The Rikishi Electronics Unit (REU) is a Robotic Arm Controller designed to drive up to nine separate servo motors (joints), such as found on robotic arms or articulated structures.
The Rikishi Electronics Unit (REU) provides a platform for command and telemetry processing, execution of motor control commands and algorithms, execution of general purpose commands, and storage for volatile and nonvolatiledata.
The REU is composed of (1) communication board (COMM) and (9) motor controller boards (MCBs) integrated into a 10 slot 3U chassis. Spacecraft bus power (28 VDC) is applied directly to the REU backplane via its rear 8-pin power
connector. There are chassis mounted DC/DC converters that provide regulated power from the 28 VDC spacecraft bus.
The spacecraft communicates to the REU via RS-422. An ‘emergency disable’ and ‘emergency hold’ discrete input is provided via the COMM board. The REU is designed as a single-string system without explicit redundancy. The (1)
COMM board and the (9) MCBs are all on the primary side of the 28 VDC spacecraft bus. The COMM board provides isolated 5 V power required to power the COMM devices that are on the secondary side.
To move the Robotic Arm, joint level commands are sent to the COMM board from the S/C at a 500Hz rate. Each command contains the position, velocity, gravity compensation, and inertial load compensation values for each of the motors. If the command is accepted by the COMM board, it will forward the command to the appropriate MCB board for execution by the low level PID controller.
Position/velocity telemetry data is returned at a 500Hz rate from the COMM board to the S/C. Telemetry contains raw R/D position/velocity data and status from each of the MCB boards.
Commands can also be sent on the secondary command link to control such things as setting PID controller parameters, setting/clearing fault masks, clearing failures, writing/dumping SRAM, writing/dumping EEPROM, dumping
debug parameters, etc. This secondary command link is setup for a command & acknowledge interface. All required telemetry not returned in 500Hz telemetry is returned using this interface.
Servo Controller Board Features
- BRE ‘SNAP’ DSP Controller in FPGA (20 MFLOPS)
- Command and telemetry interface
- Resolver drive (differential sine wave)
- Motor drive (10 A 3-phase servo motor outputs)
- Motor commutation
- Motor brake drive and control (Opto-Isolated)
- Actuator output position determination
- Actuator output position closed loop control
- Analog data measurement
- Non-volatile code storage
- Typical Mass, Power, Dimensions
- Volatile SRAM storage for micro-controller code
- PRT current source and measurement
- Pre-amp +/-15 V supply (Opto-Isolated)
- EMI filtered power for 28 VDC 3-phase outputs (10 A)
Typical Mass, Power, Dimensions
- 9-Joint REU
- <10 kg
- 290 mm x 190 mm x 120 mm
- Peak: 190 W Average: 100 W (3 Joints @ 3 A, 3 Joints @ 5 A, 3 Joints @ 10 A)
- Motor Controller Board
- <500 grams
- 3U Form Factor
- 10 A Motor Driver Capability