JP6320144B2 - Weight indicator - Google Patents

Description

  The present invention relates to a weight indicator provided in a weighing device that measures the weight of an object to be weighed.

  2. Description of the Related Art Conventionally, weighing devices such as weight type quantitative filling machines and vehicle weighing devices are equipped with a weight indicator that calculates the weight value of an object to be measured based on a load signal from a load detector and displays the weight value and the like. (For example, refer to Patent Document 1).

  Noise (natural vibration noise) due to the natural vibration of the weighing device itself, noise due to basic vibration (basic vibration noise) received from the installation location (foundation) of the weighing device, etc. are superimposed on the load signal. Therefore, a digital filter is used in the weight indicator in order to remove noise superimposed on the load signal (see, for example, Patent Documents 1 and 2).

JP 2006-78410 A JP 2003-207387 A

  In Patent Documents 1 and 2, a moving average filter is used. That is, a filter format (moving average filter) is determined, and a frequency of noise is substantially selected and noise of that frequency is removed.

  However, even with the same weighing device, if the load load conditions are different, the state of vibration noise superimposed on the load signal is different. For example, if the weighing device is a vehicle weighing device that measures the vehicle weight even when the vehicle is traveling at a low speed on the weighing table, the natural vibration noise is a sine with a constant amplitude when the vehicle moves on the weighing table. Since the amplitude changes irregularly instead of the wave, in such a case, even if the natural vibration noise is removed in accordance with the frequency, the amplitude of the noise cannot be completely attenuated.

  In addition, the weight indicator is often used in various weighing devices. For example, different types of weighing devices such as a weight type metering filling machine and a track scale have different frequencies such as natural vibration noise. In addition, even in the same type of weighing device, the frequency of natural vibration noise and the like is different if the size is different. In addition, the frequency of basic vibration noise and the like varies depending on the installation location of the weighing device.

  As described above, the configurations of Patent Documents 1 and 2 are insufficient to appropriately remove various noises and realize a highly versatile weight indicator.

  The present invention has been made in order to solve the above-described problems, and it is possible to appropriately remove various noises that differ depending on the installation location of the weighing device, the type of the weighing device, etc. It is intended to provide.

  In order to achieve the above object, a weight indicator according to an aspect of the present invention is provided in a weighing device for weighing the object to be weighed, and is used for weighing the object to be weighed. Filter processing means for filtering the digital load signal obtained by A / D converting the output signal of the load sensor; and weight calculation means for calculating the weight of the object to be measured based on the filtered digital load signal. A weight indicator that selects one or a plurality of filter types from a plurality of pre-stored different filter types and inputs a filter constant that defines the characteristics of the filter configured by the selected filter type The filter processing means comprising: setting means; and one filter whose filter type and filter constant are determined by the filter setting means Or, and a filter forming means for forming said filtering means a plurality of filters Filter Format and filter constants defined formed by cascade connection by the filter setting unit.

  According to this configuration, for one or a plurality of filters constituting the filter processing means, a filter format is selected from a plurality of different filter formats, and a filter constant for the selected filter format is arbitrarily set. Therefore, it is possible to configure filter processing means that can appropriately remove various noises depending on the installation location of the weighing device, the type and size of the weighing device, etc., realizing a highly versatile weight indicator can do.

  In the present specification and claims, the filter type is a characteristic function of a filter, such as a low-frequency pass type such as a first-order lag or a second-order lag, or a band frequency elimination type such as a notch filter. The filter constant is a corner frequency in the case of a first-order lag filter in a low-frequency pass filter, and a corner frequency and a damping coefficient in the case of a second-order lag and a third-order or higher-order lag. In the case of a moving average filter in the band frequency elimination filter, it is a notch frequency.

  The plurality of different filter types may include an nth-order lag (n is a positive integer) low-frequency pass filter and a notch filter that is a band-frequency elimination type.

