Measuring and testing – Dynamometers – Responsive to force
Patent
1998-09-23
2000-01-11
Noori, Max
Measuring and testing
Dynamometers
Responsive to force
G01L 110
Patent
active
060123419
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND INFORMATION
Known force sensors are designed as frequency-analog resonant mechanical sensors. Such known force sensors include a structure that vibrates in resonance. The oscillation frequency of this structure is variable on the basis of an acting force, such as an acceleration or a pressure, to be detected. Due to the external action of the acting force, the structure vibrating in resonance is deflected so that it changes its oscillation frequency. The structure vibrating in resonance is formed by a spring-mass system, where an increase in sensitivity of a force sensor can be achieved by an increase in the seismic mass, a reduction in rigidity of the springs, or a combination of the two measures.
However, a disadvantage of the known force sensor discussed above is that a reduction in the fundamental frequency at which the structure vibrates in resonance occurs, so that there is a negative effect on sensor dynamics. On the other hand, an increase in sensor dimensions is associated with an increase in seismic mass.
German Published Patent Application No. 4,426,163 describes an acceleration sensor where the structure vibrating in resonance is under a mechanical prestress, so that the force sensor is operated near its mechanical instability. This increases the sensor sensitivity of the force sensor by placing an operating point of the sensor closer to the mechanical instability. The distance of the operating point from the mechanical instability is determined by a parameter of the applied mechanical prestress. However, it is a disadvantage here in that it is difficult to accurately set the distance of the operating point from the mechanical instability, e.g., due to geometric tolerances in the layout of the sensor, due to temperature dependences, and due to layer stresses which occur due to the mechanical prestress and are difficult to control. Especially when the force sensor is to be operated near its mechanical instability to increase sensor sensitivity, even the slightest shifts in operating point will lead to great signal variations and thus signal errors.
SUMMARY OF THE INVENTION
By contrast, the force sensor according to the present invention offers the advantage that it is possible to accurately set a certain selectable distance between the operating point and the point of mechanical instability. Due to the fact that the distance of an operating point of the force sensor of the present invention from its point of mechanical instability is adjustable, it is advantageously possible to compensate for deviations that occur during production or operation of the force sensor of the present invention, e.g., due to layer stresses, temperature dependences and manufacturing tolerances in addition to accurately setting the distance, so that over the operating life of the force sensor of the present invention, it is possible to very accurately and uniformly set and/or readjust the operating point, especially the smallest possible distance from the mechanical instability of the force sensor of the present invention.
In addition, it is advantageous that different measurement ranges can be set on the force sensor of the present invention due to the adjustability of the distance of the operating point from the point of mechanical instability. The distance of the operating point from the point of mechanical instability of the force sensor of the present invention, which is determined by its geometry, can be varied through the operating point adjustment. Different sensor sensitivities are obtained, depending on the distance of the operating point from the point of mechanical instability, and they have different reactions accordingly on an externally acting force to be detected. In addition, it is a great advantage that the operating point of the force sensor of the present invention can be varied within certain limits while being used as intended. This permits switching of the force sensor of the present invention, e.g., from one measurement range to another, in a very advantageous manner, so that a dif
REFERENCES:
patent: 5166892 (1992-11-01), Inoue et al.
patent: 5339698 (1994-08-01), Robinson et al.
patent: 5417120 (1995-05-01), Hulsing, II
patent: 5553506 (1996-09-01), Benz et al.
Funk Karsten
Kulcke Hans-Martin
Laermer Franz
Schilp Andrea
Uhler Werner
Noori Max
Robert & Bosch GmbH
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