Why does a suction pad adhere to a workpiece?

In spite of its name, a suction pad (or vacuum gripper) is held against a workpiece by the surrounding pressure – the atmospheric pressure – as long as this is higher than the pressure which exists between the suction pad and the workpiece.

This pressure difference is achieved by connecting the suction pad to a vacuum generator, which draws air out of the suction pad. When the suction pad touches the workpiece, it forms a seal between the atmosphere and the space under the suction pad.

The holding force is directly proportional to the difference between the atmospheric pressure and the pressure in the space bellow the suction pad.

How does an ejector work?

Ejectors operate on the so-called Venturi principle. Compressed air flows into the ejector at A. The narrow cross-section of the drive gas nozzle B accelerates the air to a supersonic speed. When it leaves this nozzle, the air expands and flows through the second nozzle into the silencer C.

This results in a low pressure in the chamber around the drive nozzle B and air is drawn in through input D. This air is ejected, together with the drive air, through the silencer C.

In addition to basic ejectors, there is another group of ejectors called the compact ejectors. These operate on the same principle as the basic ejectors, but have further components for special functions.

Compact ejectors are equipped with suction and blow-off valves for picking up and blowing off the parts being handled, a vacuum switch for monitoring and regulating the vacuum level and a filter on the vacuum side.

The valves and the vacuum switch also permit implementation of an air-saving function which ensures that compressed air is consumed only when the vacuum drops below a limit value set in the vacuum switch.

The advantage of compact ejectors is that all necessary additional components are integrated, reducing the time and costs for installation. A compact ejector also costs less than the individual components would cost if purchased separately.

How does a vacuum blower work?

In a blower, air is drawn into the housing by the rotating blades and is accelerated and compressed there. In other words, kinetic energy is transferred from the impeller to the air. The movement of the air by the impeller blades generates a vacuum on the suction side (B). The compressed air leaves the blower through the outlet opening (C).

Due to their high flow rate, vacuum blowers are capable of evacuating large volumes in a short time. On the other hand, however, the vacuum level they generate is relatively low.

How does a vacuum pump work?

A vacuum pump has an eccentrically mounted impeller with vanes which are pushed outwards by the centrifugal force when the impeller rotates and form a seal between the impeller and the cylinder wall. Due to the eccentric mounting of the impeller, the volume of each “cell” between two vanes varies cyclically. On one side of the pump, their size increases, allowing the air to expand and generating a vacuum. On the other side, they become smaller and compress the air.

Vacuum pumps can generate high vacuum levels, but their suction capacity is relatively low.

How does a vacuum switch work?

Various designs of vacuum switches exist: mechanical, pneumatic and electronic. In the mechanical and pneumatic versions, a diaphragm reacts to variations in the vacuum level and actuates a mechanical switch or a valve. In the electronic version, the vacuum is measured by a piezo-resistive sensor which converts the level into an electrical signal.

It is also possible to generate an analogue electrical signal which rises proportionally as the vacuum increases.

Vacuum switches can be used to monitor and control processes.

All types of vacuum switches permit adjustment of the value at which they are actuated. On some models, the switching hysteresis can also be adjusted.