  A moving average filter is used as the notch filter, and the filter forming means is configured to output the digital load signal when the moving average filter is selected by the filter setting means and a notch frequency is input as the filter constant. The moving average filter may be configured to determine the number of data used for calculating an average value in the moving average filter based on a sampling frequency or a sampling period and the notch frequency.

  When the filter processing means is formed by a single filter, the filter type and the filter constant for the filter are displayed, and when the filter processing means is formed by a plurality of filters, the plurality of filters are displayed. You may further provide the display means which displays the connection mode of each filter, the filter format about each said filter, and the said filter constant.

  According to this configuration, the filter type and the filter constant for the filter forming the filter processing means are displayed, and when the filter processing means is composed of a plurality of filters, the connection mode of the plurality of filters is displayed. Therefore, the filter characteristic by the filter processing means can be easily recognized.

  The present invention has the above-described configuration, can appropriately remove various noises that differ depending on the installation location of the weighing device, the type of the weighing device, etc., and can provide a highly versatile weight indicator. There is an effect.

FIG. 1 is a block diagram illustrating an example of a schematic configuration of a weighing device including a weight indicator according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a filter setting screen displayed on the display unit. FIG. 3 is a diagram illustrating an example of a filter configuration screen displayed on the display unit. FIG. 4 is a block diagram when four notch filters (moving average filters) are set. FIG. 5 is a diagram showing the relationship between the input and output of each notch filter in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout all the drawings, and redundant description thereof is omitted. Further, the present invention is not limited to the following embodiment.

(Embodiment)
FIG. 1 is a block diagram illustrating an example of a schematic configuration of a weighing device including a weight indicator according to an embodiment of the present invention.

  This weighing device is a vehicle weighing device that measures the weight of a vehicle and the like. A weighing table 1 on which an object to be weighed M (vehicle) is placed, and a digital according to the weight of the object to be weighed M that supports the weighing table 1. A digital load detector 2 for outputting a load signal and a weight indicator 3 are provided. Note that the weight indicator 3 of the present embodiment can be used even if the weighing device is a variety of weighing devices other than the vehicle weighing device, such as a weight-type quantitative filling machine.

  The weighing platform 1 has a rectangular shape in plan view, and four digital load detectors 2 are provided in this example so as to support the four corners from below.

  The digital load detector 2 includes a load sensor 4 including a load cell that supports the weighing platform 1 from below, an amplifier 5 including an operational amplifier that amplifies an analog output signal of the load sensor 4, and an analog output signal of the amplifier 5. Are sampled at intervals of sampling periods (Δt), and converted into digital signals (digital load signals) at intervals of sampling periods (Δt).

  The weight indicator 3 includes a control unit 7, an input unit 10, and a display unit 11.

  The control unit 7 includes, for example, a microcontroller and includes a calculation unit 8 including a CPU and a memory 9 including a RAM and a ROM. The calculation unit 8 controls the operation of the weighing device including the weight indicator 3 by the CPU executing an execution program of the CPU stored in the ROM of the memory 9.

  The display unit 11 includes a display (display device) that displays a weight value or the like of an object to be weighed supplied from the control unit 7 on a screen. The input unit 10 includes a keyboard, a mouse, and the like on which a user (including an employee of a weighing device manufacturer) performs an input operation to the control unit 7. The input unit 10 may be configured with a touch panel provided integrally with the display unit 11.

  Further, the amplifier 5 and the A / D converter 6 may be provided inside the casing of the weight indicator 3 and provided in the weight indicator 3. Further, an analog filter for removing high frequency noise may be provided between the amplifier 5 and the A / D converter 6.

  The control unit 7 adds (sums) the digital load signals input from each A / D converter 6 at the sampling cycle (Δt) interval, and performs a filtering process to remove noise and the like on the added signals. Based on the filtered signal, the weight of the object M is calculated and the weight value is displayed on the display unit 11. Alternatively, the digital load signal input from each A / D converter 6 is filtered and then added (summed), and the weight of the object M is calculated based on the added signal. Good.

  The control unit 7 functions as a weight calculation unit, a filter processing unit, a filter formation unit, and the like, the input unit 10 functions as a filter setting unit, and the display unit 11 functions as a display unit.

