For the OP
I have implemented two systems that do this,
One has the product evenly spaced on the conveyor however the phase changes as the machine varies speed (Due to fixed acceleration belts) and the phase change has a transport delay due to the length of the belts. 10 per second using closed loop VSD's.
The other, which may be closer to your system, has the product arriving totally randomly and close together, I have control of three belts where I must accelerate the product to "tray" speed and get the correct phase (position in tray) This is on control logix using servos. (160 units per minute)
Methods - Pretty much as Peter said:
a Gear to lock the axis together, then sensors to detect as the product passes a fixed point, maths to determine what correction move is required, shaped profile correction moves to be as gentle on the product as possible (too rough and the product slips, then your correction move is all out of wack)
For the smartbelts I did use a virtual axis as the infeed master. This axis was then Geared to the "Trays" and I allowed the operators to adjust the phase of this axis for positioning.
I have implemented two systems that do this,
One has the product evenly spaced on the conveyor however the phase changes as the machine varies speed (Due to fixed acceleration belts) and the phase change has a transport delay due to the length of the belts. 10 per second using closed loop VSD's.
The other, which may be closer to your system, has the product arriving totally randomly and close together, I have control of three belts where I must accelerate the product to "tray" speed and get the correct phase (position in tray) This is on control logix using servos. (160 units per minute)
Methods - Pretty much as Peter said:
a Gear to lock the axis together, then sensors to detect as the product passes a fixed point, maths to determine what correction move is required, shaped profile correction moves to be as gentle on the product as possible (too rough and the product slips, then your correction move is all out of wack)
For the smartbelts I did use a virtual axis as the infeed master. This axis was then Geared to the "Trays" and I allowed the operators to adjust the phase of this axis for positioning.