Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1991-12-09
1995-04-25
Williams, Hezron E.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
310329, G01P 1509, H01L 41113
Patent
active
054088780
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for measurement of the acceleration of a test body by means of piezo-electric transducers.
BACKGROUND OF THE INVENTION
Devices of this kind are known from EP-A1-0316498 and DE-A1-3038660.
The device according to EP-A1-03136498 comprises a solid cylindrical body which serves as a carrier and at the same time as a mounting base and which has mutually parallel end faces; through which a pin is passed co-axially to the axis of the cylinder and perpendicularly to the end faces so that it projects perpendicularly out of one end face of the carrier. At a distance from the carrier, the pin passes co-axially through a cylindrical seismic mass which similarly comprises end faces perpendicular to the axis of the cylinder. A piezo-electric transducer, which likewise co-axially surrounds the pin, is clamped between the carrier and the seismic mass by means of the pin, which acts as a tightening pin. The pin is slender and resilient and has appreciable play in the transducer. Bending stresses, which in the transducer cause an increase in pressure on one side of the pin and a decrease in pressure on the other, occur under mass inertia forces which load the seismic mass transversely to the axis of the pin. The transducer is provided with divided electrodes which are arranged and connected in correspondence with the pressure stresses arising in push-pull, so that the changes in charge in the electrodes arranged in push-pull are added to provide bending stresses, and the pyro-electric effects caused by heat flow between the carrier and the seismic mass through the transducer compensate for each other.
Devices for the measurement of acceleration should preferably be sensitive to only certain types of acceleration, e.g.: translational or angular, and the axis of acceleration, the acceleration, angular acceleration) and axis of acceleration, the principal axis. However, this is not adequately so in the known device. The known device is a so-called transverse acceleration pick-up, which should respond only to accelerations perpendicular to the axis of the pin. However, because of the need for freedom of tilting of the seismic mass, angular accelerations and linear, accelerations perpendicular to the principal axis have such a strong influence on the measurement that undesired side effects result and in spite of compensation for pyro-electric effects the device is not usable as an accurate accelerometer, but serves virtually only as a sensor.
The known device according to DE-A1 30 38 660 comprises a carrier as well as a seismic mass, which consists of one piece and is so connected with the carrier that it is pivotable relative to the carrier about an elongate bending line. The centre of gravity of the seismic mass and the bending line determine a plane. Arranged at the seismic mass perpendicularly to this plane as well as parallel to the bending line is a piezo-electric platelet which is firmly connected at its ends remote from the plane with the piezo-electric mass and, in the centre therebetween and at the level of the plane, with the carrier. The platelet is polarised in opposite directions parallel to the plane, as well as perpendicularly to its wide sides, which are disposed above and below the central fastening region and parallel to the bending bearing, and is covered by separate electrodes. A third electrode extends on the other side of the platelet and between the fastening regions at the ends. The platelet is compressed on one side of the plane and extended on the other side, thus stressed in shear, by accelerations acting perpendicularly to the plane. The electrodes are so connected together that the piezo-electric effects are added, and these piezoelectric effects are compensated by the pyro-electric effects, which are brought about by heat flow from the fastening point at the carrier through the platelet to the fastening places at the seismic mass.
The transverse compression excitation (k.sub.31), which is present in the afore-mentioned known device, has the disadvantage of a ver
REFERENCES:
patent: 4447755 (1984-05-01), Ghiurea
patent: 5063782 (1991-11-01), Kellett
Brock Michael J.
Pruftechnik Dieter Busch AG
Williams Hezron E.
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