DE102013226203A1 - Offset compensated position measuring device - Google Patents

Abstract

The invention relates to a position measuring device having a measuring graduation (50) and a scanning head, which has evaluation electronics (80) and a sensor arrangement (20) for scanning the material measure, wherein a marking region (53) with markings (53) is provided on the material measure (50) in the measuring direction. 51), wherein the scanning head at least one receiver coil (40) and a compensation coil (41), which are connected in series and each having a transmitter coil (30, 31) is associated, wherein the receiver coil (40) and its associated Transmitter coil (30) are associated with the marking area (53), wherein the compensation coil (41) and its associated transmitter coil (31) are not associated with the marking area (53).

Description

The present invention relates to a position measuring device.

State of the art

Inductive sensor systems often work according to the transformer principle. An energized exciter structure generates an alternating magnetic field that can be detected by a receiver structure that is galvanically isolated. If external influence is exerted on the distribution of the magnetic field - e.g. by the presence of magnetically or electrically conductive materials - this has an effect on the measurable voltage of the receiver coil according to the law of induction. With this principle, a non-contact inductive measurement is possible.

Initially, the inductive measurement is strongly offset-related in principle. Namely, only the signal component by which the received signal is modulated by the external influences fluctuates as the useful signal. Typically, the proportion of the useful signal is only about 1 ‰ to max. 10% of the total signal. The rest of the signal is offset and i.d.R. undesirable.

For offset relief, a differential structure can be selected. For example, two receiver turns each can form a differential pair. The two windings are connected in series with opposite winding sense, so that as a measurable signal only the difference of the two coil signals is maintained, an offset is eliminated. Instead of a differential receiver coil, it is also conceivable to differentiate the transmitter coil in order to achieve offset freedom. As a result, the alternating magnetic field already acts differentially on the receiver coil. The received signal of a receiver coil is thus offset-free.

From the US Pat. No. 6,271,661 B1 For example, an inductive absolute position measuring system is known, which has as a material measure markings in a random order, wherein a mark can represent one of more than two information states. For scanning the material measure, individual sensors with differential receiver coils are used. There are two groups of individual sensors, which are offset by a fraction of the marking distances from each other. There is also a separate transmitter coil per group of individual sensors.

From the EP 1 164 358 B1 an inductive length measuring system is known in which pairs of receiver coils which are connected to one another in a different manner are provided for compensating for an offset.

The EP 2 502 030 B1 discloses an inductive measuring device in which there are two states for marks on a measuring scale, which are formed in two rows. In this case, a sensor comprises pairs of receiver coils which are connected together in a different manner, the individual coils being arranged in each case transversely to one another relative to the measuring direction. Each receiver coil pair is assigned a transmitter coil.

For offset relief, the measuring systems in the prior art always require differentially connected receiver coils in the sensor and markings in several rows for absolute position determination, which requires a relatively complex construction.

It is therefore desirable to provide a position measuring device in which a simpler material measure and simpler design and manufacture of the sensor can be achieved.

Disclosure of the invention

According to the invention, a position measuring device with the features of claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

A position measuring device according to the invention has a measuring standard, in particular an absolute measuring graduation, and a scanning head movably mounted relative to the material measure in a measuring direction, with evaluation electronics and a sensor arrangement for scanning the material measure. Markings are formed in the measurement direction in a marking region on the measuring direction and the scanning head has at least one receiver coil and a compensation coil which are connected in series and to each of which a transmitter coil is assigned, wherein the receiver coil and its associated transmitter coil are assigned to the marking region and wherein Compensation coil and its associated transmitter coil are not assigned to the marking area.

Advantages of the invention

The invention leads to a significant reduction of an offset voltage in the measurement signal. It was recognized that before the signal processing, no complete offset-freeing is necessary, but that it is sufficient to weaken an offset voltage in the measurement signal by such a large amount that the levels of useful signal and remaining Offset voltage are about the same order of magnitude. Thus, the (now in the level much smaller) received signal can be amplified analogously much higher. The actual useful signal component thus covers the input voltage range of a signal processing (in particular analog-to-digital conversion) much better, so that no very high ADC input resolution is necessary. A remaining offset voltage can be compensated by subsequent digital signal processing (either dynamically or by calibration).

