JP2013222402A - Offset adjustment circuit and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable offset adjustment even when a time constant of a filter for applying filtering to an input signal is made small in order to deal with a control system that requires fast response.SOLUTION: An offset adjustment circuit 1, in the offset adjustment mode, uses an LPF 4 having a time constant for offset adjustment, in addition to an LPF12 having a time constant that reflects responsiveness of a control system, to filter an adjustment signal for offset adjustment and stores a value of the filtered signal as an offset value in a memory 14. A value for offset adjustment, which is not related to responsiveness of the control system, is preset as the time constant of the LPF4. Such an arrangement produces a stable offset value which is not affected by white noise and the like generated inside and outside a control device 20 even when the time constant of the LPF12 for filtering an input signal is small.

Description

  The present invention relates to a circuit and a program for adjusting an offset of an input signal in an apparatus that inputs an analog signal from a sensor or the like provided in a control target, converts the input analog signal into a digital signal, and performs predetermined processing.

  Conventionally, in a control system that controls a control target such as a motor to cause an actuator connected to the motor or the like to perform a desired operation, a control amount of an analog signal is input from a sensor or the like provided on the control target and input. There is known a control device that converts a control amount of an analog signal into a digital signal, calculates an operation amount so that the control amount becomes a predetermined target value, and outputs the operation amount of the operation result to a control target. In general, an analog signal input by such a control apparatus is accompanied by an offset due to an environment such as an ambient temperature where the sensor is installed, an inherent characteristic of the sensor, aging, or the like. For this reason, the control device is provided with an offset adjustment circuit that adjusts an offset included in the input signal and excludes the offset from the input signal.

  FIG. 3 is a block diagram showing a configuration of a conventional offset adjustment circuit. The offset adjustment circuit 10 sets an offset of the input signal in the offset adjustment mode before operating the control device including the offset adjustment circuit 10 in the normal mode. The offset adjustment circuit 10 includes a subtractor 11, an LPF (Low Pass Filter) 12, a SW (Switch) 13, and a memory 14.

  The operation mode of the control device including the offset adjustment circuit 10 includes an offset adjustment mode and a normal mode. The offset adjustment mode is an operation mode for setting an offset of the input signal before the control device is operated in the normal mode, and the offset value is stored in the memory 14. The normal mode is an operation mode for the control device to realize the original control, the offset value is read from the memory 14, and the offset value is subtracted from the value of the signal after filtering the input signal. The signal of the subtraction result is used for control.

  When the operator performs an operation to set the control device to the offset adjustment mode, the SW 13 is turned on, and an adjustment signal for offset adjustment (a reference signal from a sensor that should originally be Vin = 0) from a sensor or the like. ) Is supplied to the offset adjustment circuit 10. The LPF 12 receives an adjustment signal for offset adjustment, performs a filter process on the adjustment signal, and outputs a signal after the filter process to the memory 14 via the SW 13. As a result, the offset value is stored in the memory 14.

  On the other hand, when the operator performs an operation for setting the control device to the normal mode after the offset setting in the offset adjustment mode is completed, the SW 13 is turned off. The LPF 12 performs a filtering process on an input signal from a sensor or the like, and outputs the signal after the filtering process to the subtractor 11. The subtractor 11 receives the filtered signal from the LPF 12, reads the offset value from the memory 14, subtracts the offset value from the filtered signal value, and outputs a subtraction result signal (Vout). In this way, the offset adjustment circuit 10 subtracts the offset value from the value of the signal obtained by performing the filtering process on the input signal, and a signal resulting from the subtraction is obtained.

  In addition, it is not a technical field in which an input analog signal is converted into a digital signal and predetermined processing is performed, but in the field of waveform shaping, a circuit that switches a time constant is known to compensate for an input signal with an offset. (See Patent Document 1). The compensation circuit includes a low-pass filter or a high-pass filter, a switch, and the like. The time constant of the filter is switched by setting the switch to ON in the setting mode and setting the switch to OFF in the normal mode. Thereby, the threshold value for reliably distinguishing the logical value of the bit sequence in the digitally modulated signal can be set appropriately.