  In the present embodiment, the digital filter for performing the above filter processing on the control unit 7 can be easily set and changed. Hereinafter, this configuration will be described in detail.

  FIG. 2 is a diagram illustrating an example of a filter setting screen displayed on the screen 11 s of the display unit 11. For example, when the user presses a menu switch provided on the keyboard of the input unit 10, a menu screen (not shown) is displayed on the display unit 11, and a “filter setting” key on the menu screen is designated with the mouse. Click to switch to the filter setting screen of FIG. In this filter setting screen, a filter setting table 20 is displayed, and a plurality of filters (digital filters) constituting a synthesis filter serving as a filter processing means can be set.

  The filter setting table 20 is provided with a column for inputting a plurality of types of filter formats that can be set and filter constants of each filter. In this filter setting table 20, “x” marks indicate places where setting is not possible, and places where nothing is set are indicated by “0”. In the case of FIG. 2, four filter constant setting fields are provided for each of the filter formats of model numbers 1, 2, and 3. For example, for the first-order lag low-pass filter (low frequency pass filter) of model number 1, four filter constants with break frequencies f1 to f4 can be set, and four types of filters can be set. For the second-order lag low-pass filter (low-frequency pass filter) of type number 2, four filter constants can be set, each having a break frequency of f1 to f4 and a damping coefficient of ζ1 to ζ4. Can be set. For a notch filter (moving average filter) that is an example of a band frequency elimination filter of type number 3, four filter constants with notch frequencies f1 to f4 can be set, and four types of filters can be set. Many types of filters can be realized by freely connecting the filters.

  In this filter setting table 20, for example, the user clicks a column for inputting a filter constant using the mouse or the like of the input unit 10 (a filter format corresponding to the clicked column is selected), a keyboard or the like. The desired filter can be set by inputting a desired numerical value (filter constant).

  In the filter setting table 20 shown in FIG. 2, a first order lag low pass filter with a corner frequency (f1) of 3 Hz and a second order with a corner frequency (f1) of 3 Hz and a damping coefficient (ζ1) of 0.8. The input state is shown when a delayed low-pass filter and two notch filters having a notch frequency (f1) of 16 Hz and a notch frequency (f2) of 9 Hz are set. For example, when 3 is set in the column of the break frequency (f2) as a first-order lag low-pass filter, it means that two filters of the same filter type and the same filter constant are connected, and the same filter type is the same. Multiple filters with filter constants can be set. When the “decision” key 22 is clicked, a filter of the filter format in which the filter constant is input is set, and the filter configuration screen shown in FIG. 3 is displayed on the display unit 11.

  In some cases, only one type of filter is set, but as shown in FIG. 3, the filters (F1 to F4) of the plurality of filters set in the filter setting table 20 are connected in cascade (cascade connection). ). When a plurality of filters are cascaded in this way, the configuration is such that the front-stage filter does not receive interference from the filter connected to the rear stage. Here, the four filters F1 to F4 may be replaced in any order instead of the order shown in FIG. Each of the four filters F <b> 1 to F <b> 4 performs a filter process (filter calculation) for each sampling period Δt that is a sampling interval of the A / D converter 6. That is, each of the filters F1 to F4 receives a digital signal for each sampling period Δt, performs a filtering process, and outputs a filtered signal.

  When the “return” key 23 is clicked on the filter configuration screen shown in FIG. 3, the screen returns to the filter setting screen shown in FIG. 2, and the filter can be set again. When the “menu” key 23 shown in the screens of FIGS. 2 and 3 is clicked, the screen is switched to the menu screen. When the “filter configuration” key on the menu screen is designated and clicked with the mouse, the filter configuration screen set at that time as shown in FIG. 3 can be displayed.

