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Abstract
This design may be thought of as a direct descendant of the Spring 2007 design with refined constraints and a sensing mechanism. This actuator was sent out for manufacturing and has been assembled by the team and is currently being tested.
Sensor Design
For sensing, the actuator uses an Austrian Microsystems AS5046 magnetic rotary encoder to sense simultaneously the linear position of the the shaft and the rotational position. From these, it infers the torque of the output shaft and the rotational position of the output shaft. In prototype, the design used the adapter board made by the chip manufacturer to avoid waiting for custom electronics in the sensor design.
Problems encountered
A spur gear train allows for the motor to spin much faster than the shaft which is axially compliant, allowing bearings to be used on the shaft without the having to move axially; however, the spur gears introduce inefficiency and backlash to the system.
The magnetic sensor has 8 bits of precision for sensing magnetic field strength; however, this is probably insufficient granularity to do very good force control, especially since the field strength does not drop off linearly with distance and therefore some of the linear range of motion has higher precision than the rest.
Testing
Current status: Operational with AS5045 rotary encoder, still in progress with AS5046 and therefore the current actuator design does not have force-sensing capabilities.
Copyright Notice
The contents of this page are Copyright © 2007 Matthew Aasted, Guilherme Cavalcanti, Jeffrey DeCew, Christopher Dellin, Gill Pratt, Kevin Sihlanick, and Jon Tse.