Safe position measuring apparatus

Abstract

A scanning head for scanning a material measure on which markings with a period are formed periodically in the measuring direction includes at least two individual sensors configured to produce sensor signals by scanning the markings. The scanning head further includes a digital signal processing apparatus configured to produce at least one highly accurate output signal from the sensor signals. The scanning head is configured to output at least two different types of output signals. The at least two different types of output signals comprises at least one safe output signal and the at least one highly accurate output signal.

Claims

1. A scanning head for scanning a material measure on which markings with a period are formed periodically in a measuring direction, comprising: at least two individual sensors configured to produce sensor signals by scanning the markings; a digital signal processing apparatus connected to each of the at least two individual sensors, the digital signal processing apparatus configured to (i) receive the sensor signals from the at least two individual sensors and (ii) produce at least one digitally conditioned output signal based on the sensor signals using digital signal processing; at least one analog signal conditioning unit connected to at least one of the at least two individual sensors and including at least a signal amplifier and a signal demodulator, the at least one analog signal conditioning unit configured to (i) receive at least one of the sensor signals from the at least one of at least two individual sensors and (ii) produce at least one analog conditioned output signal based on the at least one of the sensor signals using analog signal processing; at least one digital output configured to connect to an evaluation unit, the at least one digitally conditioned output signal being outputted at the at least one digital output; and at least one analog output configured to connect to the evaluation unit, the at least one analog conditioned output signal being outputted at the at least one analog output, wherein the digital signal processing apparatus is connected to the signal demodulator and the signal amplifier and is configured to (i) receive an offset signal from the signal demodulator, (ii) identify a gain factor for operation of the signal amplifier using the offset signal, and (iii) adjust the signal amplifier to operate with the gain factor.

2. The scanning head according to claim 1, wherein the at least one analog conditioned output signal is not produced with digital signal processing.

3. The scanning head according to claim 1, wherein each of the at least two individual sensors includes two receiver coils and the two receiver coils are arranged beside one another in the measuring direction and connected in a differential manner.

4. The scanning head according to claim 1, wherein each of the at least two individual sensors has a transmitter coil.

5. A position measuring apparatus, comprising: a material measure on which markings are formed periodically in a measuring direction; and a scanning head including: at least two individual sensors configured to produce sensor signals by scanning the markings; a digital signal processing apparatus connected to each of the at least two individual sensors, the digital signal processing apparatus configured to (i) receive the sensor signals from the at least two individual sensors and (ii) produce at least one digitally conditioned output signal based on the sensor signals using digital signal processing; at least one analog signal conditioning unit connected to at least one of the at least two individual sensors and including at least a signal amplifier and a signal demodulator, the at least one analog signal conditioning unit configured to (i) receive at least one of the sensor signals from the at least one of at least two individual sensors and (ii) produce at least one analog conditioned output signal based on the at least one of the sensor signals using analog signal processing; at least one digital output configured to connect to an evaluation unit, the at least one digitally conditioned output signal being outputted at the at least one digital output; and at least one analog output configured to connect to the evaluation unit, the at least one analog conditioned output signal being outputted at the at least one analog output, wherein the digital signal processing apparatus connected to the signal demodulator and the signal amplifier and is configured to (i) receive an offset signal from the signal demodulator, (ii) identify a gain factor for operation of the signal amplifier using the offset signal, and (iii) adjust the signal amplifier to operate with the gain factor.

6. The position measuring apparatus according to claim 5, wherein the at least two individual sensors are at a distance from one another in the measuring direction and the distance is a multiple supplemented with a fraction of a period of the periodically formed markings.

7. The position measuring apparatus according to claim 6, wherein the fraction is a quarter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is schematically illustrated using an exemplary embodiment in the drawing and is described in detail below with reference to the drawing.

(2) FIG. 1 schematically shows a position measuring apparatus according to the disclosure in a preferred refinement.

DETAILED DESCRIPTION

(3) In the exemplary embodiments and in the figure, identical or identically acting parts are each provided with the same reference symbols. The elements illustrated here should not be considered as being true to scale, but rather individual elements may be illustrated on an excessively large scale for the sake of better understanding.

(4) FIG. 1 schematically illustrates a position measuring apparatus 10 in a preferred refinement. In the example shown, the position measuring apparatus 10 is in the form of an inductive measuring apparatus and comprises a scanning head 30 and a material measure 20 (illustrated on the left in FIG. 1) on which markings 22 are formed in the measuring direction 25. The markings 22 have a period 27, the length of a marking being)/2, as is the length of a web between two markings 22. The period 27 is therefore precisely . The material measure 20 is produced from a ferromagnetic sheet metal strip, for example. The markings 22 are simply rectangular holes or apertures in the sheet metal strip, for example.

(5) The scanning head 30 is designed to scan the material measure 20 and is movably mounted with respect to the material measure 20 in order to scan the latter. The scanning head 30 comprises two individual sensors 40, each of the individual sensors 40 in turn consisting of two receiver coils 33 which are interconnected in a differential manner. The two receiver coils 33 are surrounded by a transmitter coil 31 or the latter is assigned to said receiver coils.

