Position sensing for high process reliability

Position sensing plays an important role in a reliable injection moulding process. Whether for monitoring the end positions of a slide, ejector set or hydraulic cylinder – mechanical and inductive sensors have become essential in modern mould and die making.

Here is an overview of the most common variations for position control of components in the mould.

MECHANICAL LIMIT SWITCHES

Mechanical limit switches are mainly used to check the end position of the ejector set. For operation, they need contact with the part to be monitored. The limit switches can be used regardless of material, surface and geometry. Possible variations are vertical, horizontal, compact or as roller or dome plungers. Limit switches especially designed for high temperature applications or for die-casting can also be used in horizontal or vertical versions.

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INDUCTIVE LIMIT AND PROXIMITY SWITCHES

Inductive sensors produce an electromagnetic field. If an electrically conductive object approaches this alternating field, it will drain energy from it, leading to a reduction of the oscillation amplitude. This change is analysed by the inductive sensor which makes the position monitoring contactless. The inductive limit switches are also used to check the end position of the ejector set. In addition to object detection, they can be used for positioning, counting (cycle), rotational speed of thread formers and general speed measurement. Unlike mechanical switches, the inductive version is dependent on the material, geometry, and surface. Inductive proximity switches are mainly used for sensing objects. High temperature versions for temperatures up to 140°C are also available.

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MAGNETIC PROXIMITY SENSORS

Hydraulic cylinders are often used to operate slides. If the slide is in the wrong position when the mould is closing, it can cause significant damage to the mould. Therefore, it is also important to carry out position monitoring here. Magnetic proximity sensors offer an excellent solution for compact cylinders with aluminium housing. They recognise the position of the ferromagnetic piston rod and transmit the signal. The functioning principle is the opposite of the inductive sensors. The mini magnets inside the magnetic component are aligned, which reduces the vibration losses of the alternating electric field.

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All sensors at Meusburger are PNP normally open contacts. This means that they emit a signal when they detect an object. It is the opposite for NPN normally closed contacts, which interrupt the signal when an object is detected.