HBM's piezoelectric force washers enhance press-fitting of bearings, bushings and bolts

Servo-electrically driven press-fir units are increasingly used for press-fitting of bearings, bushings and bolts. Encoders and force washers are often used for recording process parameters.

The encoder provides the servo motor with direct proportional displacement information, with the piezoelectric force washer often being installed inside the press plunger. Sensors integrated in the machine design enable a wide range of press operating modes to be implemented: In addition to the conventional end position or maximum force control, force-controlled feed or force-controlled positioning can now be implemented as well, because the instantaneous force value is available in the press control. This is possible thanks to the fact that CFW force washers from HBM can be easily integrated. Direct force measurement offers excellent measurement characteristics and, compared to measurement in the motor current, provides substantial benefits in terms of accuracy and reliability.

Servo-electrically driven press-fit station equipped with piezoelectric force washers from HBM

This application enables the new CFW piezoelectric force washers to be very easily integrated into the mechanical system and offers huge benefits to design engineers and users.

• Compact design
• High overload capability/long service life
• Excellent linearity and reproducibility
• Enables an extremely wide measuring range to be covered using a single sensor type.

The split diaphragm (see figure) ensures perfect force application, even if the sensor is not loaded centrically. This is particularly important with uneven force application in compact mechanical systems like press plungers. No additional force application parts are required and substantially more compact designs can be implemented. Another advantage of this design is its high torsional stiffness. The sensor can be perfectly centered through its internal or external diameter without producing any hysteresis errors. The sensor's ruggedness is completed by the integrated plug protection which is to prevent mechanical damage to the electrical connection.

Because of its extremely high stiffness, the sensor has virtually no nominal displacement. This helps to prevent any falsification of the resolver signal from the motor related to the real press position. Since its sensitivity of 4.3 pC/N is independent of the measuring range, a single sensor type enables the whole bandwidth of a press family with different nominal (rated) forces to be equipped.

Innovative ideas and consistent development enable HBM to offer force sensors opening up completely new opportunities in industrial force measurement and providing outstanding measurement properties. CFW force washers are initially available in two sizes, with nominal forces of 50 kN and 140 kN and cover all common assembly and testing applications. Special versions are available on request.