05/29/2022
This is a small dial machine we completed. The main design parameters were,
1. Replace all pneumatic actuators with electric servo actuators.
2. Cycle time of 3 seconds
The justification for converting to electric actuators had two main points. The first being versatility and control of the actuator. In many comparisons between pneumatic and electric actuators, the electric actuator will complete its move before the pneumatic. An example of this can be seen here,
Air Cylinder VS ROBO Cylinder (IAI's Electric Actuator can control vibration of work item.)
The second justification being the reduced load on the compressed air system and the elimination of the maintenance required by pneumatic actuators.
Electric actuators allow us to have tighter control on when a motion starts, stops, and the velocity during the motion. We can control distance traveled and force with far greater precision than with pneumatics. The force control is vital when working with a plastic part that is holding a fluid. If the plastic is cracked or broken, the fluid can spill creating machine downtime. Each actuator that comes in contact with the plastic shell can be limited as to its force output thus insuring the shell is not broken. A part that is mis-aligned will stop the actuator and eventually trip a watchdog timer to return the actuator to its start position and set the part status to reject.
With pneumatic actuators you can control pressure to the actuator to limit its force output, but that typically increases cycle time. As the number of cycles on the actuator increase and wear on the piston seals increases it becomes harder to control the force and speed. The pneumatic actuator will eventually become 'un-controllable' causing increases in reject parts and downtime for repairs.
We reduced air consumption on this machine by an estimated 90%. Currently, we only use compressed air for pick and place of the parts onto and off of the dial.
The target cycle time of 3 seconds was easily achieved. With further refinement we reduced the average cycle time to 2.9 seconds. With approximately 3 million cycles on the system performance has been consistent with no actuator failures and cycle times are still averaging 2.9 seconds.