  The filter setting operation as described above is performed, for example, when the weighing device is installed. When the filter configuration shown in FIG. 3 is set, the control unit 7 adds, for example, digital load signals input from all the A / D converters 6 during normal weighing operation, The added signal is filtered by the first-order lag low-pass filter F1, the output of the first-order lag low-pass filter F1 is filtered by the second-order lag low-pass filter F2, and the output of the second-order lag low-pass filter F2 is subjected to band frequency removal. The notch filter F3, which is a type filter, performs filtering, and the output of the notch filter F3 is filtered by a notch filter F4, which is a band frequency elimination filter. And the control part 7 calculates the weight of the to-be-measured object M based on the digital load signal which performed the filter process with the notch filter F4, and displays the weight value on the display part 11. FIG.

  In the present embodiment, the memory 9 of the control unit 7 stores in advance filter operation programs corresponding to a plurality of types of filter formats that can be set on the filter setting screen shown in FIG. The set filter constant is passed as an argument to the filter operation program. For a filter in which 0 is set in one place in the filter constant, the filter calculation program is not executed, and processing is performed assuming that no filter is provided. Here, three filter types corresponding to the first-order lag low-pass filter, the second-order lag low-pass filter, and the notch filter are provided as a plurality of types of filters. A filter type may be provided.

  The filter setting method shown on the filter setting screen in FIG. 2 is an example, and the present invention is not limited to this. For example, the same format, different formats, and filter constants are the same or different, and set (temporarily set) various filters together with filter numbers (for example, numbers given in the order of setting). In order to form a desired synthesis filter, by designating a plurality of appropriate numbers from among the filter numbers set so far, a synthesis filter is formed by cascading filters of the designated filter numbers. You may do it.

  Next, the three filters having format numbers 1 to 3 will be described.

  (1) When a plurality of the first-order lag low-pass filters of model number 1 are connected, the response delay increases. However, since they have real poles, the response is not vibrational and stable. The transfer function G1 (s) of this first-order lag low-pass filter is expressed by the following equation, where the corner angular frequency is ωn (rad / sec).

G1 (s) = 1 / {1+ (1 / ωn) s}
The filter of the format number 1 is a recursive filter, which converts the transfer function G1 (s) described above into a difference equation (for example, converts the transfer function into z and further converts it into a difference equation), and newly inputs data. Each time is read, a cyclic operation is performed to obtain a filtering output.

  That is, a cyclic filtering operation program whose coefficient (ωn) is undetermined corresponding to the filter of the format number 1 is stored in the memory 9 of the control unit 7 in advance. Then, the control unit 7 converts the corner frequency fn (f1 to f4) set in the filter setting table 20 into the corner angular frequency ωn (= 2πfn) in the cyclic filtering calculation program whose coefficient (ωn) is not yet determined. Then, a desired calculation program (filter) is formed.

  (2) Although the response of the second-order lag low-pass filter of model number 2 is fast, the response is oscillatory because it has complex poles. The rise of the response signal and the amplitude attenuation degree of the vibration signal differ depending on the damping coefficient. The transfer function G2 (s) of this second-order lag low-pass filter is expressed by the following equation, where the corner angular frequency is ωn (rad / sec) and the damping coefficient is ζ (0 <ζ <1).

G2 (s) = ωn ² / (s ² + 2ζωns + ωn ² )
The filter of the format number 2 is a recursive filter, which converts the transfer function G2 (s) described above into a difference equation (for example, converts the transfer function into z and further converts it into a difference equation), and newly inputs data. Each time is read, a cyclic operation is performed to obtain a filtering output.

  That is, a cyclic filtering operation program whose coefficients (ωn, ζ) are not yet determined corresponding to the filter of the format number 2 is stored in the memory 9 of the control unit 7 in advance. Then, the control unit 7 substitutes the damping coefficients ζ (ζ1 to ζ4) set in the filter setting table 20 into the cyclic filtering calculation program in which the coefficients (ωn, ζ) are undetermined, and the break frequency fn (f1 to f1). A desired calculation program (filter) is formed by converting and substituting f4) into the corner angular frequency ωn (= 2πfn).