Advantageously, the compensation coil and the transmitter coil associated therewith are associated with a mark-free area on the material measure which is free of markings. In particular, this mark-free region is formed parallel to the marking region on the material measure. As a result, compensation coil and receiver coil can be formed together in the sensor arrangement and the material measure is easy to manufacture. For this purpose, for example, only a slightly wider scale is necessary.

Preferably, the compensation coil is formed together with the receiver coil as a common coil, i. a part of the same coil is used as a compensation coil and another part as a receiver coil. In particular, this one coil then extends over both areas on the material measure. This allows a simple construction of the sensor, since no separate compensation coil is necessary.

Alternatively, the receiver coil is part of the sensor arrangement and the compensation coil part of the evaluation. In this case, two separate coils are necessary, but can be achieved by the spatial separation better offset reduction in the signal, since the compensation coil can not be influenced by arranged next to the compensation coil markings.

Advantageously, the receiver coil and the compensation coil associated transmitter coils are connected in series and connected to the same power source. This allows a simple circuit arrangement.

Alternatively, the said transmitter coils are connected to different current sources, in particular the current source, from which the transmitter coil associated with the transmitter coil is supplied with power, adjustable to reduce an offset voltage in a measurement signal. This allows a better offset reduction can be achieved.

It is advantageous if the receiver coil, the compensation coil and their associated transmitter coils are connected so that a voltage induced in the compensation coil by a magnetic field reduces or compensates for a voltage induced in the receiver coil by the same magnetic field. By such a vote of the individual coils successive another offset minimization can already be reduced in advance by the coils per se.

Advantageously, at least two receiver coils are included in the scanning head, each receiver coil being associated with a compensation coil and corresponding to transmitter coils. This allows multiple markers to be detected simultaneously and the coils can be permanently interconnected.

Alternatively, the scanning head comprises only one compensation coil, which is in each case alternately connectable to the compensation coil by means of a multiplexer, which in particular belongs to evaluation electronics. As a result, the sensor arrangement can be made simpler and more compact.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

figure description

1 schematically shows a sensor arrangement and an evaluation for a position measuring device according to the invention in a preferred embodiment.

2 schematically shows a sensor arrangement and an evaluation for a position measuring device according to the invention in a further preferred embodiment.

3 schematically shows a sensor arrangement and an evaluation for a position measuring device according to the invention in a further preferred embodiment.

4 schematically shows a sensor arrangement and an evaluation for a position measuring device according to the invention in a further preferred embodiment.

Detailed description of the drawing

In 1 are schematically a sensor arrangement 20 and an evaluation 80 a scanning head of a position measuring device according to the invention shown in a preferred embodiment.

The sensor arrangement 20 includes by way of example a receiver coil 40 and a transmitter coil associated therewith 30 , The evaluation electronics 80 includes a compensation coil 41 and a transmitter coil associated therewith 31 , receiver coil 40 and compensation coil 41 are connected in series and to an amplifier 81 connected. The two transmitter coils 30 . 31 are also connected in series and to a power source 85 connected. The compensation coil 41 together with the transmitter coil 31 may, for example, be designed as a so-called compensation transformer. This is possible, for example, in the form of a printed circuit board with planar coils formed thereon. Likewise, the system works from receiver coil 40 and associated transmitter coil 30 according to the transformer principle. The winding sense of the two transformers are indicated by dots. The receiver coil and the compensation coil are connected in series, that in the compensation coil 41 from the transmitter coil 31 induced voltage in the receiver coil 40 from the transmitter coil 30 induced voltage reduced.

