For a robotic gripper arm we are designing for factory floor use on very small components, we propose to use electrically activated Shape Memory Alloy (SMA) wire harnesses for actuation.
The device being designed is akin to Pick & Place machines used for circuit assembly, but moves over an aircraft-hanger sized work surface on wheels. It manipulates irregular shaped and porous objects between 0.5 cu.cm and 8 cu.cm each - hence the traditional vacuum P&P mechanism does not appeal. Also, individual objects in the assembly line have varying hardness and weights.
Our design constraints are:
- Ensuring minimal to zero vibration and sound
- Using minimal volume within the mechanism (batteries are at the wheelbase, providing stability, so their weight is not a concern)
- Fine variation of gripper pressure
We believe SMA meets the first two constraints well, but need some guidance on achieving constraint 3, i.e. different levels of pressure of the gripper controlled electronically.
- Can PWM of a current above the activation threshold (320 mA for 0.005 inch Flexinol HT) provide variable, repeatable actuation force?
- Would we need pressure sensors on each fingertip and a closed loop control for grip, or can the gripper be calibrated periodically and maintain repeatable force?
- Is there any well-documented precedent or study we should be referring to?