(6) The two receiver coils 33 for each individual coil 40 are arranged beside one another in the measuring direction 25. The two individual coils 40 are at a distance 37 from one another which is a multiple of the period 27 supplemented with a fraction of the period 27; the fraction is preferably a quarter, by way of example. In the present case, the distance 37 corresponds to 2 of the period 27, that is to say 2.25. The length of a receiver coil 33 is substantially /2 and precisely one marking can therefore be covered thereby.

(7) The drawing also illustrates a digital signal processing apparatus 11 which is connected to the transmitter coils 31 which are connected in series. The digital signal processing apparatus 11 usually comprises A/D converters and FPGAs. During operation of the position measuring apparatus, a transmitter alternating current 32 (for example 100 kHz) is fed into the transmitter coils 31 and causes effective circulating currents in the transmitter coils 31. These currents each induce an AC voltage in the receiver coils 33. If a material measure 20 without markings (no holes, only ferromagnetic metal) were present, the magnitudes of these AC voltages would be the same but with an opposite sign, with the result that they would exactly cancel each other out. This effect is referred to as compensation. If this were dispensed with, the voltage at an individual sensor 40 would fluctuate, depending on a marking, by a signal offset, the magnitude of which is possibly greater than the fluctuations in the signal which are caused by the markings. This would make it considerably more difficult to evaluate the signals.

(8) However, if a receiver coil 33 is above a marking 22, the field produced by the transmitter coil 31 is influenced. If the receiver coils 31 arranged beside one another are influenced differently, a sensor signal is therefore produced, from which the position with respect to a marking can be inferred.

(9) If the scanning head 30 is moved with respect to the material measure 20, a sensor signal is to respectively produced in the individual sensors 40 or in their receiver coils 33, which sensor signal depends on the current position of the individual sensors 40 with respect to the markings 20. An analog cosine signal 36 is produced in one of the individual sensors 40, for example. Since the other individual sensor 40 is arranged in a manner offset by 2.25, in the measuring direction, the sensor signal produced there corresponds to an analog sine signal 35 and there is a phase shift of /4.

(10) The receiver coils 33 are connected to the digital signal processing apparatus 11, that is to say the two sensor signals 35, 36 are passed to this digital signal processing apparatus 11. Suitable means are used to produce at least one digitally conditioned output signal from the two sensor signals 35, 36, which output signal provides more accurate position and/or speed information, for example with a signal period of 40 m, than that provided by the two original sensor signals 35, 36 which have a signal period of 1 mm, for example. This at least one digitally conditioned output signal is output at at least one output 60. In the present example, a sine signal and a cosine signal are output as highly accurate output signals at the two outputs 60 and, from there, are made available to an evaluation unit 71, for example a PLC or a drive controller. The position and/or speed information is evaluated or further processed in the evaluation unit 71.

(11) In addition, the sensor signals, the analog cosine signal 36 and the analog sine signal 35, are also guided past the digital signal processing apparatus 11 via an analog signal conditioning unit 70 and are provided as safe output signals for the evaluation unit 71 at a respective output 61, 62. For this purpose, each of the individual sensors 40 or its two receiver coils 33 is/are connected to an analog demodulator 50. Each demodulated sensor signal is then supplied to the output 61 or 62 and therefore to the evaluation unit 71 via an analog amplifier 51.

(12) According to the example illustrated, each demodulated signal is additionally supplied, as an analog offset signal 52, to the digital signal processing apparatus 11 in which an analog gain factor 53 is determined therefrom, which gain factor is in turn supplied to the analog amplifier 51. Alternatively, autonomous digital offset control could also be provided. Downstream of the amplifier 51, the signal is therefore a cosine signal or a sine signal which has been conditioned in an analog manner.

(13) The signals which have been conditioned in an analog manner are the safe output signals and, although having lower positional accuracy than the digitally conditioned signals, can be used to ensure the provision of functional safety. The digitally conditioned signals can be used to provide highly accurate position and/or speed information.

LIST OF REFERENCE SYMBOLS

(14) 10 Position measuring apparatus

(15) 11 Digital signal processing apparatus

(16) 20 Material measure

(17) 22 Marking

(18) 25 Measuring direction

(19) 27 First distance

(20) 30 Scanning head

(21) 31 Transmitter coil

(22) 32 Transmitter alternating current

(23) 33 Receiver coil

(24) 35 Analog sine signal

(25) 36 Analog cosine signal

(26) 37 Second distance

(27) 50 Analog demodulator

(28) 51 Analog amplifier

(29) 52 Analog offset signal

(30) 53 Analog gain factor

(31) 60 Digital signal

(32) 61 Sine signal conditioned in an analog manner

(33) 62 Cosine signal conditioned in an analog manner

(34) 70 Signal conditioning unit

(35) 71 Evaluation unit