The MiR Serial interface is a generic interface protocol suitable for interfacing, for example, PLCs to the MiR mobile robot platform. The interface offers possibilities of setting new positions, starting and stopping robot mission execution, and making 100 32 bit integer and 100 64 bit floating point registers available for the user to store process variables, mission parameters, and other data.

The registers can be used as a shared memory interface for data sharing between the mobile robot, the device connected through the serial port, and devices using the built-in REST interface. Through this device, the system can be programmed for example to wait for a certain register to be set before proceeding on a mission, which can be useful when waiting for a PLC controlled process to finish or a button to be pressed before continuing.

In addition to this, the interface offers the possibility of a limited interaction with the mission subsystem of the MiR robot by for example retrieving a list of available missions and queueing, starting, and aborting missions in the mission queue.

Things you'll need

Serial Interface works on all MiR robots as long as the robot has at least one free USB port.

To install and configure a USB to serial adapter to use with the MiR Serial Interface, you must have a compatible USB to serial adapter available.

Serial protocol

Specifications

The parameters of the Serial Interface are as listed in the table below. The values marked in bold are the default values. The parameters of the interface can be configured by editing a configuration file, see Installing a USB to serial adapter.

MiR robots support USB to RS232 converters based on the FTDI chipset. MiR recommends that you buy a FTDI-based USB to RS232 from http:/www.ftdichip.com/Products/Cables/USBRS232.htm.

Installing a USB to serial adapter

This section describes how to install and configure a USB to serial adapter to use with the MiR Serial Interface. For this, you must have a compatible USB to serial adapter available.

The USB to serial adapter can be installed in the top-mounted USB ports if the physical layout of the top module allows it, and if the port is not occupied by a top camera. If the top-mounted USB port is occupied, it is possible to use the USB port, going to the service port under the front corner.

To install a USB to serial adapter, follow the steps below:

Step 1: Sign in to the robot interface, and go to System > Settings > Serial Interface.

Step 2: Plug in the USB to serial adapter.

Step 3: Under External adapter serial number, select Detect .

Step 4: Check the command response in the dialog box. If the detectin was successful you will receive the message: "Serial adapter successfully setup".

Step 5: Modify all parameters to the desired values. Select Save changes when all changes have been completed.

Step 6: Unplug the USB to serial adapter, and insert it again to make the changes take effect.

Automatic activation of the Serial Interface node

When using the serial interface, the Serial Interface node is automatically activated. However, you can manually start and stop it under the Launch Menu, which is located under System > Processes.

Interface Protocol

Command set

There are two basic ways of interacting with the robot via the serial protocol: setting parameters by prefixing a command with !, or retrieving parameters by prefixing a command with ?.

All commands must be terminated by the carriage return character \r with the hexadecimal value of 0x0D. The response sent back will be terminated by a carriage return character \r as well.

Commands – special notes

Some commands and associated return values in the command set of the MiR Serial Interface deserve special attention. The commands are listed in this section for easy reference.

When handling dynamic strings on devices, such as PLCs, some of the replies utilize fixed positions for the return values to allow for the device to index directly to the values they require.

Please note that the commands are case sensitive, and the serial interface will therefore not accept lower-case letters as commands.

Set Register - !R

The syntax of the command is !R<n>#<value>\r, with !R being the Set Register command, <n> being the number of the register, for example 37, # being the value specification character, and <value> being the value, for example 82. In this case, the complete command would be !R37#82\r.

For registers 101-200, the syntax of the command is basically the same, but it allows floating point values. An example of such a command is !R101#3.1459\r for setting register 101 to the value of 3.1459.

Get Register - ?R

The syntax of the command is ?R<n>\r, with ?R being the Get Register command and <n> being the register to query for value. An example of such a command is ?R101\r to get the value in register 101.

The return string of the command is formatted as follows: OK: R%i#%i\r in the case of registers 1-100 and OK: R%i#%lf\r in the case of registers 101-200. The register number will be filled with leading zeroes, so that ?R7 returns OK: R007#1234\r. Another example of a reply from a floating-point register is OK: R101#3.1459\r, denoting a value of 3.1459 in register 101.

