Building a Magnetic Track Guided AGV Application Note AN1326 AGV Photo courtesy of Artisteril SA. Barcelona. Spain An automated guided vehicle (AGV) can be built with as little as two Roboteq components: An MGS1600C magnetic guide sensor, and one of the many dual channel motor controllers available in Roboteq’s catalog. This application note will use a Roboteq MDC2260 dual channel controller, however the techniques described are identical for all other controller models.
Building a Magnetic Track Guided AGV AN12345 information to the motor controller which will then adjust the steering so that the vehicle remains at the center of the track. Magnetic markers positioned on the left and right side of the track give the AGV location information that will be used to make stop and fork left/right decisions. Benefits of Magnetic Track Guiding Magnetic tapes are one of several line-following techniques. The other 2 main techniques are induction wire guide, and optical.
Building a Magnetic Track Guided AGV Design 4Wheel Drive Center Drive & Casters Steerable Drive Motor Rear Drive and Rack Steering Simplicity Simplest Simple Medium Complex Steering Coarse Precise Very Precise Precise AN12345 Reversible Yes Yes No Difficult in reverse Sensor Mount The sensor should be placed as shown in the above diagrams for each chassis design. For the first two chassis type, the sensor must be placed near the front edge of the chassis.
Building a Magnetic Track Guided AGV MGS1600C Sensor Front Right Motor AN12345 Rear Right Motor Push Button Roboteq Motor Controller Digital In 2 5V Out M1+ M1On Off Pwr Ctrl GND GND Pulse In 1 VMot + M2+ M2- - Battery Rear Left Motor Front Left Motor The figure below shows how the detailed connections to the controller’s connector. This wiring is compatible with all Roboteq controllers equipped with a 15-pin DSub connector.
Building a Magnetic Track Guided AGV AN12345 For configuration, monitoring and troubleshooting, connect the sensor to the PC via the USB connector located under the screw plug. Run the Magsensor PC utility to change the tape width if using a 50mm tape, or use the waveform display view to monitor the shape of the magnetic field. With no tape present, the PC utility must show a nearly flat line. For best results, always perform a zero calibration when operating the sensor in a new environment.
Building a Magnetic Track Guided AGV AN12345 Motor Controller Configuration To received and recognize data from the sensor the controller must first be connected to a PC running the Roborun+ PC utility. In the configuration menu, the pulse input that is connected to the sensor must be enabled and configured as “Magsensor”. Next, the controller must be configured to operate in mixed mode so that the a steering command will apply a different amount of power to the left and right motor for making turns.
Building a Magnetic Track Guided AGV AN12345 Steering Control The sensor outputs a value that is the tape’s distance from the center of the track. This information is then used to correct the steering. If the tape is centered, the value is 0 and no steering correction is needed. The further the track is from the center, in one or the other direction, the stronger the steering change. In this article, a Proportional control is implemented.
Building a Magnetic Track Guided AGV AN12345 In this application, we will use markers on the left or right side to indicate which track to follow at a fork. Markers located both at the left and right side will indicate a stop location. More elaborate marker arrangement can be made to carry more information about a location on the track. An example of multi-level markers is provided further in the application note.
Building a Magnetic Track Guided AGV AN12345 Stop Markers Charging Fork Markers Loading1 Merge Markers Fork Left Merge Left Merge Right Loading Loading Unloading Fork Right Init Constants Read Sensor Read Button Button Pressed? Y Clear Pause Timer N N Throttle = 0 Timer=0 & Tape Detected 1 Marker Present Y Throttle = 50% Y Select Left or Right Track N 2 Markers Presents Y Load 30s in Pause Timer N Steering = Track Position * Gain Apply Steering and Throttle November 26, 2013 Pa
Building a Magnetic Track Guided AGV AN12345 Setup and Troubleshooting Manually Test Drive the AGV Before the sensor can be used for automatic steering, it is a good idea to test drive the chassis manually, either by attaching a joystick to the PC that is connected to the motor controller, or by using an RC radio. If the vehicle is difficult to drive manually, in automatic mode it will be equally challenging.
Building a Magnetic Track Guided AGV AN12345 The amount of correction can also be capped to avoid over steering. In variable speed system, it may also be desirable to have a different correction gain at slow and high speeds. Using Multi-Level Markers In this application example, we used a simple left and right marker pair to identify a stop location. In typical applications more information is needed about location so that the AGV will change its behavior.
Building a Magnetic Track Guided AGV AN12345 Improving Stop Position Accuracy In applications requiring the AGV to stop at a very precise location, a secondary sensor, oriented at 90o from the main sensor, can be added. This sensor can then be used to locate another magnetic guide with a 1mm position accuracy. The figure below shows the sensors and guides arrangements.
Building a Magnetic Track Guided AGV dim dim dim dim dim dim dim dim dim dim AN12345 MarkerLeft as boolean MarkerRight as boolean Throttle as integer Tape_Position as integer LineSelect as integer Steering as integer GoButton as boolean RunState as boolean NotOnStopMarker as boolean PauseTime as integer ' initialize constants Gain = -7 ' Use negative value to invert steering command DefaultThrottle = 250 ' Motor power level while the AGV runs LineSelect = 1 ' Use left track by default PauseTime = 30000