Special table 2003-533132 gazette

  When the control device including the offset adjustment circuit 10 shown in FIG. 3 controls a highly responsive control object such as when controlling a motor at high speed, that is, when a quick response is required as a control system. Therefore, it is necessary to reduce the time constant of the LPF 12 provided in the offset adjustment circuit 10.

  However, when setting the offset in the offset adjustment mode, the adjustment signal supplied to the offset adjustment circuit 10 usually varies finely due to white noise generated outside and inside the control device. For this reason, in the offset adjustment circuit 10 including the LPF 12 having a small time constant, the output signal of the LPF 12 also varies finely, and the offset value stored in the memory 14 changes according to the timing, resulting in an unstable offset value. End up.

  In this case, in order to eliminate the influence of white noise or the like, it is assumed that the time constant of the LPF 12 is increased. However, since the control system requires a quick response, the time constant cannot be increased. Therefore, the conventional offset adjustment circuit 10 shown in FIG. 3 has a problem that the offset value stored in the memory 14 is not constant, so that stable offset adjustment cannot be performed.

  Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to cope with a control system that requires a quick response, so that the time constant of a filter that filters an input signal is small. Even if it exists, it is providing the offset adjustment circuit and program which can implement | achieve stable offset adjustment.

  In order to achieve the above object, an offset adjustment circuit according to the present invention performs a filter process on an input signal with a first time constant, subtracts an offset value from the value of the signal after the filter process, and generates a subtraction result signal. In an offset adjustment circuit included in a device that performs predetermined processing based on the memory, a memory that stores the offset value, a first filter that performs a filtering process on the input signal with a first time constant, and the memory A subtracter that reads an offset value from the first filter and subtracts the offset value from a signal value after filtering by the first filter, a switch that performs an offset adjustment for storing the offset value in the memory, and the offset adjustment A second filter that performs a filtering process with a second time constant for the first time constant, and at the time of the offset adjustment, The filter inputs a predetermined adjustment signal as an input signal, performs a filter process on the adjustment signal with a first time constant, and the second filter performs a filter process with the first filter. A signal is input via the switch, the input signal is filtered with a second time constant, and the value of the filtered signal is stored in the memory as an offset value. It is characterized by.

  The offset adjustment circuit according to the present invention is characterized in that the second time constant is set to a value larger than the first time constant.

  Furthermore, an offset adjustment program according to the present invention causes a computer to function as the offset adjustment circuit.

  As described above, according to the present invention, in offset adjustment, in addition to a filter having a time constant corresponding to the control system, an offset value is obtained using a filter having a time constant for offset adjustment. Therefore, stable offset adjustment can be realized.

It is the schematic which shows the whole structure containing the offset adjustment circuit by embodiment of this invention. It is a flowchart which shows the process of an offset adjustment circuit. It is a block diagram which shows the structure of the conventional offset adjustment circuit.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an overall configuration including an offset adjustment circuit according to an embodiment of the present invention. The control device 20 includes an offset adjustment circuit 1, an A / D converter 2, and a processing unit 3. A control amount is input from a sensor or the like provided on a control target such as a motor, and the control amount is a predetermined target. The operation amount is calculated so as to be a value, and the operation amount as a calculation result is output to the control target. By such a feedback control system, an actuator or the like (not shown) connected to a control target such as a motor performs a desired operation.

  The A / D converter 2 inputs a control amount of an analog signal from a sensor or the like provided in the control device 20, and converts the control amount of the analog signal into a control amount of a digital signal. The control amount of the converted digital signal is output to the offset adjustment circuit 1.

[Configuration of offset adjustment circuit]
The offset adjustment circuit 1 includes a subtractor 11, LPF 12, SW 13, LPF 4, and memory 14. Comparing the conventional offset adjustment circuit 10 shown in FIG. 3 with the offset adjustment circuit 1 shown in FIG. 1, both offset adjustment circuits 1 and 10 are provided with a subtractor 11, LPF 12, SW 13, and memory 14. Are the same. On the other hand, the offset adjustment circuit 1 is different in that an LPF 4 is provided between the SW 13 and the memory 14 in addition to the configuration of the conventional offset adjustment circuit 10.

