Speed, Precision. RSA and SMAC recently developed an application to assemble a measured dosage device for medical use. The device is operated by twisting which changes the dosage size. It is made our of plastic and is only the size of a thick and short pen. Part of the assembly is to screw in plastic screws. These screws are rotated counter clockwise to set the threads properly, and then rotated clockwise to set. The height, rotation count and torque are all tested to verify that the screw is set.
This application needs an actuator that has two axes that are independantly controlled. The SMAC LCR series linear rotary actuator is the choice for this application.
The LCR has a linear servo motor moving the head up and down, and a rotary servo motor rotating the head. It also has an air powered grabbing head to grab the screw. The actuator sets the screw in place by rotating counter clockwise until it senses the threads are lined up properly. Then rotates clockwise to fully set the screw. The threading is verified using:
- Oversized / undersized thread
- Number of threads
- Cross thread
- Thread depth
- No thread or dislocated thread
- Pitch measurement
- Shallow / blocked hole
- Increase of torque/gear ratio or higher rotary encoder resolutions are available
The actuator can also measure the final rotational position of the screw to prepare it for subsequent assembly steps. All of this takes place in a device that is only as big as a credit card and 70 mm thick. Given the size of the product, it makes the assembly of a device this size possible. It is also fast, but it won’t damage the parts by overheating or breaking the plastic parts.
The LCR series is also Clean Room compatible and can use FDA approved lube.
Lastly, this application used a ACS Motion controller that can control up to 4 dual axis actuators making set up and maintenance much simpler.