SIGNAL PROCESSING CIRCUIT FOR MEASURING MACHINE

Abstract

There is provided a signal processing circuit, which improves a signal SN ratio, for a measuring machine. A sensor uses two or more reference signals processed so as to have a mutual predetermined phase difference. The signal processing circuit includes a phase correcting circuit which removes an offset due to a phase shift between the two or more reference signals. The phase correcting circuit includes an offset detecting unit which adds the two or more reference signals and extracts the offset, and a correction processing unit which removes the offset from a sensor signal.

Claims

1. A signal processing circuit, which receives, as measurement data, a sensor signal from a sensor using two or more reference signals processed so as to have a mutual predetermined phase difference, for a measuring machine, the signal processing circuit comprising: a phase correcting circuit configured to remove an offset due to a phase shift between the two or more reference signals, wherein the phase correcting circuit comprises: an offset detecting unit configured to add the two or more reference signals and extract the offset; and a correction processing unit configured to remove the offset from the sensor signal.

2. The signal processing circuit for the measuring machine according to claim 1, wherein the offset detecting unit and the correction processing unit function as an adder/subtractor circuit which includes a common operational amplifier.

3. The signal processing circuit for the measuring machine according to claim 1 further comprising: a first amplifier disposed so as to follow the phase correcting circuit; a plurality of processing circuits disposed so as to follow the first amplifier; and a second amplifier disposed so as to follow the plurality of processing circuits, wherein a gain of the first amplifier is set to a maximum value which the plurality of processing circuits tolerates as much as possible.

4. A measuring machine comprising: a sensor configured to use two or more reference signals processed so as to have a mutual predetermined phase difference; and the signal processing circuit for the measuring machine according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a diagram illustrating a signal processing circuit, which processes a sensor signal, for a measuring machine;

[0046] FIG. 2 is a diagram explaining an offset voltage due to a phase shift of a reference signal;

[0047] FIG. 3 is a diagram illustrating a signal processing circuit according to a first exemplary embodiment of the present invention;

[0048] FIG. 4 is a diagram illustrating a specific configuration example of a phase correcting circuit; and

[0049] FIG. 5 is a diagram illustrating a modified example 1.

DETAILED DESCRIPTION

[0050] An embodiment of the present invention is illustrated and is described with reference to the reference signs attached to the elements of the drawings.

First Exemplary Embodiment

[0051] FIG. 3 a diagram illustrating a signal processing circuit 100 according to a first exemplary embodiment of the present invention.

[0052] A feature of the present exemplary embodiment is to dispose a phase correction circuit 200 so as to precede a first amplifier 110. In other words, a sensor signal from a sensor 500 is subjected to correction processing by the phase correction circuit 200 and then input to the first amplifier 110.

[0053] FIG. 4 is a diagram illustrating a specific configuration example of the phase correction circuit 200.

[0054] The phase correction circuit 200 includes a sensor signal input unit 210, an offset detecting unit 220, and a correction processing unit 230.

[0055] The sensor signal input unit 210 is connected to the sensor signal output end of the sensor 500, and receives a sensor signal S.sub.EO from the sensor 500. The sensor signal input unit 210 outputs the received sensor signal S.sub.EO to the correction processing unit 230.

[0056] Here, the sensor signal S.sub.EO varies according to the displacement of the core 530. However, when there is a phase shift between a first reference signal SA1 and a second reference signal SA2, the signal includes the offset due to the phase shift (for example, see FIG. 2).

[0057] Note that, the sensor signal input unit 210 is a non-inverting amplifier circuit (voltage follower) having a one-time gain, and is what is called a buffer to match the impedance with that of other circuits.

[0058] Furthermore, a coupling capacitor 211 is disposed between the sensor signal input unit 210 and the correction processing unit 230 to remove the DC level.

[0059] The offset detecting unit 220 includes two input ends and an adder circuit 221. The two input ends are referred to as a first input end and a second input end.

[0060] The first input end is connected with the first reference signal input end of the sensor 500. In other words, the first reference signal SA1 is input to the first input end similarly to the sensor 500.

[0061] The second input end is connected with the second reference signal input end of the sensor 500. In other words, the second reference signal SA2 is input to the second input end similarly to the sensor 500.

[0062] The first input end and the second input end are connected with the adder circuit 221. Note that, a coupling capacitor 222 to remove the DC level is each disposed between the first input end and the adder circuit 221, and between the second input end and the adder circuit 221. The first reference signal SA1 and the second reference signal SA2 are added by the adder circuit 221.

[0063] When the first reference signal SA1 has an ideal phase opposite to the phase of the second reference signal SA2, the output from the adder circuit 221 is to be constantly 0 V.

[0064] When there is a phase shift between the first reference signal SA1 and the second reference signal SA2, the output from the adder circuit 221 is to be a signal equivalent to the offset due to the phase shift (see FIG. 2). Thus, the output signal from the adder circuit 221 (the offset detecting unit 220) is referred to as an offset signal So. The offset signal So from the adder circuit 221 is input to the correction processing unit 230.

[0065] The correction processing unit 230 performs correction processing to remove the offset from the sensor signal S.sub.EO by removing the offset signal So from the sensor signal S.sub.EO.

[0066] Thus, a sensor signal S.sub.E from which the offset is removed is obtained.

[0067] If the sensor itself includes an offset, the signal processing circuit 100 according to the present embodiment can remove the offset from the sensor signal S.sub.EO.

[0068] Thus, when a sensor 500 is selected, the sensor 500 having high quality is not necessarily used, and it is possible to reduce the cost of the measuring machine. Furthermore, since the sensor signal SE without an offset is obtained, the amplification factor (GA) of the first amplifier 110 can be ideally increased.

[0069] For example, in such a manner that the gain of the first amplifier 110 is increased to be 100 times and the gain of the second amplifier 130 is increased to be 5 times, the gain of the first amplifier 110 is sufficiently increased.

Modified Example 1

[0070] A modified example 1 is illustrated in FIG. 5.

[0071] In the modified example 1, the offset detecting unit 220 and the correction processing unit 230 have a common operational amplifier, and an effect similar to the first exemplary embodiment can be obtained.

[0072] The offset detecting unit 220 and the correction processing unit 230 are integrated and function as an adder/subtractor circuit 240.

[0073] With this configuration, it is possible to obtain an effect similar to the first exemplary embodiment, and to miniaturize the signal processing circuit since the components are reduced.

[0074] Note that, the present invention is not limited to the above embodiment, and can be appropriately changed without deviating from the scope.

[0075] The differential inductance has been exemplified as the sensor, but a type of the sensor is not especially limited.

[0076] The sensor is only required to use two reference signals each having a phase opposite to each other.

[0077] Alternatively, the sensor is only required to use a plurality of reference signals processed so as to have a mutual predetermined phase difference instead of the two reference signal each having a phase opposite to each other.