MIR 250 Technical Manual
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MIR 250 Technical Manual

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Technical Guide (en)
Date: 07/2020
Revision: v.1.0

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  • Page 1 Technical Guide (en) Date: 07/2020 Revision: v.1.0...
  • Page 2 All rights reserved. No parts of this manual may be reproduced in any form without the express written permission of Mobile Industrial Robots A/S (MiR). MiR makes no warranties, expressed or implied, in respect of this document or its contents. In addition, the contents of the document are subject to change without prior notice.

  • Page 3: Table Of Contents

    Table of contents 1. About this document 2. Robot sub-systems 2.1 Navigation and control system 2.2 Safety system 2.3 Motor and brake control system 3. Robot components 3.1 Safety laser scanners 3.2 3D cameras 3.3 Proximity sensor modules and indicator lights 3.4 Drive train 3.5 Power board 3.6 Safety contactors...

  • Page 4: About This Document

    1. About this document 1. About this document This document describes the components, sub-systems, and connections in the MiR250 robot, providing an overview of how the robot works. This guide is intended to be used to provide additional information regarding how MiR250 robots and their key components work.

  • Page 5: Robot Sub-Systems

    2. Robot sub-systems 2. Robot sub-systems The following sections describe these robot sub-systems: • The navigation and control system determines the path the robot should follow to reach its goal destination. • The safety system monitors the robot's components and surroundings through several functions and brings the robot to a stop if an unsafe situation occurs.
  • Page 6 2. Robot sub-systems • Motor controller, motors, and brakes The motor controller determines how much power each motor must receive to drive the robot along the intended path safely. Once the robot reaches the goal position, the brakes are engaged to stop the robot. Each part of the process is described in greater detail in the following sections.
  • Page 7 2. Robot sub-systems User input To enable the robot to navigate autonomously, you must provide the following: • A map of the area, either from a .png file or created with the robot using the mapping function. • A goal destination on that map. •...
  • Page 8 2. Robot sub-systems Figure 2.3. The global path is shown with the blue dotted line that leads from the start to the goal position. The global path is created only at the start of a move action or if the robot has failed to reach the goal position and needs to create a new path.
  • Page 9 2. Robot sub-systems Local planner The local planner is used continuously while the robot is driving to guide it around obstacles while still following the global path. Figure 2.5. The global path is indicated with the dotted blue line. The local path is indicated with the blue arrow, showing the robot driving around a dynamic obstacle.
  • Page 10 2. Robot sub-systems Figure 2.6. The local planner usually follows the global planner, but as soon as an obstacle gets in the way, the local planner determines which immediate path will get the robot around the obstacle. In this case, it will likely choose the path indicated with a green arrow.
  • Page 11 2. Robot sub-systems What the laser scanners What a human sees What the 3D cameras see A chair placed in the In the robot interface, the The 3D cameras detect corner of a room is red lines on a map are more details of the chair detectable by the robot.
  • Page 12 2. Robot sub-systems When in motion, the safety laser scanners continuously scan the surroundings to detect objects. Figure 2.7. The two safety laser scanners together provide a full 360° view around the robot. The laser scanners have the following limitations: •...
  • Page 13 Vertically up to 1800 mm at a distance of 1200 mm in front of the robot. • Horizontally in an angle of 114° and 250 mm to the first view of ground. The 3D cameras are only used for navigation. They are not part of the robot's safety system.
  • Page 14 2. Robot sub-systems Figure 2.8. The two 3D cameras can see objects up to 1800 mm above floor height at a distance of 1200 mm in front of the robot and have a horizontal field of view of 114°. The 3D cameras have the following limitations: •...
  • Page 15 2. Robot sub-systems repetitive patterns. • The cameras may detect phantom obstacles if they are exposed to strong direct light. Proximity sensors Proximity sensors placed in all four corners of the robot detect objects close to the floor that cannot be detected by the safety laser scanners. Using infrared light, the proximity sensors point downwards and make sure that the robot does not run into low objects, such as pallets and forklift forks.
  • Page 16 2. Robot sub-systems Localization The goal of the localization process is for the robot to determine where it is currently located on its map. The robot has three inputs for determining where it is: • The initial position of the robot. This is used as a reference point for the methods used to determine the robot position.
  • Page 17 2. Robot sub-systems computer only compares with the area where it expects the robot to be based on the encoder and IMU data. This means it is important that the initial position of the robot is correct. The robot computer uses the comparison and the odometry data from the encoders and IMU to produce a number of points where the robot is most likely to be.
  • Page 18 2. Robot sub-systems No distinguishable landmarks Many distinguishing landmarks • The robot must be able to detect the static landmarks that are marked on the map to be able to approximate its current position. Make sure there are not too many dynamic obstacles around the robot so that it cannot detect any static landmarks.
  • Page 19 2. Robot sub-systems • To improve the robot's localization, it can often help to divide long continuous walls on the map. Even if the walls are connected in the actual work environment, it can help the localization process if the walls on the map are divided into smaller sections. Undivided walls Divided walls •...
  • Page 20 2. Robot sub-systems The motor controller translates the difference into the amount of power that must be sent to each motor to achieve the desired velocity. The motor controller regulates whether the amount of power sent to the motors is resulting in the correct velocity by translating the motor encoder data into the robot's velocity and comparing this to the desired velocity—see Motor and brake control system on page 39.
  • Page 21 2. Robot sub-systems The mechanical brakes are only used to stop the robot when in motion in emergency situations triggered by the safety system. The mechanical brakes are automatically released again when the robot receives a new order requiring it to move. Common issues •...

