Angle measuring instrument for a rotating shaft

Details Angle measuring instrument for a rotating shaft Angle measuring instrument for a rotating shaft

2002-11-15

2004-12-07

Patidar, Jay (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207170, C324S173000, C033S0010PT, C341S015000

Reexamination Certificate

active

06828783

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to Application No. 101 58 223.4, filed on Nov. 16, 2001 in the Federal Republic of Germany, which is expressly incorporated herein in its entirety by reference thereto.
FIELD OF THE INVENTION
The present invention is directed to an angle measuring instrument.
BACKGROUND INFORMATION
Angle measuring instruments are used to measure both the angle of rotation of a rotating shaft within one rotation, as well as the number of rotations executed by the rotating shaft, so that, by combining the two measuring results, the absolute position of the rotating shaft can be determined even after several rotations have occurred.
For example, a single-turn rotary position transducer is used to measure the angle of rotation of a rotating shaft within one rotation. When configured as a rotary encoder, the transducer allows both an angular measurement to be taken in incremental measuring steps at the rotating shaft, as well as an absolute angle determination to be made within one single shaft rotation.
To determine the number of shaft rotations that have occurred, multiturn rotary encoders are used to determine the absolute angular position within one shaft rotation, i.e., between 0° and 360°, via an encoder disk (a disk containing a coded pattern) which is connected to the shaft and which is scanned with the aid of a suitable photoelectric scanning unit. To obtain the required information regarding the number of effected shaft rotations, typically a reduction or step-down gear is provided, by way of which, with a rotating shaft, the one or more partial disks or encoder disks is/are set into a rotary motion at a low number of revolutions per unit of time, i.e., a slow speed. The rotational movements of the additional encoder disks are likewise measured using one or more photoelectric scanning units, so that, on the basis of the known reduction of the rotary motion of the additional encoders disks, the number of executed shaft rotations can be determined. It is also possible to measure the absolute position of the rotating shaft over a plurality of rotations.
From German Published Patent Application No. 28 17 172, partial disks coupled to gear wheels may be photoelectrically scanned. In this multi-stage incremental shaft encoder, a first encoder disk is provided concentrically to the shaft, and the other succeeding encoder disks are configured in a common plane. The encoder disks are scanned photoelectrically such that the receivers are located on the side of a board facing the encoder disks, and the receivers on another board fixed to the housing.
Since the process of photoelectrically scanning a plurality of partial disks using one photoelectric scanning device, as the case may be, is expensive and susceptible to contamination, such that it can only be carried out under appropriate ambient conditions or by properly encapsulating the measuring device, to reduce the outlay for components, German Published Patent Application No. 196 26 654 describes measuring the rotary motion of gear wheels using strain-sensing elements, which are in a positive contact with the particular gear wheel. In contrast to the spatial configuration of the reduction gear or of the individual gear wheels in a common plane, as described German Published Patent Application No. 28 17 172, in the system illustrated in German Published Patent Application No. 196 26 654, the individual gear wheels are staggered in the axial direction.
It is therefore an object of the present invention to provide an angle measuring instrument of the type set forth at the outset, which will enable the number of executed shaft rotations to be simply determined, which is insensitive to contamination, is suited for simple and high-resolution scanning operations, and which allows a plurality of specific configuration embodiments having different space requirements.
SUMMARY
The above and other beneficial objects of the present invention are achieved by providing a measuring instrument as described herein.
An angle measuring instrument according to the present invention includes a simple configuration and a functioning that is insensitive to contamination, which renders possible a plurality of exemplary embodiments having different space requirements, and which is equally suited for a simple as well as for a high-resolution acquisition of the number of executed shaft rotations.
German Published Patent Application No. 197 51 853 describes the principle of inductive scanning for a device for determining the absolute angular position of a rotating shaft within one shaft rotation, i.e., for a pure single-turn rotary position transducer. However, no reference to applying this principle to a multiturn rotary position transducer can be inferred from this publication.
The present invention achieves the objective by starting out from a fundamental consideration that, given a suitable designed multiturn rotary position transducer, the principle of inductive or capacitive scanning may be applied, while attaining the associated advantage of insensitivity to contamination and a rugged, economical type of construction, even in the case of a multiturn rotary position transducer. In particular, a multiturn rotary position transducer which functions in accordance with the inductive or capacitive scanning principle to determine both the absolute angular position of a rotating shaft within one shaft rotation, as well as to determine the number of executed shaft rotations, may be combined with a single-turn rotary position transducer which functions in accordance with the principle of inductive or capacitive scanning.
In the various exemplary embodiments of the approach according in the present invention, the multiturn rotary position transducer, which functions in accordance with the inductive or capacitive scanning principle, may also be combined with any other single-turn rotary position transducers, which work, for example, according to the photoelectric or magneto-resistive scanning principle, without affecting the advantage of a simple design and of insensitivity to contamination of the multiturn rotary position transducer which works in accordance with the inductive or capacitive scanning principle.
The sensor device of the multiturn rotary position transducer, which works according to the inductive or capacitive scanning principle, may include at least one sensor track having at least two sensor windings, which are phase-shifted with respect to one another and which emit phase-offset, periodically modulated sensor signals in response to the relative motion between the scanning device and the graduation structure, while the device for generating an electromagnetic excitation field has exciter elements positioned on both sides of the sensor track which produce the most homogeneous possible electromagnetic field in the region of the sensor track.
The exciter elements may include a current-carrying conductive track or of a plurality of current-carrying conductive tracks disposed in parallel to one another, the conductive tracks of the exciter elements being interconnected such that the current flow is oriented in opposite directions in the conductive tracks positioned on both sides of the sensor track. In this context, the graduation structure may be placed on a circular graduation board and include a first, circularly formed graduation track, made up of an electrically conductive circular segment and an electrically non-conductive circular segment. The scanning device may include a scanning structure which is positioned on a circular scanning board and may have a sensor device which has the sensor track assigned to the graduation track, the sensor windings of the sensor track allowing an absolute positional determination over the detectable measuring range.
At least one graduation and one inductive scanning, including a sine and cosine graduation track, may be assigned to each gear unit, so that the angular information relevant to the gear unit in question may be acquired for each gear uni

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