Case study

Challenge

• A mass producible, highly cost-effective, miniature linear actuator with absolute positional feedback.
• The linear actuator had to be able to produce 0.25N of dynamic force, and would be used to open and close the grabbing jaws built into the front of each robot.
• Constrained by an awkward securing footprint from a much more expensive supplier’s actuator.

Solution

• Our team developed an actuator and based the design around a 7mm coreless 3v motor, with a custom D-shaft to take the pinion gear.
• Further gearing was added to amplify torque and a custom-lead screw was manufactured.
• The chassis, output arm, and pinion gears were injection moulded in engineering plastics.
• We added a very cost effective absolute positional feedback mechanism and integrated it into the chassis PCB.

Results

• Positional feedback was a real challenge, but accomplished elegantly and reliably.
• Developed an innovative solution and created an end-of-line testing station to validate and serialise each unit.
• Precision Microdrives’ testing infrastructure allowed us to assure our customer that their manufacturing risk was manged throughout.
• Every production batch was delivered on time and to spec. 

STAGE 1

Designing for application

• The application required us to push / pull a 1mm shaft and there was a requirement for manual adjustment / alignment during the final robot assembly.
• We developed our application-specific actuator in Solidworks, and based the design around a 7mm coreless 3v motor, with a custom D-shaft to take the pinion gear.
• The chassis, output arm, and pinion gears were injection moulded in engineering plastics.
• The lead-screw was based on a M2 thread, and further machined to produce a trapezoid profile to prevent sticking when higher forces were applied.
• The lead-screw was supported by miniature sintered bearings at either end of the chassis.

STAGE 2

Design for manufacture

• To offer absolute positional feedback in this package and budget, was a real challenge.
• We solved this by creating a linear potentiometer on the PCB, which also acted as a mounting base for the injection moulded frame.
• Almost half of the project hours were devoted to performing detailed DFM to reduce part-count and manufacturing costs.
• Detailed planning, lifecycle management and statistical controls allowed us to work hand-in-hand with the customer to develop – plan – produce and manufacture. 

STAGE 3

Precision performance

• We also designed a driving algorithm for our customer to implement in their motion control software. This prevented lead-screw lockup.
• On the line we built an end-of-line testing station to 100% test, characterise and serialise each device for positional calibration.
• PMD’s testing infrastructure allowed us to assure our customer that the product was validated and we managing their manufacturing risk throughout.
• Every production batch was delivered on time and to spec.