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| Illustration 1 | g06168621 |
The positioning system is built around a Position Computer System (PCS). The PCS uses the input from a wheel speed sensor, GNSS receivers, GNSS corrections, and inertial measurement unit data to produce a high precision position information to the Autonomous Control Modules (Auto ECMs). This data reflects:
- GNSS time
- Global position
- Machine pitch
- Machine roll
- Machine yaw
- A Pulse Per Second (PPS) timing signal used by the autonomous system
The autonomy system continuously compares the PCS high precision position information against other systems to ensure that positioning information is validated before being used. The main check that is performed is a comparison between the PCS position and the GNSS position directly from the GNSS receivers. If the GNSS receiver position accuracy does not meet the autonomy system requirements, the autonomy system will attempt to use Perception Based Localization (PBL) to validate the PCS position.
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| Illustration 2 | g03737122 |
The PCS is connected to three types of input devices that provide information used to calculate high precision positioning data and a timing signal. The input devices are two GNSS antennas that provide signals to internally mounted GNSS receivers, an Inertial Measurement Unit (IMU) and a Transmission Output Speed (TOS) sensor. The TOS is used for ground speed information.
The PCS receives control commands from and communicates with Auto ECM #1 over RS232 data lines. These data lines can be found at PCS ports sensor 1, sensor 2, and Comm. The PCS also communicates with the autonomous system using the LAN Ethernet 1, connected to the PCS module port "Ethernet".
The timing signal is communicated to the pulse per second system (PPS) buffer using TTL logic data lines. These data lines can be found at PCS module port "Sensor 1", pins 12 and 14.
Primary and Secondary GNSS Antenna
Two GNSS antenna, mounted to the front of the truck, provide GNSS satellite signals directly to the GNSS receivers located within the PCS module. An unobstructed line of sight to four or more GNSS satellites is required for the antennas. The antennas, identified as primary and secondary, connect to the PCS module at port "A 1" and "A 2".
Inertial Measurement Units (IMU)
The Autonomy Inertial Measurement Unit (IMU) is at the front of truck near top center of radiator. The autonomy IMU is connected to the PCS module at port IMU, pins 1-19.
The IMU measures movement in 6 degrees of freedom by measuring acceleration along three axes of the truck and angular rate about each axis. This information is used by the PCS to calculate position.
The ABS rear inertial measurement unit (IMU) is on top of the rear axle housing. The ABS IMU connects to the Brake ECM using the Auto CAN data link.
The IMU measures movement in 4 degrees of freedom by measuring acceleration along three axes of the truck. The ABS IMU also measures the angular rate about one axis depending on mounting position. The autonomy system uses this input to measure the machine yaw rate.
Transmission Output Speed Sensor
The transmission output speed sensor (TOS) is located inside the rear axle. The sensor produces both a high-resolution speed signal used by the autonomous system and a low-resolution signal used by the Powertrain ECM. This output feeds through a hardware filter in the autonomy cabinet and then into the PCS module at port DMI.
The high-resolution speed signal output is used by the PCS to measure the truck ground speed and forward or reverse direction. The TOS sensor is used at low speeds when GPS speed is less reliable.
GNSS corrections are positioning messages received by the truck from the base station. The GNSS receiver on the AMT uses these messages to correct and fix the position the truck is reporting down to the centimeter level. Corrections are received by the radio which are then transmitted over to router and then sent to Auto ECM #1. Auto ECM #1 distributes the corrections data to the positioning module on the AMT.
Perception-based localization (PBL) is a system that uses designated targets at defined locations to determine a position. This position is used as a validation check by the PCS position. The placement of PBL targets in areas of low GNSS coverage provide the AMT with an alternate method to determine an accurate position. This system is used only in situations where the GNSS receiver position accuracy does not meet autonomy requirements.
PBL targets are typically cylindrical, reflective, rigid, and upright objects set at designated intervals and registered on the mine model (Cat® MineStar System).