  As with the conventional offset adjustment circuit 10, the operation mode of the control device 20 includes an offset adjustment mode and a normal mode. The operation mode is switched by the SW 13 according to the operator's operation. When SW13 is set to ON, the operation mode is an offset adjustment mode, and when SW13 is set to OFF, the operation mode is a normal mode. For example, the SW 13 is set to ON or OFF by a trigger from the host system according to the operator's operation.

  Regardless of whether the operation mode is the offset adjustment mode or the normal mode, the LPF 12 receives a digital signal from the A / D converter 2 and performs a filtering process on the input digital signal with a predetermined time constant. Outputs the processed signal. When the operation mode is the offset adjustment mode, the LPF 12 inputs an adjustment signal from the A / D converter 2, performs a filter process on the adjustment signal with a predetermined time constant, and sends the signal after the filter process to the SW 13. To the LPF 4 and to the subtractor 11.

  Further, when the operation mode is the normal mode, the LPF 12 performs a filtering process on the input signal from the A / D converter 2 with the same predetermined time constant as described above, and the filtered signal is subtracted by the subtractor 11. Output to. In this case, since the SW 13 is in an off state, the signal after the filter processing is not output to the LPF 4.

  Here, when a fast response is required as a predetermined time constant in the LPF 12 as a control system configured by the control device 20 and the control target 30, a small value is set in advance as the time constant of the LPF 12. As a result, an output signal that closely follows the change in the input signal is supplied to the processing unit 3 via the subtractor 11.

  When the operation mode is the offset adjustment mode, the LPF 4 inputs a signal after the filtering process by the LPF 12 from the LPF 12 via the SW 13, performs a filtering process on the input signal with a predetermined time constant, and performs the filtering process. Are stored in the memory 14. As a result, the offset value is stored in the memory 14.

  Here, the predetermined time constant in the LPF 4 has an offset adjustment so that the signal after the filter processing by the LPF 4 becomes a stable signal so as not to be affected by white noise or the like regardless of the response of the control system. A value for this is preset. For example, when a fast response is required as the control system, the time constant of LPF 4 is set to a value larger than the time constant of LPF 12.

  Regardless of whether the operation mode is the offset adjustment mode or the normal mode, the subtracter 11 inputs the signal after filtering from the LPF 12, reads data from the memory 14, and subtracts the offset value from the control amount of the signal after filtering. Then, the signal of the subtraction result is output to the processing unit 3.

  When the operation mode is the offset adjustment mode, the processing unit 3 does not perform processing even if a signal is not input from the offset adjustment circuit 1 or a signal is input from the offset adjustment circuit 1. Further, when the operation mode is the normal mode, the processing unit 3 inputs a signal from the offset adjustment circuit 1 and subtracts a preset target value from the value of the input signal, for example, and the deviation of the subtraction result is 0. PID or the like is calculated so that the operation amount is obtained, and the operation amount of the calculation result is output to the control target 30. In the feedback control system configured by the control device 20 and the control target 30, control is performed so that the control amount indicating the value of the input signal of the sensor or the like provided in the control target 30 becomes the target value in the normal mode. The actuator or the like connected to the control object 30 is caused to perform a desired operation.

[Offset adjustment circuit processing]
Next, processing of the offset adjustment circuit 1 shown in FIG. 1 will be described. FIG. 2 is a flowchart showing the processing of the offset adjustment circuit 1. Along with the setting of the operation mode for the control device 20 by the operator, the offset adjustment circuit 1 determines whether the operation mode set by the operator is the offset adjustment mode or the normal mode (step S201).

  If it is determined in step S201 that the operation mode is the offset adjustment mode (step S201: offset adjustment mode), the offset adjustment circuit 1 sets the SW 13 to ON (step S202). Then, the offset adjustment circuit 1 inputs an adjustment signal for offset adjustment from the controlled object 30 (step S203), and the LPF 12 has a predetermined time constant reflecting the response of the control system to the adjustment signal. Filter processing is performed (step S204). Then, the offset adjustment circuit 1 performs filter processing with a predetermined time constant for offset adjustment on the signal after the filter processing by the LPF 12 in the LPF 4 (step S205).

