A closed-loop tracking device just developed by Hoerbiger-Origa solves the perennial problem of high speed conveyor belting gradually running off its rolls. High speed band-type conveyor belts run off their rolls when the rolls are not absolutely perfectly aligned, something that is virtually impossible to achieve when the rolls are typically many metres apart in a harsh manufacturing environment. Hoerbiger-Origa has investigated the problem and developed a solution based upon a small diameter 'correction roll', over which the return (non-conveying) run of the belt passes.
This is mounted in an adjustable bracket, so that it can be pivoted about its centre point to form a slightly non-perpendicular angle to the length of the conveyor.
This angling forces the belt to track across the main rolls, either left or right depending on whether it is a positive or negative angle.
An optical sensor tracks the belt's lateral displacement and this information is used to produce a proportional signal for an electronic controller that changes the angle of the roller to compensate for the offset and bring the belt back towards the centre.
The sensor is set to constantly track the position of the edge of the belt, sampling at a regular time base and in effect build up a graph of its displacement.
As the edge of any working belt is likely to be uneven due to wear and tear, software is used to damp out recurring patterns from the graph.
This resides in a single chip controller.
The chip is constantly calculating a new angle for the roll to optimise belt position and feeds this out to the drive mechanism that makes the adjustments.
The mechanism comprises a standard Hoerbiger-Origa rodded pneumatic cylinder mounted close to the roll by a pivot on its end cap.
The rod end is connected to a crank arm that drives a cam to alter the roll angle as the rod is retracted into and extended from the cylinder.
The cylinder and crank arm are sized so as to create a 100:1 ratio turn down for the cam movements, resulting in very fine adjustment of the correction roll's angle.
This accuracy is needed because in a typical band conveyor a 1mm misalignment of the correction roll would cause the belt to run off the drive rolls in under ten seconds.
To overcome the inherent 'sponginess' of pneumatic systems Hoerbiger-Origa fits a brake module to the cylinder.
This grips the rod the instant that the set point is reached and holds it just long enough for the pressures to equalise.
The controller is fitted with an LCD screen and four-button keypad for adjustment of 13 different parameters.
This allows the system to be bought off as a standard unit and tuned for virtually any installation.
Hoerbiger-Origa has also developed a complementary nut and screw mechanism as an alternative for cost-constrained applications.