The two components sensor arrangement 20 and evaluation electronics 80 are spatially separated from each other in real design. The sensor 20 is near a material measure, preferably made of ferromagnetic metal, are formed on the markings along. Such markings may be formed, for example, as holes in the material measure. The evaluation electronics 80 is, for example, above the sensor array 20 but within the scanning head, so that there is no spatial proximity to the measuring scale.

In the excitation coils 30 . 31 When operating the position measuring device in each case a transmitter alternating current (eg 100 kHz) by means of the power source 85 fed, which causes effective circulating currents. In the receiver coil 40 or the compensation coil 41 This will induce an AC voltage. If no material measure were present, these alternating voltages would be equal in magnitude, however, with opposite sign, so that they cancel each other exactly. Markers cause in the receiver coil 40 changed AC voltages, which together with the compensation coil generates a useful signal, the amplifier 81 can be processed accordingly.

The sensor arrangement 20 but can also have multiple receiver coils 40 , Compensation coils 41 and associated transmitter coils 30 . 31 include, depending on the preferred application, ie how many marks on the absolute measuring scale should be concealed and / or read out at the same time.

In 2 are schematically a sensor arrangement 20 and an evaluation 80 a scanning head shown in a further preferred embodiment.

In essence, the design agrees with that of 1 match, except that the transmitter coils 30 . 31 from different power sources 86 . 85 be supplied. Although two current sources are needed here, the compensation, which corresponds to offset minimization, can be adjusted more precisely, ie the signals can be optimally matched to one another.

In 3 are schematically a sensor arrangement 20 and an evaluation 80 a scanning head shown in a further preferred embodiment.

The sensor arrangement 20 exemplifies several receiver coils 40 and a compensation coil 41 , The evaluation electronics 80 includes an amplifier 81 as well as a multiplexer 82 and a power source 85 , The receiver coils 40 and the compensation coil 41 are each transmitter coils 30 . 31 assigned, which are connected in series and to a power supply 85 are connected.

The compensation coil 41 can by means of the multiplexer 82 alternating with one of the receiver coils 40 connected in series and with an amplifier 81 get connected. Thus, a compensation is made possible for a receiver coil, which are therefore read out alternately. The operating principle of the compensation is the same as with the previously mentioned position measuring devices. The compensation coil 41 and the associated transmitter coil 31 are arranged spatially distant from the marks of the material measure, so that they are not affected by these.

In 4 are schematically a material measure 50 and a sensor arrangement 20 one shown in a further preferred embodiment.

The measuring standard 50 has two parallel areas 53 . 54 on, being in a marking area 53 in measuring direction 11 marks 51 the length λ are formed. In a mark free area 54 There are no markings. The marks 51 represent one of two possible states of information, depending on whether at one point a mark, for example a hole, is present or not. The different Information states are denoted by 0 or 1 under the material measure.

The sensor arrangement 20 comprises three planar layers of electrical conductors, which are arranged opposite to each other, wherein they are electrically insulated from each other. The layer shown on the left comprises, for example, three receiver coils 40 and three compensation coils 41 , wherein each one receiver coil and the associated compensation coil as parts of the same coil, each having a pitch λ in the measuring direction 11 is long, educated. With the reference symbols a, b, c are the positions of the three receiver coils 40 and compensation coils 41 within the sensor array 20 characterized. The receiver coils 40 and compensation coils 41 can each be formed as a single turn in a layer or layer of a multilayer or multilayer arrangement.

Furthermore, the sensor arrangement comprises 20 transmitter coils 30 . 31 , which are designed here as so-called. Mäanderwindungen. Two meander turns each 30a and 30 b or 31a and 31b together form the transmitter coils 30 and 31 wherein the two meander turns are formed in two different layers of the multilayer assembly. For the sake of clarity, the two meander turns 30a . 30b respectively. 31a . 31b shown side by side, but in practical execution are 30a and 30b respectively. 31a and 31b one above the other. The exact position is indicated by the reference symbols a, b, c. Likewise, the meander turns and thus the transmitter coils 30 . 31 in practical execution above or below the receiver coils 40 and compensation coils 41 , The exact position is again indicated by the reference symbols a, b, c. Each of the meander turns 30a . 30b . 31a . 31b alternately has two right-hander turns and two left-hander turns, which are squared 90 ° curves. There are straight sections between the curves.

