enables the retraction of the tool between points of contact
10. Maximum rotation angle (Error condition): Textbox for the user to enter the maximum angle of the rotation motion, considering that no path of least resistance has been found

Default values and units of measurement

Features (Linear)

1. Reference frame dropdown menu (Direction): Menu used to select the frame according to which the tool will move in space
2. Axis dropdown menu (Direction): Menu used to select the direction in which the tool will go to reach the destination
3. Advanced parameters box: Box that expands the advanced parameters menu when ticked
4. Speed parameter: Textbox for the user to enter a speed value for the approach motion towards the destination
5. Force threshold parameter: Textbox for the user to enter a force threshold value that completes the linear motion
6. Maximum travel distance (Error condition): Textbox for the user to enter the maximum distance value which, upon being reached, means the force threshold has never been reached in the linear motion

4.1.5. Find Surface node

The Force Copilot software package includes the Find Surface node, which is a great tool for machine tending and various other applications that require repeated accurate positioning of objects.

The default parameters of the function allow for a versatile demo or a quick test of the features while the advanced parameters make it a more customizable asset.

How to add a Find Surface node

• From the PolyScope home page, tap Program Robot
• Create or load a robot program
• Go to the Structure tab and tap the URCaps submenu
• Select the Find Surface node
• Tap the Find Surface node in the robot program to edit it

1. Direction relative to the tool dropdown menu: Menu used to select the direction of the linear motion, relative to the tool
2. Zero Sensor Before Execution box: Box that inserts a Zero FT Sensor command right before the Find Surface instructions
3. Advanced parameters box: Box that expands the advanced parameters menu when ticked
4. Motion speed parameter: Textbox for the user to enter a speed value for the approach motion towards the destination
5. Maximum distance traveled (Stop condition): Textbox for the user to enter the maximum distance value which, upon being reached, means the force threshold has never been reached in the linear motion
6. Insert instruction textbox: Checkbox that inserts the corresponding stop condition in the robot program when ticked; its main function is to facilitate the programming and improve the user experience
7. Force threshold (Stop condition): Textbox for the user to enter a force threshold value that completes the linear motion
8. Insert instruction textbox: Checkbox that inserts the corresponding stop condition in the robot program when ticked; its main function is to facilitate the programming and improve the user experience

Fig. 4.3: Find Surface node with stop condition(s)

4.1.6. Using the Force Torque Sensor's Data in Force Nodes

In order to use the FT Sensor's data in Force control mode for all Force nodes, go to the Configuration tab and check the corresponding box. This will feed the Sensor's force values to the UR Force mode as an alternative to UR's embedded force feedback.

4.1.7. Force Control Node

4.1.7.1. Overview

The Robotiq Force Control node is used to apply force and torque values along and around axes.

How to add a Force Control node

• From the PolyScope home page, tap Program Robot
• Create or load a robot program
• Go to the Structure tab and tap the URCaps submenu
• Select the Force Control node
• Tap the Force Control node in the robot program to edit it

The Force Control node is primarily meant to be used with a Robotiq Path node.

With the various user-defined settings available, operators can use a force torque sensor to apply force/torque and thus follow irregular shapes and/or surfaces for applications such as polishing, deburring, finishing, dispensing, etc.

4.1.7.2. Features

Reference frame

The user can select a reference frame from a dropdown menu, as shown below.

The Tool reference frame uses the X, Y and Z axes of the end-effector to apply force and torque values in the appropriate direction.

On the other hand, the Base reference frame takes into consideration the X, Y and Z axes of the robot arm base.

Fig. 4.4: Force Control node with Reference Feature dropdown highlighted.

Parameters

1. Enable control: each checkbox corresponds to the enablement of force feeding along an axis (upper three options) or torque feeding around an axis (lower three options)
2. Force/Torque: depending on which options were checked at step 1, the corresponding textboxes here should be filled with the desired force/torque values
   1. Force values applied are in newtons (N) – the range allowed goes from -150 to +150 N
   2. Torque values applied are in newton-metre (Nm) – the range allowed goes from -50 to +50 N.

3. Stiffness: the stiffness settings act directly on the Sensor's directional compliance depending on the orientation of the end-effector and the axes selected at step 1.
   1. A stiffness value closer to 0% will provide greater compliance along/around the corresponding axis
   2. A stiffness value of 100% offers no compliance along/around the corresponding axis

4. Deviation range: the deviation range limits the flexibility allowed along/around the corresponding axis.
   1. The deviation range along the X, Y and Z axes is measured in millimeters (mm) – the negative range allowed goes from -1000 mm to 0 mm while the positive range allowed goes from 0 mm to 1000 mm.
   2. The deviation range around the X, Y and Z axes is mesured in degrees (°) – the negative range allowed goes from
      -179° to 0° while the positive range allowed goes from 0° to 179°.

Fig. 4.5: Deviation range - On the left, no deviation range has been entered. On the right, a deviation range of at least 15 degrees has been entered around the corresponding axis.

5. Enable adaptive stiffness: this checkbox greys out the stiffness values in the boxes at step 3 since the Force Control calculates the rigidity of the surface/object with which the end-effector comes in contact. Thus, constant force/torque values are applied to surfaces with variable rigidity (e.g.: long, bent, bending or folded sheets or parts).
   
   When entering into contact with a surface for the first time, the end-effector will pull back for it has reached the force/torque value entered at steps 2a and/or 2b. It will then go back to the surface and apply the same force/torque values while pulling back less and less over time.

Fig. 4.6: End-effector experiencing adaptive stiffness upon repeated contact with a surface

Test

The Test button applies the user-defined settings of the Force Control node to the sensor, therefore moving along/around the corresponding axes, if the control had been enabled for the latter, regardless of other instructions entered before or after the Force Control node in the program tree.

4.1.8. Force Event

The Force Copilot software package includes Force Event, which can be used to perform a click detection or to wait for a specific force or torque.

How to add a Force Event function

• From the PolyScope home page, tap Program Robot
• Create or load a robot program
• Go to the Structure tab and tap the URCaps submenu
• Select Force Event
• Tap the Force Event node in the robot program to edit it
• Select an operation to add to the Force Event sequence

1. Wait for Force function
2. Click detection function

4.1.8.1. Features (Click Detection)

The Click Detection feature monitors forces and torques throughout the nodes placed within it. This feature senses if a drop in the force or torque is then followed by a sudden rise, thus making a "click". If a click is detected within the Click detection node, the program then skips the remaining instruction lines that are included in the Click detection node. The program automatically goes to the following instruction.

Indeed, a program instruction can be added if no click is detected.

4.1.8.2. Features (Wait for Force)

The Wait for Force feature is used to detect a specific force or torque inside a Force Control node. The program waits until the force or torque is reached prior to the program continuation. The values are defined by the Force Control's force and torque parameters. To be sure the program is not incessantly running, a Timeout option is available.

4.1.9. Collision Detection

The Collision Detection feature is used to stop a program when the forces and the torques, monitored by the FT Sensor , exceed the defined limits. By default, the program does not monitor forces and torques.

How to add a Collision Detection

• From the PolyScope home page, tap Program Robot
• Create or load a robot program

• From the Installation tab:
  • Go to the Installation tab and tap the URCaps submenu
  • Select Force Copilot
  • Tap the Configuration tab to edit it

  

• From the Program tab:
  • Go to the Program tab and tap the URCaps submenu
  • Select Collision Detection
  • Tap the Collision Detection node to edit it

   

  You can either choose to halt (stop) or suspend (pause) the program when a collision is detected. The forces and torques monitored in the collision detection node are the ones measured by the FT 300 sensor. Thus, any forces or torques applied to the robot arm will not be detected. Only those applied to the end-of-arm tooling are monitored.

  

.

The Collision Detection feature in the installation tab can be configured to start the monitoring upon every robot program start. On the other hand, the Collision Detection node in the Program tab starts a thread that runs in parallel with the rest of the robot program. If the Stop monitoring option is selected in the Collision Detection node, the thread stops and the program continues without monitoring the force or the torque.

4.1.10. Multipoint Path Node

The Multipoint Path node is an advanced version of the Path node, combining complex trajectory recording and point-to-point teaching, with the option to define each segment as a straight line or as a curve.

How to add a Multipoint Path node

• From the PolyScope home page, tap Program Robot
• Create or load a robot program
• Go to the Structure tab and tap the URCaps submenu
• Select the Multipoint Path node
• Tap the Force Control node in the robot program to edit it

Fig. 4.7: Multipoint Path node (empty)

4.1.10.1. How to set up a Multipoint Path

Step 1

• Select the MoveJ To waypoint child node in the program tree.
• A menu will display in the Command tab.
• Using the Freedrive mode or the UR Move menu, move the robot arm to the position you want to be the starting point of your Multipoint Path.

• Tap the Set waypoint button. The UR waypoint interface will pop up and ask you to define the waypoint.
• Adjust the position if needed, then press OK.

At this point, the interface will look like this:

1. Tap the Edit button to open the UR waypoint interface and adjust the position of the robot arm (this works for every waypoint of the Multipoint Path)
2. Tap the Delete button to cancel the waypoint (deleting the starting waypoint will turn it to unassigned)
3. Tap and hold the Move here button to make the robot arm travel to the corresponding waypoint
4. Tap the Add line button to let the system know that a straight line will be linking the current waypoint and the next waypoint
5. Tap the Add curve button to let the system know that a curve will be linking the current waypoint and the next waypoint

Step 2

• Using the Freedrive mode or the UR Move menu, move the robot arm to the next desired position.
• Add another waypoint in the program tree by tapping the Add line or Add curve button.

Fig. 4.8: Multipoint Path interface with Line/Curve options.

Repeat step 2 until you complete your Multipoint Path.

Fig. 4.9: Representation of a six-waypoint Multipoint Path with both curves and straight lines.

4.2. Development Package

The Robotiq Force Torque Sensor development package can be downloaded at support.robotiq.com.

4.2.1. Distribution License

The development package is distributed under the New BSD license, which is a permissive free software license. In short, the provided code can be used in any project without any restriction regarding its use (commercial or not). If it is included in a software, this software does not need to be open-source. However, the code is provided "as is" without any liability from Robotiq and some restrictions apply regarding the distribution of the code and the use of the Robotiq name.

The terms of the license (included in each source file) are described here:

Software License Agreement (BSD License)

Copyright (c) 2014, Robotiq, Inc. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
disclaimer in the documentation and/or other materials provided
with the distribution.

- Neither the name of Robotiq, Inc. nor the names of its
contributors may be used to endorse or promote products derived
from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

4.2.2. Linux

4.2.2.1. Package Files – Description

The development package is structured with the following files and directories architecture (non-Linux files and directories are ignored in this section):

• src: contains the source files common to all platforms
• obj: used during compilation for the object files related to the common sources
• Linux: contains Linux specific files
  • bin: contains the binary files
  • src: contains the source files common to all platforms
    • main.c : application source file which can be modified by the user
  • obj: contains all the object files after they are compiled
• Makefile: file containing the rules to compile the sensor driver using Make

4.2.2.2. Procedure to Compile and Test the Provided Source Code

This procedure explains how to compile the source code and verify that the sensor data is properly read.

1. Unzip the package in the home folder, for example in the folder ~/driver/
2. Open a terminal and enter the package directory using the following command:

   rd@debian:~/$ cd driver

3. Use Make to compile the application:

   rd@debian:~/$ make linux

4. In order to have access to the virtual serial COM port, add the used username to the group dialout:

   rd@debian:~/$ sudo usermod -a -G dialout username

5. It is required to log out (or reboot) the session in order for the group change to become effective.
6. Make sure that the sensor is properly powered and that the data signals are connected to the development PC using the provided RS485 to USB converter. A new device named ttyUSBx should be present in /dev, which can be verified with the following command:

   rd@debian:~/$ ls -l /dev | grep ttyUSB

7. In a terminal, go to the ~/driver/Linux/bin folder and execute the demo application using the following command:

   rd@debian:~/driver/Linux/bin/$ ./driverSensor

8. After 1-2 seconds, the sensor data should start showing up in the terminal as a vector of 6 floats with data in the (Fx, Fy, Fz, Mx, My, Mz) format.

Fig. 4.10: Sensor Data Acquisition.

4.2.2.3. Adapt to a User Application

In practice, the provided source code will be adapted to either: be incorporated with a custom application or to communicate with one. At this point, the main.c file should be adapted according to the guideline comments inserted in the code.

4.2.3. Windows

4.2.3.1. Package Files – Description

The development package is structured with the following files and directories architecture (non-Windows files and directories are ignored in this section):

• src: contains the source files common to all platforms
• obj: used during compilation for the object files related to the common sources
• Windows: contains Windows specific files
  • bin: contains the binary files
  • src: contains the source files common to all platforms
    • main.c : application source file which can be modified by the user
  • obj: contains all object files after they are compiled
  • Data_logger: contains an application (and its source code) to log data from the sensor
  • compiler.bat: script which automates the settings for the environment variables and the compilation of the example application
• Makefile: file containing the rules to compile the sensor driver using Make

4.2.3.2. Procedure to Compile and Test the Provided Source Code

This procedure explains how to install MinGW, compile the provided source code and verify that the sensor data is properly read.

1. Unzip the package in the desired directory.
2. If it is not already installed, download MinGW at http://www.mingw.org/. Download the installer "mingw-get-setup.exe".
3. Install MinGW by running "mingw-get-setup.exe" and save the default installation path.
4. Open "MinGW installation manager".
5. Select "mingw-developer-toolkit" in the "Basic setup" tab and click "Mark for Installation".
6. Select "mingw32-binutils" in the "All packages" tab and click "Mark for Installation".
7. In the menu "Installation", click "Apply changes". This will install the required packages to compose the software using Make.
8. In the Windows directory, run the compiler.bat file. This will build your application.
9. Run the application "driverSensor" located in the "Windows/bin/" folder.
10. After 1-2 seconds, the sensor data should start showing up in the command window as a vector of 6 floats with data in the (Fx, Fy, Fz, Mx, My, Mz) format.

