A new method for direct measurement on the loaded parts of the machine

For the direct measurement of the deformations of loaded parts such
as beams, supports and masts which are fitted, for example, on presses, injection moulding or stamping machines or on levers, gearbox casings and brake callipers, tecsis offers a new process in which pressed-in sensors are used.

This method uses a type of sensor with a cylindrical external contour.
The sensor is pressed into a reamed hole to measure the extension of the component to be monitored. The hole into which the sensor has to be pressed has a smaller diameter than the cylindrical diameter of the sensor.

Simple fitting and replacement of thepressed-in sensor

The pressed-in sensor is fitted using
a commercially available press. To achieve this a hole must be drilled at a predetermined place in the component in which the sensor is to be fitted. An adaptor sleeve is pressed in and the sensor is pushed into the adapter sleeve. The use of an adapter sleeve enables the sensor to be easily changed. The assembly forces are about 10kN which is in a practical range.

Thus the parts in which the pressed-in sensor is fitted can be further machined in the normal flowline. The last process consists of setting the zero and end points (sensitivity) of the amplifier (which is also be integrated in the sensor) with the help of a handprogramming device. To set it up a defined load is put on the machine in which the sensitised component is installed. If it is desired that the sensor should shut down the machine (for example for overload protection) the endpoint can be determined by running up the machine to the maximum load.

The application of pressed-in sensors using a gearbox housing as an example

Measurement of the driving torque of a shaft ina gear box housing: In the gearbox housing there are normally roller bearings to support the shafts. In many gearbox designs these roller bearings must carry single sided radially applied loads proportional to the torque. Thus it is possible to record load proportional extensions in the gearbox casing.The pressed-in sensor which is fitted at a suitable place in the cover gives an electrical signal proportional to the torque.

Long duration investigations have shown that the signal is very stable even under adverse conditions: In tests of over 100 000 full load cycles the change was less than 1% both for the zero point and the end point.

There are hardly any limits to the application of pressed-in sensors provided that the strength of the component to be measured is sufficient. The yield strength should however exceed 200 MPa. Components made of steel and aluminium pressure die castings present no problemfor this application. High strength materials are also very suitable for the application of pressed-in sensors.

_{Fig. 1: Measuring method using sensor pressed into the hole in the component}

The advantages of the measuring
method using pressed-in sensors lie
firstly in the small space taken up by the sensors themselves and secondly in the very low temperature sensitivity of the measurement signal which is due to the measurement principle.

_{Fig. 2: Measuring procedure with pressed-in sensor and adaptor bush}


If the pressed-in sensor is put into a series manufactured machine it depends on the complete support system in all project stages. For such a project the following preparation steps are necessary in the procedure planning:

_{Fig. 3: Application examples platform technology}


tecsis offers the complete measuring chain with a large choice of programmable amplifiers some of which can be fitted in the sensor. 0…10 V and 4...20 mA are available as standard output signals. Already two sizes of the new type of sensor are in series production. The external diameter of the sensors is 12 mm and 20 mm. The load measurement on machine components by means of pressed-in sensors is a forward looking alternative to the known procedures and is a convincing solution due to its cost-benefit ratio.

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