Servo System Improves Bottle Line Speed
In implementing a servo-driven control system on a fast moving pill bottle filling line, a large pharma company was able to reduce quality defects, prevent misalignments in pill bottle transfer, and increase overall line speed.
The company needed to improve a system where filled bottles are transferred off a line for vision inspection and capping, then returned to the line. The existing system used a machine with a three-position air cylinder to rotate the bottles off the line to a 90° position for vision inspection, to a second position for capping, and then 180° back to the line.
The customer replaced the pneumatic system with a servo-driven system from Moog Animatics. Animatics SmartMotors with integrated motion control electronics drive the transfer of bottles to the loop for inspection and manage the capping process.
The pneumatics put a severe limit on the line speed as inconsistent air cylinder motion created production and quality issues, says Hack Summer, applications technology manager, Moog Animatics.
Bottles had to be stopped at the vision station to enable the camera to capture a good picture and at the capping station where a pneumatic rotary capper applied and tighten the caps.
Bottles are bar coded upstream with pill count and size information. The high-speed vision system provides redundancy to 200% visual inspection as the camera looks down into the bottle to confirm tab size and color.
“With a pneumatic system you never get consistency on motion. The pressure builds slowly after you open the valve then the air cylinder pressure starts to build more rapidly. The longer it is moving, the faster it goes. They couldn’t guarantee the speed at the vision station to ensure an accurate camera shot,” Summer says.
“A lot of these plants have system air. The compressor may be 100 yards away feeding air to everything on the production floor. If you get a drop in pressure, the arm can’t swing fast enough to keep up with the line. They have no way of controlling that. You can put regulators up stream, but you never know what might happen,” he adds.
Alternately, the air-cylinder driven arms were bouncing at the end of the stop with air pressure fluctuation. “It can slam to a stop so hard you can break open capsules. Or it may take off so fast after grabbing the bottle from the line it swings pills out of the bottle. They had pills landing on the floor,” Summer says.
The unpredictable acceleration and deceleration of the pneumatic driven arms created flow control issues. Abrupt stops of the cylinder caused bottles to be misaligned with the grippers; bottles hit the end of the gripper instead of going into the fork causing the line to clog up with bottles.
The servo system provides controlled motion profiles enabling soft starts and stops. “It is crucial to have a controlled slow motion and stops. And you have to
rapidly speed up to keep things moving,” Summer says.
The Smart Motors are hooked to a 50:1 gear head with arms for handling the transfer to the vision station and capping. One SmartMotor swings the bottle out in the 180° loop where a consistent speed is maintained at the vision station. A second motor replaces a pneumatic rotary motor for capping. Capping occurs without a stop as the arm swings to follow the bottle.
The motor detects cap presence and placement signaling to the PLC that the cap is tightened properly. Encoders provide a unique digital code for each position of the shaft. The motor on the motor shaft looks for a certain number of encoder counts to detect if for example the cap is jammed after only five turns or strips out after ten turns.
“We use 4000 encoder counts for a single shaft turn, or 4000 counts per revolution. So in this application you expect it to come to a stop after around 40,000 counts, plus or minus 100 counts or so,” Summer says.
The SmartMotor solution addresses development time and costs. The motors can be programmed to act on the same commands used with the pneumatic rotary cylinder system they are replacing. So the PLC code controlling the line required no reprogramming.
Manufacturers are finding today they have to send the same quality out, but they have to run faster.
“This customer could not run the pneumatic arm any faster without messing things up. We were able to go faster, get consistent speed under the camera, track and cap while we are moving, and guarantee a nice soft stop at the end of the movement. The net result—they could run more pill bottles,” Summer says.
Published in Pharmaceutical & Medical Packaging News, September 2012, Volume 20, No. 8.