In Figure 1. is shown a simplified diagram of the measuring set-up.

          In Figure 2. is shown a photograph of the measuring set up.

Figure 1

  1. Lever rotating at ball bearings 7.
  2. Fall-stop.
  3. Release mechanism.
  4. Weight.
  5. Support.
  6. Base-plate.
  7. Ball bearings.
  8. Break-contact.
  9. Make-contact.

On the base 6 is mounted a support 5. By means of two ball bearings 7 an aluminium lever 1 is rotating attached to support 5. About halfway the lever 1 is attached a weight 4 of about 0.4 kg. The length of the lever 1 is about 50 cm and its weight is about 0.1 kg. The lever 1 is hold in its start position by the release mechanism 3.

On lever 1 two contacts are mounted: a break-contact 8 with connectors A and B and a make contact 9 with connectors C and D. The release mechanism 3 is constructed by a pin which can be pulled away from the lever 1 by activating a solenoid by an electric impulse. At the start of the measurement, the end of lever 1 must rest on the end of the to be measuring key.

The connectors A and B of break contact 8 and the connector C and D of make contact 9 are via an electronic circuit connected to an electronic time measurement device, capable of measuring time slots of 5000 100000 microseconds. When the release mechanism is activated the following happens:

  1. The gravity force pulls down lever 1 plus the end of the key and at the same moment:
  2. Opens the contact 8 and A and B are disconnected and starts the time measurement.
  3. When the end of the key is about 5 mm. downwards, contact 9 closes and stops the time measurement.

Knowing the fall time and the distance the key travelled during the fall time, the force Fd required, to press the key down in a certain time td can be calculated with the following formula:

In this formula is:

A software program has been designed which, after entering the static down-weight and the measured fall time, calculates for a number of press down times the required dynamical forces. (See table 1 and 2)

Figure 2.

           Measuring results.

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