Pete Kepf, Certified Vision Professional -
Bottling lines operate at incredible speeds. This speed combined with
the machine’s complexity increases the potential for catastrophic damage
should an error occur. A miss-fill or cap mis-alignment can occur in the
blink of an eye, making the use of automated inspection at strategic
locations within the machine mandatory. One such location is the capper.
The capper, as its name implies, is where the cap is inserted onto the
bottle top. The bottle passes beneath the capper traveler which moves
with the bottle and spins at the same time to tighten the cap. A torque
sensor senses when the cap is tightened to specification and the capper
moves away from the bottle.
Although the caps may be torqued to within specification, flash or some
other obstruction could cause a poor seal. A reliable way to verify that
a cap is seated properly is to measure the distance between the shoulder
of the bottle and the lower edge of the cap. Only one camera and a back
light are required to perform the inspection.
The control challenge was to store the inspection results (pass/ fail)
of the camera for triggering of a downstream reject mechanism.
Technical issues: machine access for sensor and camera; unequal part
The picture above shows a simplified layout. The actual installation
consisted of a sensor and a camera. The encoder and reject mechanism
were part of the existing machine
A sensor detects the part at the beginning of the process. A sensor
pulse and an encoder pulse are sent to the controller; the controller
stores the relative position of the “current” part. The distance in
encoder pulses between the sensor and the camera in pulses is known.
When that part reaches camera location the controller sends a pulse to
that camera and light. The inspection is performed and the results are
stored. The distance between the camera and the reject mechanism in
pulses is known. If the value of the inspection is “fail”, then the
controller sends a pulse to the reject mechanism. The controller/ timer
provided a simple method to sequence control without a PLC.