The BarrettHand consists its central supervisory microprocessor that coordinates four dedicated motion-control microprocessors and controls I/O via the RS232 line inside its compact palm. The control electronics are created on a parallel 70-pin backplane bus. Associated with each motion-control microprocessor are the related motor commutation electronics, sensor electronics, and motor-power current-amplifier electronics for that finger or spread action. The microprocessor of supervisory directs I/O communication via a high-speed, industry-standard RS232 serial communications link to the work cell PC or controller. RS232 offers compatibility with any robot controller while limiting umbilical cable diameter for all communications and power to only 8mm. The published grasper communications language (GSL) optimizes communications speed, exploiting the difference between bandwidth and time-of-flight latency for the special case of graspers. It is important to recognize that graspers usually remain inactive during most of the work cell cycle, while the arm is performing its gross motions, and are only active for short bursts at the ends of an arm’s trajectories.
While the robotic arm knees high control bandwidth during the entire cycle, the grasper has plenty of time to receive a large amount of setup information as it approaches its target. Then, the work cell controller releases a “trigger” command with precision timing, such as the ASCII character “C” for close, which begins grasp execution within a couple milliseconds.
The grasper can accept commands and communicate from any robot-workcell controller, PC, UNIX box, Mac, or even a Palmpilot via standard ASCII RS232-C serial communication — the common denominator of communications protocols. Though robust, RS232 has a slow bandwidth compared to FireWire standards or USB, but its simplicity leads to small latencies for short bursts of data. It has achieved time of flight to acknowledge and execute a command (from the work cell controller to the grasper and then back again to the work cell controller) of the order of milliseconds by streamlining the GCL.
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