  • Page 22: Safety System

    2. Robot sub-systems • Encoder stall and skid detection errors This error is not directly related to navigation, but occurs whenever the robot registers that it is not moving as expected based on encoder data. • Stall errors occur if the power is delivered to the robot but it doesn't move. This can occur if something is physically blocking the robot.
  • Page 23 2. Robot sub-systems Types of stop There are four different stopped states: • Operational stop • Protective stop • Emergency stop • Manual stop The last three types of stop are monitored by the safety PLC. Operational stop The robot is in Operational stop when it is stopped through the robot interface either through a mission action or by pausing the mission.
  • Page 24 2. Robot sub-systems • The safety system detects a fault, or the motor control system detects a discrepancy To bring the robot out of Protective stop, resolve the fault causing the error. Use information regarding the error from the robot interface to determine the fault. For further guidance, see the troubleshooting guides on the Distributor site.
  • Page 25 2. Robot sub-systems CAUTION Emergency stop buttons are not designed for frequent use. If a button has been used too many times, it may fail to stop the robot in an emergency situation, and nearby personnel may be injured by electrical hazards or collision with moving parts.
  • Page 26 2. Robot sub-systems brought to a stop. The function determines the speed of the two drive wheels using motor encoder data and switches between predefined protective fields accordingly. The faster the speed, the larger the protective field is. • Overspeed avoidance The safety system monitors if the motor encoder data indicates that the speed of each motor is above the limits for maximum rated speed.
  • Page 27 The reduced speed function can be connected to a top module, enabling it to make the robot reduce its speed to 0.3 m/s. This is for example used by MiR lifts to ensure that the robot does not drive fast when the lift is raised.
  • Page 28 2. Robot sub-systems Collision avoidance The collision avoidance function prevents the robot from colliding with personnel or obstacles by stopping it before it collides with any detected obstacles. It does this using the safety laser scanners. Drives when the area is clear Stops when an obstacle is detected Figure 2.13.
  • Page 29 2. Robot sub-systems WARNING The protective field sets are configured to comply with the safety standards of MiR250. Modifications may prevent the robot from stopping in time to avoid collision with personnel and equipment. Any modifications of the configuration file in the safety software will void the CE mark and compliance to all safety standards listed in the specification of the application and in other way declared.
  • Page 30 2. Robot sub-systems Field set when driving forward The following table shows the range of the protective fields when the robot is driving forward. The table describes the length of the field in front of the robot in different cases. Each case is defined by a speed interval that the robot may operate at.
  • Page 31 2. Robot sub-systems Field set when driving backward The field set for driving backward is the same as the field set for driving forward. However, the robot is limited to a top speed of 1.0 m/s when driving backward and therefor only have five fields.
  • Page 32 2. Robot sub-systems Field sets to the sides The field sets on each side of MiR250 Dynamic varies with the speed of the robot. At speeds below 0.5 m/s, the field sets are very small, making it possible for the robot to traverse narrower corridors.
  • Page 33 2. Robot sub-systems • Reduces the size of the field sets • Turns off Collision detection • Decreases the speed • Flashes the yellow signal lights You can also mute the personnel detection means using the robot interface: Put the robot into Manual mode. In the robot interface, select Muted personnel detection means in the joystick control.
  • Page 34 2. Robot sub-systems It is intended that the circuit is set up so the 24 V signal delivered from the safety PLC outputs passes through all Emergency stop buttons of the top module and then continues to the two input pins. When the input pins both receive 24 V, the robot can operate. The connected Emergency stop buttons must break the circuit when you press them so both inputs receive a 0 V signal that will bring the robot into Emergency stop.
  • Page 35 2. Robot sub-systems Protective stop. The robot can be brought out of Protective stop again if both pins receive 24 V again. If the pins are unequally set for more than three seconds, the safety PLC registers this as an error in the system and needs to be reset before the robot can operate again. To do this, you must restart the robot.
  • Page 36 2. Robot sub-systems Signal when driving Signal when stopped Figure 2.18. When the robot is driving, the safety PLC sends a 0 V signal to the top module through the Auxiliary safety function interface. When the robot is stopped, the signal becomes 24 V. Pins 5 in interfaces A and B of the Auxiliary safety functions are used for the Locomotion function.
  • Page 37 2. Robot sub-systems Shared emergency stop Shared emergency stop Not in Emergency stop inputs are 0 V inputs are unequal Figure 2.19. There are three cases described above. Respectively, they illustrate: 1. the robot is not in Emergency stop so the output is 24 V, 2. the robot is in Emergency stop because it receives 0 V input from the Shared emergency stop interface, 3.
  • Page 38 2. Robot sub-systems Default speed Reduced speed Reduced speed Figure 2.20. The robot drives at its default speed only when both inputs are 24 V. If either or both pins are 0 V, the robot drives at 0.3 m/s. Pins 4 in interfaces A and B of the Auxiliary safety functions are used for the Reduced speed function.

