Geometrical instruments – Miscellaneous – Light direction
Patent
1997-07-25
1999-08-03
Bennett, G. Bradley
Geometrical instruments
Miscellaneous
Light direction
G01B 700
Patent
active
059309059
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and a device for measuring the angle of a rotatable body, in particular of a body rotatable by 360.degree..
In connection with various applications, in particular with arrangements with the aid of which the angular position of a rotatable shaft is to be determined, there is a desire to know the exact position of the shaft immediately following start-up of the arrangement. This requirement can be best met with the aid of analog angle sensors, for example potentiometers, which provide the valid angular position in the form of a voltage in every position following start-up.
When such arrangements for angular measuring are employed for angular ranges which are greater than 360.degree., the problem arises that it can no longer be determined in which revolution the shaft is. However, incremental sensors can be used for evaluating angular ranges which are greater than 360.degree., in which the angular position is determined by forward or backward counting of pulses. However, it is not possible to perform an absolute angle measurement with such incremental sensors, because it is only possible to count increments which move past a counter.
So that an angular measurement of angular ranges larger than 360.degree. is possible, it is proposed in not yet published German patent application DE-P 44 09 892 in connection with the detection of a steering angle of a motor vehicle, to perform the determination of the steering wheel angle, which extends over a range of .+-.720.degree., with the aid of a planetary gear system. In this case the number of teeth of the planetary gear system is dimensioned in such a way that a value of exactly 4 results for the gear ratio between the steering axle and the pick-up disk to be scanned. The pick-up disk to be scanned therefore only rotates once while the steering angle is changed by .+-.720.degree.. By means of applying a code to the pick-up disk and scanning it with a suitable sensor it is possible to determine the position of the pick-up disk immediately following start-up, and a steering wheel angle determination is also immediately possible with this.
This known arrangement for the angular measurement of angular ranges greater than 360.degree. has the disadvantage that an exactly dimensioned planetary gear system is necessary and that in addition an elaborate absolute sensor system is required.
SUMMARY OF THE INVENTION
In contrast thereto, the method in accordance with the invention and the device in accordance with the invention for angle measurement in connection with a rotatable body, in particular a body rotatable over more than 360.degree., has the advantage that a quite general absolute angle measurement is possible even over several revolutions without an elaborate planetary gear being required. Measurement errors are reduced by the use of two sensors, which detect two different angles. The measuring principle can be used in connection with all types of angle sensors, such as optical, magnetic, capacitive, inductive, resistive sensors, i.e. arbitrarily with contact and contact-free sensors.
These advantages are achieved in that the shaft, whose angular position is to be determined, is provided with a gear wheel or a gear rim which cooperates with two further gear wheels, whose angular position is continuously detected with the aid of a sensor each, and in that the angle to be determined is calculated in a suitable manner from the two measured angles.
It is particularly advantageous that the angular range and the angular exactness can be freely set by the appropriate selection of the number of the angular markers or teeth of the individual gear teeth or gear rims. The arrangement of the gear wheels can be selected to be such that desired advantages are created. In this case the gear wheels can be arranged in a single plane or in different planes.
Further advantages of the invention are achieved by means of the steps recited in the dependent claims. It is particularly advantageous in this connection that too lar
REFERENCES:
patent: 2623936 (1952-12-01), Kennedy et al.
patent: 3077671 (1963-02-01), Lindholm et al.
patent: 4072893 (1978-02-01), Huwyler
patent: 4660288 (1987-04-01), Dangschat
Abendroth Manfred
Braun Hans
Jost Franz
Marx Klaus
Zabler Erich
Bennett G. Bradley
Robert & Bosch GmbH
Striker Michael J.
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