  (3) The notch filter (moving average filter) of model number 3 has an extremely large attenuation characteristic only for a signal having a notch frequency.

  In the case of this notch filter, the control unit 7 converts the notch frequency fn (f1 to f4) set in the filter setting table 20 into a cycle Tn = 1 / fn (sec) and the sampling cycle of the A / D converter 6. Using Δt (sec), the number of taps N (the number of data used for calculating the average value) is calculated by the following equation.

N = Tn / Δt
Further, the tap number N may be calculated by the following equation using the sampling frequency fs (Hz) of the A / D converter 6 and the notch frequency fn (Hz).

N = fs / fn
In either case, N is rounded to a whole number (rounding off, etc.). Then, the control unit 7 forms a shift register including N memory cells (delay elements) for storing data, and shifts the data stored in each memory cell each time new data is read, so that the latest data is always updated. N pieces of input data are stored, and a moving average calculation program (filter) for calculating an average value thereof is formed.

  FIG. 4 is a block diagram when four notch filters (moving average filters) are set. In FIG. 4, reference numerals 41 to 44 are notch filters, and four notch filters are cascaded. For example, the first-stage notch filter 41 includes N1 memory cells S1 (0) to S1 (N1-1), (N1-1) adders 51, and a multiplier 52. Yes. The sum of N1 data stored in the memory cells S1 (0) to S1 (N1-1) is input to the multiplier 52, and the sum is multiplied by 1 / N1, thereby obtaining an average value y (n). Is calculated and input to the notch filter 42 in the second stage. The notch filters 42 to 44 in the second to fourth stages have the same configuration only in that the number of memory cells of the shift register is different (that is, the number of taps is different).

  FIG. 5 is a diagram showing the relationship between the input and output of each notch filter in FIG. In the notch filter 41 in the first stage, the average value y (n) of the latest N1 inputs x (n) is calculated for each sampling period Δt that is the sampling interval of the A / D converter 6 described above. , It is output and input to the second notch filter 42. The second-stage notch filter 42 calculates the average value y (2n) of the latest N2 inputs y (n) for each sampling period Δt, and outputs the average value y (2n) to the third-stage notch filter 43. Is done. In the third-stage notch filter 43, the average value y (3n) of the latest N3 inputs y (2n) is calculated for each sampling period Δt, which is output and input to the fourth-stage notch filter 44. Is done. In the fourth-stage notch filter 44, the average value y (4n) of the latest N4 inputs y (3n) is calculated and output for each sampling period Δt.

  As described above, when a plurality of notch filters (moving average filters) are set, multiple moving average processing is performed. Even if notch filters are not adjacently connected, multiple moving average processing is performed in the same manner.

  In the weighing device, natural vibration noise caused by an impact when an object to be weighed is supplied to the weighing device and basic vibration noise received from the installation location (foundation) of the weighing device are superimposed on the load signal. When the weighing device is a vehicle weighing device as in this example, natural vibration noise is generated when the vehicle is placed on the weighing table 1 and receives basic vibration noise from the installation location (foundation) of the weighing table 1. .

  The filter setting example in FIG. 2 is an example in which the natural vibration noise frequency is 15 to 17 Hz, for example, and the fundamental vibration noise frequency is 9 Hz, for example.

  In order to form a low-pass filter having a break frequency of 3 Hz and a gain attenuation factor of 60 dB / dec after the break frequency of 3 Hz, the filters of the form numbers 1 and 2 are entered in the f1 column of the form numbers 1 and 2. 3 is set. Further, since this weighing device is basically for static weighing, the damping coefficient ζ1 of the model number 2 is set to 0.8 in order to suppress the vibration as the step response even if the response characteristic is slow. Note that 3 is set in the f1, f2, and f3 fields of the model number 1, and each column of the model number 2 is not set to 0, but three filters of the model number 1 are set to be connected in cascade. Also good.