Through vias 33 the meander turns of the two layers are each electrically connected to each other and by means of connections 34 the meander windings and thus the transmitter coils are connected to a power supply.

The operation of the position measuring device is otherwise substantially the same as that of the other previously shown absolute position measuring devices in the 1 to 3 , An influence on the receiver coils 40 induced voltage is carried by the markers 51 by influencing the alternating magnetic field generated by the transmitter coils. The compensation coils 41 are not affected because at their assigned location on the material measure 50 , the mark-free area 54 , no marks are formed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US Pat. No. 6,271,661 B1 [0005]
• EP 1164358 B1 [0006]
• EP 2502030 B1 [0007]

Claims (12)

Position measuring device with a material measure ( 50 ) and a scanning head, the evaluation electronics ( 80 ) and a sensor arrangement ( 20 ) for scanning the material measure, wherein on the material measure ( 50 ) in the measuring direction a marking area ( 53 ) with markings ( 51 ), wherein the scanning head at least one receiver coil ( 40 ) and a compensation coil ( 41 ), which are connected in series and each with a transmitter coil ( 30 . 31 ), wherein the receiver coil ( 40 ) and its associated transmitter coil ( 30 ) the marking area ( 53 ), the compensation coil ( 41 ) and its associated transmitter coil ( 31 ) not the marking area ( 53 ) assigned. Position measuring device according to claim 1, wherein the compensation coil ( 41 ) a label-free area ( 54 ) is assigned to the material measure which is free of markings. Position measuring device according to claim 2, wherein the receiver coil ( 40 ) and the compensation coil ( 41 ) are formed together as a coil. Position measuring device according to claim 3, wherein the receiver coil ( 40 ) and the compensation coil ( 41 ) associated transmitter coils ( 30 . 31 ) have an opposite sense of winding. Position measuring device according to claim 1, wherein the receiver coil ( 40 ) Part of the sensor arrangement ( 20 ) and the compensation coil ( 41 ) Part of the evaluation electronics ( 80 ). Position measuring device according to one of the preceding claims, wherein the receiver coil ( 40 ) associated with transmitter coil ( 30 ) and the compensation coil ( 41 ) associated with transmitter coil ( 31 ) are connected in series and connected to the same power source. Position measuring device according to one of claims 1 to 5, wherein the receiver coil ( 40 ) associated with transmitter coil ( 30 ) and the compensation coil ( 41 ) associated with transmitter coil ( 31 ) are connected to different power sources. Position measuring device according to claim 7, wherein the current source is the one of the compensation coil ( 41 ) associated transmitter coil ( 31 ) is adjustable to reduce an offset voltage in a measurement signal. Position measuring device according to one of the preceding claims, wherein the compensation coil ( 41 ) and its associated transmitter coil ( 31 ) form a compensation transformer. Position measuring device according to one of the preceding claims, wherein the receiver coil ( 40 ), the compensation coil ( 41 ) and their associated transmitter coils ( 30 . 31 ) are switched so that one in the compensation coil ( 41 ) induced voltage by a magnetic field in the receiver coil ( 40 ) is reduced by the same magnetic field induced voltage. Position measuring device according to one of the preceding claims, wherein the scanning head at least two receiver coils ( 40 ), each with a compensation coil ( 41 ), each of the receiver coils ( 40 ) and each of the compensation coils ( 41 ) one transmitter coil each ( 30 . 31 ) assigned. Position measuring device according to one of claims 1 to 10, wherein the scanning head at least two receiver coils ( 40 ), which by means of a multiplexer ( 82 ) alternately with the compensation coil ( 41 ) are connectable, each of the receiver coils ( 40 ) and the compensation coil ( 41 ) one transmitter coil each ( 30 . 31 ) assigned.

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