Geometrical instruments – Distance measuring – Scale reading position sensor
Reexamination Certificate
2003-03-10
2004-11-09
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Distance measuring
Scale reading position sensor
Reexamination Certificate
active
06813844
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to German Application 10210326.7 filed 08 Mar. 2002.
FIELD OF THE INVENTION
The invention concerns a magnetic measuring structure with portions which are magnetised alternately in the longitudinal direction, referred to herein for the sake of brevity as a ‘measuring scale’, for a length measuring apparatus, and a process for the production thereof.
BACKGROUND OF THE INVENTION
When arranged on the periphery of a cylinder such a length measuring apparatus can naturally also be used basically for angle measurement purposes.
The length measuring apparatus includes on the one hand a measuring scale on which the units of length are recorded and a sensor unit which is moved relative to the measuring scale in the measuring direction. Generally in that case the arrangement registers the number of units of length which are covered on the part of the sensor unit in that relative movement, that is to say how many units of length the sensor unit entirely or partially travels over. The absolute position at the end of the relative movement can only be calculated if the starting position, prior to the relative movement, is known.
For that purpose the straight or curved measuring scale has respective codings, generally uniform and periodic codings, which are arranged in succession in the measuring direction, only in one single track or in a plurality of tracks in mutually juxtaposed relationship, with the pitch spacing being different from one track to another. In addition, provided along the measuring distance, in general mostly only at a single lengthwise position, there is a reference mark, the position of which represents the absolute zero position and over which therefore the sensor unit first has to travel once, for setting the apparatus in operation, in order thereby to predetermine an absolute start value.
In addition however length measuring apparatuses which provide for absolute measurement are also known. In that case, by virtue of the design configuration of the measuring scale divisions and the evaluation procedure involved for example by just once setting the sensor to any location on the measuring scale it is possible directly to ascertain the absolute position of the sensor on the measuring scale without relative displacement of the sensor with respect to the measuring scale and without the need to initially move the sensor to a reference point on the measuring scale.
Irrespective of whether the system involves an incremental or an absolute length measuring system, the measuring apparatus according to the invention includes one or more or a multiplicity of magnets which implement modulation of the signal to be detected. For example the individual units of length are applied in sequence in the measuring direction to the measuring scale, in the form of different magnets or magnetisations, by way of example in the form of segments which are each of equal length in the measuring direction and which involve alternate poles.
The sensor unit which is moved relative thereto in the measuring direction and which, besides the actual sensor, generally already includes at least parts of the electronic evaluation system, detects the magnetic field which constantly alters in the measuring direction, as an analog signal in the form of a sinusoidal oscillation or a sine-like but uniform oscillation. A substantial advantage of this method is the fact that the sensor can be moved at a spacing relative to the measuring scale, that is to say in a contactless mode. The measuring scale and also the sensor are thus not subjected to any mechanical wear. In addition there is only a limited need for parallelism of the direction in which the sensor is guided relative to the direction in which the measuring scale extends.
In particular the spacing between the sensor and the measuring scale which should be at about 1.0 mm may also change somewhat.
The measuring scale may have one or a plurality of mutually juxtaposed tracks which each have the magnetised segments of alternate poles.
Thus, the one track, as a pure counting track, can be equipped with regular sequences of magnetisation portions while the other track serves to mount reference marks—in punctiform or region-wise manner—, that is to say reference marks for the purposes of marking for example the absolute zero point, the end of the measuring scale or the like. Such a reference track may be non-magnetised or additionally regularly magnetised in the lengthwise region between the reference marks.
Likewise, absolute encoding of the measuring structure can be effected by means of a plurality of mutually juxtaposed tracks, in which case then the length of the differently poled magnetised segments on the individual tracks is mostly of different magnitude.
Hereinafter—without however limiting the invention thereto—consideration will be based on the specific case where both the regular sequences of magnetisations for registering a distance covered and also at least one irregular sequence of magnetisations for producing reference marks are present on one and the same track. For that purpose, the width of the track can also be divided into two narrow sub-tracks, in the region of the irregular sequences.
In that respect, the problem which arises is that of magnetising the measuring scale alternately, regularly and irregularly, with the lowest possible level of unwanted stray flux during the magnetisation operation so that, in the later operation of detecting the alternate magnetic segments of the measuring scale, the result achieved is a sinusoidal electrical signal which is as precise as possible, and which has as few harmonics as possible.
In this connection, it should be explained (see
FIG. 1
b
) that a sensor which moves at a given spacing above the surface of the measuring structure which has the magnetised segments of differing poles, in the longitudinal direction thereof, detects the gradient, that is to say the first derivative, of the magnetic field lines which extend in a U-shape from each pole to the respectively adjacent poles, and in so doing pass with their free ends into and out of the surface of the measuring structure. Accordingly, the result produced is an electrical signal which is sinusoidal with a zero passage or a reversal in the curvature of the sinusoidal curve at each of the limits between two differently polarised magnetic segments.
For that reason, in regard to the regular sequence of segments, and the irregular segment sequence disposed therein, which are to be used as reference marks, care is to be taken to ensure that those irregular segments are not so long that they achieve double the length of the regularly arranged segments, but are at a maximum only 1.5 times, in particular only 1.3 times, that length (see
FIG. 1
b
).
SUMMARY OF THE INVENTION
Based on that situation, the object of the present invention is to provide a process and an apparatus for producing a magnetic measuring scale which satisfies the specified properties in respect of the electrical measuring scale, in spite of the apparatus being of a simple and inexpensive structure and the process being simple and inexpensive to implement.
Due to the L-, C-, U-, F- or 8-shaped configuration of the magnetisation head which acts as a flux guide portion and which in its extent at a location has the effective magnet, a permanent magnet or a separately excitable, in particular electrically excitable, magnet, the band to be magnetised can be introduced into the gap (air gap) of the for example C-shaped configuration of the magnetisation head and thus the magnetic flux can be introduced into the measuring scale to be magnetised, with a scatter effect which is as slight as possible.
In addition magnetic induction into or through the measuring scale can be altered by—mechanical or electrical—influencing of the magnet of the magnetisation head, even without having to move the magnetisation head away from the measuring scale.
To provide for the mechanical influencing effect, it is sufficient to move the mag
ASM Automation Sensorik Messtechnick & GmbH
Fulton Christopher W.
Head Johnson & Kachigian
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