milldrone
Member
I'm having some difficulty with some equipment that has two ACS600 drives. Sorry if this is a little wordy. The drives may not be the problem, but the symptoms lead one to think that they might be part of the problem.
The drives (2) are in DTC mode and they power two conveyors, one feeding to another with a gap in between. The gap is about 28" and there are four cameras (top, bottom and each side) viewing the product (lumber) in the gap as it passes from one conveyor to the other. There is only one encoder it is currently driven by a synchronous timing belt from the drive shaft of one conveyor. There are no gear boxes. Each conveyor has identical timing belt drives with a jackshaft for reduction. The conveyor belt itself is a synchronous timing belt with a special high friction surface that contacts the lumber. This conveyor belt runs on timing belt pulleys for head and tail drums. The timing belts are in good condition (no missing teeth). The timing pulleys are in good condition (no missing teeth). All shaft connections look good. It appears there is no slippage between the motor shafts and the conveyor belts as it is 100% timing belt drive. There are elastomeric tensioned hold down wheels to pinch the lumber between the wheels and the conveyor belt.
The motors are identical (Baldor super E gold 3 hp@ 1750). Typical production speed is 1250 rpm at the motor. The ACS600's get their speed reference from a 0-10v analog signal from a AD DL240. The drives share the same analog voltage reference. In production the speed reference never changes while lumber is present (except for catastrophe). Any lumber that is scanned when the speed is changing is set aside and rerun. The motors have been tuned to the ACS600 drives by disconnecting the belts and letting the the drives do their “magic” for tuning DTC. Percent of torque readings from the drives digital displays are 13% and 18% respectively. Hand held tachometer/ speedometer readings are steady on one conveyor at 398 ft per min. the other conveyor reads 398 for 98% of the time then gives a 397.5 flicker. The readings are while the the conveyors are running but no lumber is present. While lumber is running the digital displays of “P speed” change by one digit ie. 398 to 397.
Now for the problem. Length measurements are inconsistent from the encoder with reality. If we scan the same board twice we get the same reading both times. If we find boards of exact length (+- .030”) we get results that are 1.25” to 2” different.
What I have done is installed a second encoder ( with a DL06) to test against the original. Then I was able to run both encoders at the same time. The results were the same (whithin tollerance) as far as the original encoder reading vs my temporary encoder ie. 242.8” vs 242.7” and the board measured 240.2. The next board was the same actual length 240.2” and the encoder readings original= 240.4” temp= 240.3”. By the way the second encoder is totally separate and so is the measuring photo eye. This testing has confirmed (to me) that the boards are slipping on the conveyor surface. In another test I measured the boards with a measuring wheel on my test encoder there by bypassing the conveyor to board slippage issue. When measuring the lumber directly with the wheel the measurements agree test encoder to reality.
Now for the second part of my problem. The vision system needs to be recording encoder pulses while the lumber is in the gap with out anything obstructing their view. This is why the Oem tied the encoder to the conveyor driveshaft with a timing belt. The Oem controller will not accept two encoders at once. I'm confident I will never be able to eliminate the mechanical slippage between the conveyor belts and the lumber.The mechanical arrangement does not lend itself to one drive. If more details are required I will be glad to respond, this post is already a little long. Has anyone switched between two encoders to one controller?
The drives (2) are in DTC mode and they power two conveyors, one feeding to another with a gap in between. The gap is about 28" and there are four cameras (top, bottom and each side) viewing the product (lumber) in the gap as it passes from one conveyor to the other. There is only one encoder it is currently driven by a synchronous timing belt from the drive shaft of one conveyor. There are no gear boxes. Each conveyor has identical timing belt drives with a jackshaft for reduction. The conveyor belt itself is a synchronous timing belt with a special high friction surface that contacts the lumber. This conveyor belt runs on timing belt pulleys for head and tail drums. The timing belts are in good condition (no missing teeth). The timing pulleys are in good condition (no missing teeth). All shaft connections look good. It appears there is no slippage between the motor shafts and the conveyor belts as it is 100% timing belt drive. There are elastomeric tensioned hold down wheels to pinch the lumber between the wheels and the conveyor belt.
The motors are identical (Baldor super E gold 3 hp@ 1750). Typical production speed is 1250 rpm at the motor. The ACS600's get their speed reference from a 0-10v analog signal from a AD DL240. The drives share the same analog voltage reference. In production the speed reference never changes while lumber is present (except for catastrophe). Any lumber that is scanned when the speed is changing is set aside and rerun. The motors have been tuned to the ACS600 drives by disconnecting the belts and letting the the drives do their “magic” for tuning DTC. Percent of torque readings from the drives digital displays are 13% and 18% respectively. Hand held tachometer/ speedometer readings are steady on one conveyor at 398 ft per min. the other conveyor reads 398 for 98% of the time then gives a 397.5 flicker. The readings are while the the conveyors are running but no lumber is present. While lumber is running the digital displays of “P speed” change by one digit ie. 398 to 397.
Now for the problem. Length measurements are inconsistent from the encoder with reality. If we scan the same board twice we get the same reading both times. If we find boards of exact length (+- .030”) we get results that are 1.25” to 2” different.
What I have done is installed a second encoder ( with a DL06) to test against the original. Then I was able to run both encoders at the same time. The results were the same (whithin tollerance) as far as the original encoder reading vs my temporary encoder ie. 242.8” vs 242.7” and the board measured 240.2. The next board was the same actual length 240.2” and the encoder readings original= 240.4” temp= 240.3”. By the way the second encoder is totally separate and so is the measuring photo eye. This testing has confirmed (to me) that the boards are slipping on the conveyor surface. In another test I measured the boards with a measuring wheel on my test encoder there by bypassing the conveyor to board slippage issue. When measuring the lumber directly with the wheel the measurements agree test encoder to reality.
Now for the second part of my problem. The vision system needs to be recording encoder pulses while the lumber is in the gap with out anything obstructing their view. This is why the Oem tied the encoder to the conveyor driveshaft with a timing belt. The Oem controller will not accept two encoders at once. I'm confident I will never be able to eliminate the mechanical slippage between the conveyor belts and the lumber.The mechanical arrangement does not lend itself to one drive. If more details are required I will be glad to respond, this post is already a little long. Has anyone switched between two encoders to one controller?