  • Page 39: Motor And Brake Control System

    2. Robot sub-systems 2.3 Motor and brake control system The motor and brake control system is responsible for driving the robot. The robot computer translates the global and local paths into velocity and acceleration instructions that it sends to the motor controller. The motor controller then derives how much power needs to be sent to the motors to reach the correct velocity.
  • Page 40 2. Robot sub-systems Figure 2.21. Diagram of the motor and brake control system. The blue arrows indicate data or signal connections, the green arrows indicate power connections. Components with a red outline are part of the safety system, blue components are part of the control system, and green components are part of the power system.
  • Page 41 2. Robot sub-systems Figure 2.22. A simplified diagram of the motor control loop for one motor. The process that occurs in the control loop is described with the following steps: The robot computer determines the path that the robot must drive and what the desired rotational speed for each motor must be for the robot to drive the intended path.
  • Page 42 2. Robot sub-systems The robot computer sends this information to the motor controller. The motor controller translates the desired speed into how much current each motor must receive to achieve the desired speed. Forward Right turn Left turn Pivot Figure 2.23. When both motors rotate at the same speed, the robot drives straight. When the motor on the right rotates faster, the robot turns to the left, and vice versa for the left motor.
  • Page 43 2. Robot sub-systems As the robot drives, the motor controller receives feedback from the motor encoders. The motor controller determines how far the actual motor speed is from the desired speed. The resulting value is known as the speed error. The motor controller uses the error to try to correct the amount of current that should be sent to the motor.
  • Page 44 2. Robot sub-systems The safety PLC controls the mechanical brakes using the brake relay. To engage the brakes, the safety PLC turns the relay off to cut the power to the brakes. It is also possible to override the signal from the safety PLC using the Manual brake release switch. When the Manual brake release switch is turned on, the brakes are released, and the safety PLC receives a status signal from the switch.