  The above-described low-pass filters of the model numbers 1 and 2 are used to remove vibration noise of various frequencies whose frequency is not fixed. In addition, for example, when the object to be weighed (vehicle) moves on the weighing platform 1, smooth characteristics against vibration noise whose amplitude is not constant such as a sine wave can be obtained. However, natural vibration noise in the vicinity of a frequency of 15 to 17 Hz with a large amplitude with a fixed period and fundamental vibration noise having a frequency close to the break frequency of the above-mentioned filter are at a break frequency of 3 Hz and in a frequency band larger than that- Even a low-pass filter having an attenuation characteristic of 60 db / dec cannot obtain sufficient attenuation.

  Thus, for natural vibration noise and basic vibration noise having an expected constant frequency, a notch filter that is a band frequency elimination filter of model number 3 is used to cover insufficient attenuation by the low-pass filter. . Here, a notch filter with a notch frequency (f1) of 16 (Hz) is set as a countermeasure for natural vibration noise, and a notch filter with a notch frequency (f2) of 9 (Hz) is set as a countermeasure for basic vibration noise. ing.

  In this embodiment, as shown in FIG. 2, one filter can be set by selecting an arbitrary format from a plurality of filter formats and arbitrarily setting a filter constant. Can be set arbitrarily. That is, depending on the characteristics of various vibration noises, for example, the natural vibration noises of various frequencies possessed by each part of the weighing unit, and those vibration vibrations that are attenuated by a transient response and whose amplitude changes Select a suitable filter type from the superordinate concept, such as countermeasures for fundamental vibration noise that continues at almost constant amplitude and frequency, so as to give a large damping effect to a specific frequency, and a frequency greater than a specific frequency The filter constant can be set from a lower concept so as to give a large attenuation rate to the band. By combining them arbitrarily, it is possible to easily and freely realize a synthesis filter having filtering characteristics (= characteristics regarding attenuation of vibration noise and response level) optimum for vibration noise of the weighing device used. Therefore, it is possible to appropriately remove various noises depending on the installation location of the weighing device, the type of weighing device (such as a vehicle weighing device or a weight-type quantitative filling machine), the size, etc. An indicator can be realized.

  Further, by displaying the filter configuration screen shown in FIG. 3 on the display unit 11, the configuration of the set synthesis filter is displayed, and the specifications of the cascade-connected filters (filter type and filter constant) are easily recognized. can do. Therefore, it is useful when checking the current filter characteristics, changing the filter constant, and changing the filter type.

  INDUSTRIAL APPLICABILITY The present invention can appropriately remove various noises that differ depending on the installation location of the weighing device, the type of the weighing device, etc., and is useful as a highly versatile weight indicator.

2 Digital load detector 3 Weight indicator 4 Load sensor 6 A / D converter 7 Control unit 10 Input unit 11 Display unit

Claims (4)

Filter processing means provided in a weighing device for weighing the object to be weighed, for filtering a digital load signal obtained by A / D converting the output signal of the load sensor used for weighing the object to be weighed. A weight indicator having weight calculation means for calculating the weight of the object to be weighed based on the filtered digital load signal,
A filter setting means for selecting one or a plurality of filter formats from a plurality of different filter formats stored in advance, and for inputting a filter constant that defines the characteristics of the filter configured in the selected filter format;
And a filter forming means for forming the filter processing means formed by cascading a plurality of filters whose filter types and filter constants are determined by the filter setting means.   2. The weight indicator according to claim 1, wherein the plurality of different filter types include an nth-order lag (n is a positive integer) low-pass frequency pass filter and a notch filter that is a band-frequency canceling filter. . A moving average filter is used as the notch filter,
The filter forming means includes
When the moving average filter is selected by the filter setting means and a notch frequency is input as the filter constant, the moving is performed based on the sampling frequency or sampling period of the digital load signal and the notch frequency. The weight indicator according to claim 2, wherein the weight indicator is configured to determine a number of data used for calculating an average value in an average filter and to form the moving average filter. 4. The display device according to claim 1, further comprising a display unit that displays a connection mode of a plurality of filters constituting the filter processing unit, a filter type and the filter constant for each of the filters. Weight indicator.

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