  The offset adjustment circuit 1 determines whether or not a predetermined period (offset adjustment period) has elapsed after setting the SW 13 to ON (step S206). If it is determined in step S206 that the predetermined period has not elapsed (step S206: N), the offset adjustment circuit 1 waits for the predetermined period to elapse. On the other hand, when it is determined in step S206 that the predetermined period has elapsed (step S206: Y), the offset adjustment circuit 1 stores the value of the signal after filtering by the LPF 4 in the memory 14 as an offset value (step S207).

  On the other hand, when it is determined in step S201 that the operation mode is the normal mode (step S201: normal mode), the offset adjustment circuit 1 sets SW13 to OFF (step S208). The offset adjustment circuit 1 receives a signal from the control target 30 (step S209), and the LPF 12 performs a filtering process on the input signal with a predetermined time constant reflecting the response of the control system ( Step S210). Then, the offset adjustment circuit 1 reads the offset value from the memory 14 (Step S211), subtracts the offset value from the signal value after the filter processing by the LPF 12 (Step S212), and outputs the signal after the subtraction to the processing unit 3. (Step S213).

  As described above, according to the offset adjustment circuit 1 according to the embodiment of the present invention, in the offset adjustment mode, in addition to the LPF 12 having the time constant reflecting the response of the control system, the offset adjustment circuit 1 has the time constant for offset adjustment. The LPF 4 is used to filter the adjustment signal for offset adjustment, and the value of the signal after the filter processing is stored in the memory 14 as an offset value. As a result, the offset value becomes a value that has been filtered with a time constant for offset adjustment that has nothing to do with the response of the control system, and thus is a stable value that is not affected by white noise or the like. Therefore, since the LPF 12 having a time constant reflecting the response of the control system is used in the normal mode, the response of the signal corresponding to the control system is not impaired, and a stable offset adjustment is realized in the offset adjustment mode. can do.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the technical idea thereof. For example, in FIG. 1, the offset control circuit 1 provided in the control device 20 has been described by taking the feedback control system as an example. However, the present invention measures not only the control device 20 used in the feedback control system but also the temperature and the like. The present invention is also applicable to a device that converts an analog signal into a digital signal and performs predetermined processing on the converted digital signal, such as a measurement device.

  Note that a normal computer can be used as the hardware configuration of the control device 20 including the offset adjustment circuit 1 according to the embodiment of the present invention. The control device 20 including the offset adjustment circuit 1 is configured by a computer including a CPU, a volatile storage medium such as a RAM, a non-volatile storage medium such as a ROM, an interface, and the like. Each function of the subtractor 11, LPF 12, SW 13 and LPF 4 constituting the offset adjustment circuit 1 provided in the control device 20 is realized by causing the CPU to execute a program describing these functions. These programs can also be stored and distributed in a storage medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), optical disk (CD-ROM, DVD, etc.), semiconductor memory, etc. You can also send and receive.

1,10 Offset adjustment circuit 2 A / D converter 3 Processing unit 4,12 LPF
11 Subtractor 13 SW
14 Memory 20 Control device 30 Control target

Claims (3)

In an offset adjustment circuit included in a device that performs a filtering process on an input signal with a first time constant, subtracts an offset value from the value of the signal after the filtering process, and performs a predetermined process based on the signal of the subtraction result,
A memory in which the offset value is stored;
A first filter that filters the input signal with a first time constant;
A subtracter that reads an offset value from the memory and subtracts the offset value from a value of a signal after filtering by the first filter;
A switch for performing offset adjustment for storing an offset value in the memory;
A second filter that performs filtering with a second time constant for adjusting the offset,
During the offset adjustment,
The first filter inputs a predetermined adjustment signal as an input signal, performs a filtering process on the adjustment signal with a first time constant,
The second filter inputs the signal filtered by the first filter through the switch, filters the input signal with a second time constant, and filters the filter. An offset adjustment circuit, wherein the value of the processed signal is stored in the memory as an offset value. The offset adjustment circuit according to claim 1,
An offset adjustment circuit characterized in that the second time constant is set to a value larger than the first time constant.   An offset adjustment program for causing a computer to function as the offset adjustment circuit according to claim 1.

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