  • Page 45: Robot Components

    3. Robot components 3. Robot components Once you have determined which component on your robot may be failing, you may need to understand the component itself to further troubleshoot the issue. This section describes the various robot components in more detail, enabling you to troubleshoot the exact issue you are experiencing with a component.
  • Page 46 3. Robot components • Guidance The robot detects obstacles with the laser scanners so it can maneuver around anything in its path and continue to its goal. Location and connection The laser scanners are located in the front-left corner and rear-right corner of the robot. The scanners send data to both the safety PLC and the robot computer.
  • Page 47 3. Robot components How it works Figure 3.1 illustrates the working principle of the safety laser scanner. In the illustration, the laser scanner (1) constantly emits laser pulses (2) through the optics cover. When the laser pulse hits an opaque object (3), the laser pulse is reflected (4) back through the scanner's optics cover, and its return is detected by the scanner.
  • Page 48 With MiR robots you can also see at what point the laser scanners are currently detecting objects. Under Monitoring > Safety system, a visualization of the MiR robot is displayed—...
  • Page 49 3. Robot components Figure 3.2. In the robot interface, you can see a visualization of what the safety lasers scanners are detecting around the robot. Common issues • The data collected from the laser scanners is incorrect and is interfering with how the robot operates There are often a few data points from the laser scanners that are incorrect.

  • Page 50: Cameras

    3. Robot components • The robot cannot localize because it is not receiving data from the laser scanners If the robot cannot connect to the scanners, check whether the scanners are receiving power by removing the corner shield and verifying that the status LED on the scanner is lit.
  • Page 51 3. Robot components They connect directly to the robot computer via USB cables that both power the cameras and retrieve data. How it works A 3D camera consists of two displaced cameras that use active infrared stereo vision to create a point cloud describing the depth of detected objects—see Obstacle detection on MiR250 Technical Guide (en) 07/2020 - v.1.0 ©Copyright 2020: Mobile Industrial Robots A/S.
  • Page 52 3. Robot components page 10 for an example. Figure 3.3. Illustration of how active infrared stereo vision works. Infrared light emitted from the camera (1) is reflected off of objects in front of the camera (2). Each wave of infrared light directed back at the cameras (4) are detected and used to create an image.
  • Page 53 3. Robot components Image from left camera Image from right camera Overlapped images Figure 3.4. The above images illustrate how objects that are further from the camera have a smaller displacement in the two images than objects closer to the camera. Common issues •...

  • Page 54: Proximity Sensor Modules And Indicator Lights

    3. Robot components 3.3 Proximity sensor modules and indicator lights The proximity sensor modules consist of a circuit board and three infrared proximity sensors. The indicator lights are controlled by the circuit boards within each proximity sensor module. For this reason, although their purposes are different, they are explained in the same section of this guide.
  • Page 55 3. Robot components Location and connection The proximity boards and indicator lights connect in a single CAN bus circuit that starts at the power board and runs through each proximity board to the indicator lights. Figure 3.5. The CAN bus begins at the power board and connects to a PCBA board where the connection splits to the motor controller carrier board.
  • Page 56 3. Robot components • A status light connector • A signal light connector. The proximity boards are connected together through the CAN bus inputs and outputs: each signal light is connected to one proximity board, and the status light LED bands are connected to every second proximity board, starting with the first one.
  • Page 57 3. Robot components Indicator lights The indicator lights change based on the robot's status and the intended driving direction, which are determined by the robot computer. The robot computer relays the information to the power board, which then sends the information through the CAN bus connection to the circuit boards.
  • Page 58 3. Robot components Common issues • Faulty or desynchronized lights If only one light does not work, it is likely the light or the connection to the light is faulty. If multiple consecutive lights are disconnected, one of the proximity boards is likely faulty or disconnected.

  • Page 59: Drive Train

    3. Robot components 3.4 Drive train There are two drive trains in the robot; one on each side. Each drive train consists of a drive wheel, a motor, a mechanical brake, a gear box, and two motor encoders (one for the safety system and one for the control system). The drive train contains the components used to make the robot move.
  • Page 60 3. Robot components The motor and the controller encoder are connected to the motor controller carrier board, the safety encoder is connected to the safety PLC, and the mechanical brake is connected to the motor controller carrier board via the mechanical brake relay controlled by the Manual brake release switch.
  • Page 61 3. Robot components The rotor is the center piece in the motor that rotates. It has two magnetic poles. The stator is the surrounding frame containing the following two components to make the rotor rotate: • Electric coils Coils are mounted to the stator. Electric current travels through the coils to create magnetic fields.
  • Page 62 3. Robot components Dynamic brake function The coils are both used to rotate the rotor and to slow it down when current is no longer passing through them. This is known as the dynamic brake function. It is initiated by switching the SS1 relays so power is no longer delivered to coils but instead absorbs the remaining rotational energy in the rotor.
  • Page 63 3. Robot components Released brakes Engaged brakes Figure 3.7. When the brakes (1) receive 48 V, they are released, and the motor (4) can rotate the gears (3) so the drive wheel (2) can move the robot forward. When the brakes do not receive enough power, they engage to stop the motor from rotating the gears.

