The company Maschinen-Förder-Produkte (MFP), a manufacturer of conveyor belt and system technology for a wide range of industries and applications, was commissioned by a customer to modernize an existing conveyor concept for a plastic injection moulding plant. In this plant, the pallet runners produced pass through an MFP floor conveyor for cooling, which holds more than 30 runners at a time. As hot plastic injection molded parts tend to deform, they must be kept precisely in shape during the cooling process to ensure the desired final quality. This task is performed by precisely positioned pressure beams. The customer now wanted a fully automatic adjustment of the pressure bars in order to minimize set-up times and at the same time achieve 100% repeatability.

A floor conveyor from MFP for cooling hot plastic injection molded parts.

© MFP

In the modernized system, automated linear axes take over the positioning of the pressure beams. They consist of double-tube axes from RK Rose+Krieger and specially adapted electromotive actuators from Lenord + Bauer. A total of 18 automated infeed axes are used to position the pressure beams - six on each of the three levels of the multi-level conveyor.

As the axes have to compensate for comparatively high bending moments, MFP chose 'EPX30' double-tube units. The robust, self-locking tube system linear units have a sliding guide and a trapezoidal threaded spindle. In this application, this spindle is supported by a ball bearing. For use in environments with fine dusts, it can optionally be fitted with a plain bearing. It is equipped with a driven and a moving second guide carriage, both of which are connected to a clamping plate. The larger support distance between the carriages ensures that the axis can absorb high (bending) moments. Sliding bushes in the guide carriages reduce the drive torque on the guide tubes and minimize wear on the carriage. The double tube unit is suitable for manual and motorized adjustment as well as for installation in any position at ambient temperatures from 0 to +60 °C and has a pitch accuracy of ±0.2 mm/300 mm stroke.

Actuators for automatic positioning

Each axis is automated with a 'Powerdrive' actuator from Lenord + Bauer. Due to the cramped installation situation, drives with a stepped housing were specially designed for such applications. With an installation depth of 96 mm, they offer a nominal torque of 5 Nm. Each actuator is a complete mechatronic unit consisting of a brushless DC motor, 32-bit microprocessor, output stage and gearbox.
An adapter kit developed by Lenord + Bauer for the 'EPX30' ensures that the drive sits securely directly on the spindle end of the linear axis. In addition to the friction-locked shaft connection, this also contains a torque support that absorbs the forces that occur and forms the necessary floating bearing.

The decentralized 'Powerdrive-Box' control unit from Lenord + Bauer is used to connect the actuators to the system. It controls up to five drives, supplies them with power and enables communication. A pluggable interface makes it easier to integrate the box into standard industrial networks and ensures data exchange with the system control. In the MFP machine, the positioning system is linked to a Siemens S7-314 via Profinet. Ready-made software modules integrate the positioning system into the control system, in which the various skid types are stored in a recipe management system. Once the recipe has been selected, the actuators automatically move to the corresponding position.

Author:
Bernd Klöpper is Marketing Manager at RK Rose+Krieger in Minden.