Get Current Position - ?P

By querying with the Get Current Position command, it is possible to get the position of the MiR robot in the internal coordinate system. The units of the coordinate system are in meters and the resolution of the positions given are in centimeters.

The origin of the coordinate system is the point where the mapping procedure started. This means that an X/Y position will not necessarily be at a corner of a map, but most likely somewhere inside it. Error: Reference source not found shows the axes of the coordinate system used in the MiR robot. The X coordinate can be thought of as the longitude of the map, the Y coordinate as the latitude, and the Theta as the rotation around the origin versus the X axis measured in radians (multiply by 57.296 to get degrees).

The return string of the command is formatted as follows: OK: %7.2lf,%7.2lf,%5.3lf\r, which means that space is reserved for coordinates up to 99999 with centimeter precision and rotations with precision of a thousandth of a radian. An example of a reply is OK: 52.15, 0.81, 1.929\r, denoting an X coordinate of 52.15, a Y coordinate of 0.81, and a rotation of 1.1929 radians.

Get Status - ?S

The possible system states of the robot are listed in Error: Reference source not found.

The first field of the Get Status reply denotes the system state of the robot. During the execution of a mission, the normal state of the robot is 5, meaning the robot is executing a mission.

By querying with the Get Status command, it is possible for example to see if the robot is in emergency mode and for example activate a blinking light on the attached PLC.

Registers

The serial interface offers 200 custom registers. Registers 1-100 are 32 bit integer registers, while registers 101-200 are 64 bit floating point registers. Writing floating point values to integer registers will truncate the values and loose the information found in the value after the decimal point.

For example, the registers can be used for persistent storage of values or interacting with missions.

If you are using the registers for synchronization between the robot and for example a PLC, please note that the mission subsystem of the robot will accept a difference in values of lower than 10-5 as a match due to internal handling of the numbers. This means that if a mission is programmed to wait for a value of 1.000000 in a register, and the value stored by the PLC is 1.0000005, the values are accepted as a match. It is recommended only to use the integer registers 1-100 as synchronization registers.

Web interface for the registers

To allow for further customization, synchronization, and editing, you can use the PLC registers accessible in the robot interface.

Follow the steps below to use PLC registers:

Step 1: In the robot interface, go to System > PLC registers.

Step 2: Select Set register and enter 2 in the Register field and 20 in the Value field. Select OK. The editing window closes, and the value of Register 2 is now 20.

Step 3: Select Edit in register 1. The value in the register field is automatically filled by the system. Enter 10 in the Value field and select Edit. The Edit PLC register dialog box closes, and the value for Register 1 is updated.

Step 4: Query the register values via for example a PLC or a terminal (in this case a PuTTy terminal) to see the register values.

Examples

In this section, a series of examples are listed as inspiration for users of the MiR Serial Interface. The examples should be regarded as demonstrations of the interface only and not as complete in terms of possible feedback to the users, as these examples focus on the communication over the serial interface.

The CLICK PLC C0-00DD1-D and associated programming software from AutomationDirect have been used to illustrate the examples.

Pause/Continue/Abort button

This example pauses, resumes, or aborts the robot during execution of a mission. This could be beneficial if, for example, the robot is entering an area where personnel are operating heavy equipment, and due to the risk of equipment damage, the robot should wait until the personnel have finished before continuing. If the operation of heavy equipment takes too long, the personnel would like to be able to cancel the current mission and reassign the robot to go back to for example a dock to be assigned new missions.

The example can be realized with a PLC with two buttons connected: one for controlling the pause/continue/abort operation, and one for commanding the robot to return to the Dock position after the abort signal has been sent over the Serial Interface.

The operation of the program is as follows:

1. When the StopButton is pressed, a timer starts. If the timer is pressed more than five seconds, the abort signal !X is sent over the serial interface.

2. If the StopButton (X1) is activated, and pause has not been sent, the !P signal is sent over the serial interface.

3. If the StopButton is released, and the abort timer has not fired, the continue signal !C is sent over the serial interface.

4. If the abort signal has been sent, and the DockButton has been pressed, the Go To Position with position Dock is sent !GO:Dock.
   