  • Page 64: Power Board

    3. Robot components worthwhile to investigate the cables. The error can also be a symptom of other faults in the motor and brake system, so after checking the encoder and hall sensor cables, inspect all other cables connecting the motor controller carrier board to the drive train. •...
  • Page 65 3. Robot components The power board powers all electrical components in the robot. Figure 3.8 shows which components the power board directly provides power to, and through which components it indirectly powers the remaining components. MiR250 Technical Guide (en) 07/2020 - v.1.0 ©Copyright 2020: Mobile Industrial Robots A/S.

  • Page 66: Safety Contactors

    3. Robot components Figure 3.8. Overview of how power is delivered to the main robot components. How it works The power board has several power supply units within it to ensure that it can supply the correct amount of voltage and current to various robot components. The power board is a closed component;...
  • Page 67 3. Robot components Location and connection There are two pairs of contactors in MiR250: the STO contactors and the SS1 contactors. The STO contactors are located next to each other on the left side of the robot. The SS1 contactors are placed near the front on both sides of the robot. The STO contactors are connected to the motor controller carrier board.
  • Page 68 3. Robot components either pulls or pushes the switches so the contacts are connected. When the coil does not receive current, the switches return to a default position where the contacts are not connected and current cannot pass through. Contactor off Contactor on Figure 3.9.
  • Page 69 3. Robot components There are two STO contactors located next to each other. They are connected in series to ensure redundancy in the safety system, meaning that if one of the STO contactor fails to switch to an inactive state, the other contactor works as a backup to cut the power connection.

  • Page 70: Robot Computer

    MiR Fleet, for calculating global and local paths for the robot to follow based on sensor data and user input, and for distributing data correctly to other robot components.
  • Page 71 How it works The robot computer runs a Linux system where MiR's software package is installed. MiR's software is created on a ROS framework, consisting of various nodes for different software tasks. When the robot is turned on, the robot computer immediately begins running the necessary nodes to start up the robot components correctly.

  • Page 72: Safety Plc

    How to USB restore MiR100/MiR200 or How to USB restore MiR500/MiR1000. If your robot has important data that has not been saved to other robots or MiR Fleet, contact Technical Support for assistance in retrieving the data before USB restoring. 3.8 Safety PLC The safety PLC monitors and processes several inputs and outputs to ensure that the robot is only running when it is in a safe state.
  • Page 73 CPU module The CPU module contains the processing unit where the MiR safety software runs. The software dictates the output signals from the safety PLC based on the input signals. MiR250 Technical Guide (en) 07/2020 - v.1.0 ©Copyright 2020: Mobile Industrial Robots A/S.
  • Page 74 3. Robot components Input and output modules In this case, the safety PLC is connected to several I/O circuits that connect to the top module GPIO interface that can either send 24 V or 0 V to indicate either an active or inactive signal respectively. Certain signals result in the robot entering Protective or Emergency stop.
  • Page 75 3. Robot components Signal Circuit description Triggers name Locomotion Connects to pin 5 in the Auxiliary safety function interface B. Output for Locomotion function. Shared E- Connects to pin 6 in the Auxiliary safety function stop out 1 interface A. Output for Shared emergency stop function.

  • Page 76: Router And Access Point

    3. Robot components 3.9 Router and access point The router enables communication through Ethernet between various robot components and also contains a wireless access point that users can use to connect to the robot interface and robot components wirelessly. Location and connection The router is located on the right side of the robot.
  • Page 77 The two antennas on top of the robot connect directly to the robot computer. The antennas are used to connect the robot to an external wireless network, enabling the MiR robot to communicate with other devices connected to the same network.
  • Page 78 3. Robot components The antennas translate electrical signals from the robot components into electromagnetic waves that propagate through the air and are measured and translated back into electrical signals by another antenna and access point. Figure 3.10. When the area between a robot and an access point is clear, the connection is better. If the electromagnetic waves are blocked, the data cannot be picked up by the receiving antenna.
  • Page 79 We have collected many of the best practices you can apply to improve your wireless network in the MiR Network and WiFi Guide which can be found on the MiR website with the manuals for our robots and MiR Fleet.

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