Fig. 4.11: Sensor Data Acquisition Under Windows.

4.2.3.3. Adapt to a User Application

In practice, the provided source code will be adapted to either: be incorporated with a custom application or to communicate with one. At this point, the main.c file should be adapted according to the suggested comments inserted in the code.

4.3. Visual Demo Software

The Visual Demo Software is used to demonstrate the ability of the FT Sensor to read force and moment. It is not intended to be used for programming or to save or use data. It can also be used to calibrate the Sensor. Please refer to the Calibration Procedure for the Visual Demo Software (PC) section for the calibration procedure.

4.3.1. Software Package Installation

1. Make sure that you have the latest version of the Visual Demo Software, which can be found at support.robotiq.com.

   

2. Copy all the files of this folder onto a PC.
3. Connect the USB connector to the converter attached to the PC. Important : The Sensor must NOT be powered at this time.
4. Wait while the driver(s) install. After all the drivers have been installed.
5. Plug the Sensor cable into the Sensor.
6. Connect the Sensor cable to the power supply.
7. Launch the demo application.

   

8. You should see a COM port in green with a serial number, showing the Sensor connected to the PC. Click on it.

   

By going into the Sensor Data tab, you can now see in real time the force and moment applied on the FT Sensor.

4.4. Serial Communication

The FT Sensor uses two communication modes, Modbus RTU and data stream. The Modbus RTU communication mode is used to obtain information on the Sensor, like its firmware version. The data stream mode is used to obtain data from the Sensor.

4.4.1. Modbus RTU

The FT Sensor can be controlled over USB using an ACC-ADT-USB-RS485 signal converter. This section is intended to provide guidelines for setting up a Modbus scanner that will adequately communicate with the Sensor.

For a general introduction to Modbus RTU and for details regarding the CRC algorithm, the reader is invited to read the Modbus over serial line specification and implementation guide available at: : http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf.

For debugging purposes, the reader is also invited to download one of many free Modbus scanners such as the CAS Modbus Scanner from Chipkin Automation Systems available at: http://www.store.chipkin.com/products/tools/cas-modbus-scanner.

4.4.1.1. Connection Setup

The following table describes the connection requirements for controlling the Sensor using the Modbus RTU protocol:

In Modbus RTU you can obtain the following information:

4.4.1.2. Read Holding Register (FC03)

Function code 03 (FC03) is used to read the status of the Sensor (robot input). Examples of such data is the display of the current force and torque values.

Example of FC03 Read Function:

To get Fx, you need to read (03) the register 180 (00B4) in device ID 9 (09).

Request is: 09 03 00 B4 00 01 C5 64

Hex format: 0x09 0x03 0x00 0xB4 0x00 0x01 0xC5 0x64

To get all 6 force/torque values at once, you need to read (03) six registers (0006), starting with register 180 (00B4) in device ID 9 (09).

Request is: 09 03 00 B4 00 06 04 A6

Hex format: 0x09 0x03 0x00 0xB4 0x00 0x06 0x84 0xA6

4.4.2. Data Stream

Data stream mode is the recommended method of obtaining data from the Sensor. Once initiated, the Sensor will stream force and moment data continuously until communication is interrupted by the user.

For a setup over Universal Robots, Data stream will be accessible on TCP port 63351 of your machine.

To stop the data stream, communication must be interrupted by sending a series of 0xff characters to the Sensor. Sending for about 0.5s (50 times) will ensure that the Sensor stops the stream.

When the stream is started, 16 bytes messages are sent by the sensor at 100Hz using this format:

<0x20><0x4e><LSB_data1><MSB_data1> ... <LSB_data6><MSB_data6><LSB_crc><MSB_crc>

With dataX being a 16-bits signed integer defined as:

The CRC is computed using a standard 16-bits modbus CRC (see http://www.ccontrolsys.com/w/How_to_Compute_the_Modbus_RTU_Message_CRC).

4.4.2.1. Preset Multiple Registers (FC16)

Function code 16 (FC16) is used to activate functionalities of the Gripper (robot output). A common example is the initialization of data streaming.

Example of setting multiple registers (FC16):

To initialize the data stream, 0x0200 must be written with the function 16 (0x10) in register 410 (019A).

Request is: 09 10 01 9A 00 01 02 02 00 CD CA

Hex format: 0x09 0x10 0x01 0x9A 0x00 0x01 0x02 0x02 0x00 0xCD 0xCA