Using the registers as synchronization between the robot and a PLC

One of the key features of the MiR Serial Interface is the ability to share information between the robot and peripheral devices connected via the MiR Serial Interface, such as PLCs, using one or more of the 200 available registers.

These registers can be assigned values by the PLC and used for triggering events in the robot programming interface to signal when a PLC based process has been completed, and the robot can proceed with its mission.

The procedure of the program is as follows:

1. The robot drives to the specified position.

2. The value of Register 10 is set to 1 to signal the top-mounted PLC to start operation.

3. The robot waits while monitoring the status of Register 10. When the value of the Register is 0, it proceeds to position OffloadPosition.

4. PLC: The subroutine Proc MiR SerialInterface monitors the serial interface, sends periodic commands to get the value of Register 10 (?R#10), and parses the incoming string. The value of Register 10 is put into the register DS1.

5. PLC: If this value is equal to 1, the StartSignal register is activated which in turn activates the (in this case abstract) process of the TopModuleProcess subroutine. This process uses the PLC register C2 to signal when the process is complete.

6. PLC: When the process is complete, and register C2 is enabled, the PLC writes the value ‘0’ to register 10 with the command !R10#0.

7. The robot observes that Register 10 has returned to value 0 and proceeds to the specified position.

Interfacing using PuTTy

The serial interface protocol is a generic protocol whose use extends beyond the realm of PLCs. If the users wish to use it with for example a PC equipped with a RS232 port, it is possible either through custom software or through either commercially available or freeware software from a wide range of vendors and organizations.

An example of such a piece of software is the PuTTy2 client. Originally written with SSH and Telnet clients in mind, the program is also able to handle serial connections in the terminal. Other terminal programs, such as Windows Hyperterminal, Docklight, RealTerm, or similar can also be used. Please note that the PuTTy terminal program does not offer the use of delete or backspace characters in the terminal window, so any commands with spelling errors will not be accepted.

The example will demonstrate how to interact with the Mission subsystem of the robot platform. The example assumes that three missions called Go Home, Dock, and Call Elevator have been created, using the MiR robot interface, and the current mission queue is empty.

To interface using PuTTy, follow the steps below:

Step 1: Download the PuTTy executable from for example http:/the.earth.li/~sgtatham/putty /latest/x86/putty.exe.

Step 2: Open the program with sufficient user privileges.

Step 3: Select Serial.

Step 4: Enter the correct parameters for the serial port in the Serial line and Speed fields. In this case, COM10 and a default speed of 19200 baud.

Step 5: (Optional) Select Terminal in the Category list. Select Implicit LF in every CR to make the terminal put in an extra Line Feed character when a Carriage Return is received. Select Force on in the Local echo field of the Line discipline options block to make the terminal echo user inputs.

Step 6: Select Open. The PuTTy terminal will open.

Step 7: Enter ?ML in the terminal, and press Enter to get the currently available Missions. The MiR robot responds with the Missions. In this case, Go Home, Dock, and Call Elevator.

Step 8: Enter ?MQ in the terminal, and press Enter to get the missions in the queue. The MiR robot responds with an empty list OK:, as there are no missions in the queue at this point.

Step 9: Enter!MA: Go Home to queue the Go Home mission to the mission queue and automatically start the mission. The MiR robot responds with OK: Mission appended.

Step 10: Enter ?MA to view the currently active mission in the mission queue. The MiR robot responds with OK: Go Home.

Step 11: Enter !MA: Dock, and press Enter to append the Dock Mission to the queue. The MiR robot responds with OK: Mission appended

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Step 12: Enter ?MQ to get the mission queue. The MiR robot responds with OK: Go Home,Dock.

Step 13: Enter?MA, and press Enter to get the currently executing mission from the Mission queue. The MiR robot responds with OK: Go Home.

Step 14: Enter  !X, and press Enter to abort the currently running mission. The MiR robot responds with OK: Mission aborted.

Step 15: Enter ?MA, and press Enter to view the currently running mission. The MiR robot responds with OK: Dock as the Go Home mission is aborted.

Step 16: Enter !MC, and press Enter to clear the mission queue. The MiR robot responds with OK: Mission queue cleared.

Step 17: Enter ?MQ, and press Enter to view the mission queue. The MiR robot returns an empty list with the response OK: