JPH0743274B2 - Load measuring device - Google Patents

Description

The present invention relates to a load measuring device, and can be used for measuring a load such as weight.

[Background technology]

Conventionally, a load measuring device is equipped with a load detecting section having a load sensor such as a strain gauge and a DC amplifier for the load detecting section, and a weak output of the load sensor is amplified to perform a highly accurate load measurement. There are things that made it possible.

On the other hand, the zero-point output value of the load sensor shifts due to changes in the measurement environment such as temperature changes, the output value of the DC amplifier drifts, and the output of the weight sensor is disturbed by external vibration, which causes an error. . In order to reduce the influence of these environmental changes and external vibration to reduce the error, a temperature compensating circuit is provided for the load sensor and DC amplifier of the load measuring device to prevent the whole measuring system including the load measuring device. I was taking measures against shaking.

[Problems to be Solved by the Invention]

However, the temperature compensation circuit cannot sufficiently cope with changes in the measurement environment, and in some cases, manual zero adjustment of the load measuring device is required. For this reason, there has been a demand for fully automatic and reliable zero-point adjustment that eliminates measurement errors due to changes in the measurement environment.

By the way, in order to improve the accuracy of load measurement, the present applicant provides a load receiving surface at the upper ends of a pair of leaf springs while supporting a rod provided at the lower ends with a support having a notch, and We propose a load detection unit (Japanese Patent Application No. 63-168762) that enables highly accurate load measurement by measuring the displacement at the notch with a strain gauge.

Although such a load detection unit enables a sufficiently high precision measurement as compared with the conventional load detection unit, it has not always been able to sufficiently cope with the shift of the output value due to the environmental change.

An object of the present invention is to provide a load measuring device that can perform zero adjustment completely automatically and reliably.

[Means for Solving the Problems]

The load measuring device of the present invention comprises a mounting surface on which an object to be measured is mounted and a support base having an opening opened in the mounting surface, and a load receiving surface for receiving the load of the object to be measured in the upper part. A load detecting portion for detecting a load received by the load receiving surface, a load position at which the load receiving surface of the load detecting portion projects from the opening of the support base, and the load receiving surface in the opening. Support means for supporting the load detecting portion so that the load detecting portion can be moved up and down across two positions, ie, the no-load position for immersing, drive means for moving the load detecting portion up and down, and the load detecting portion while controlling the drive means. Storage means for storing data obtained by the above, and stores the no-load measurement data in a state in which the load is not applied to the load detection part by lowering the load detection part to the no-load position. On the other hand, the load detection unit Calculation for raising the load measurement position to the load position and storing the load measurement data in the state where the load is applied to the load detection unit, and calculating the measured value from the data stored in the storage unit. And a control means.

[Work]

In the load measuring device of the present invention as described above, the load detecting unit having the load receiving surface protruding and retracting with respect to the opening of the mounting surface on which the measured object is mounted is provided, so that the load detecting unit is moved up and down. The load detector can be moved from one of the loaded position and the unloaded position to the other by simply doing the above, and the calculation control unit controls the driving unit to move the load detection unit. , It becomes possible to surely recognize whether the load detection unit is currently in the loaded position or the unloaded position.

Therefore, even if the object to be measured is placed on the support table, it is possible to lower the load detection unit to put it in an unloaded state, and the arithmetic control unit automatically confirms that it is in an unloaded state. Since the recognition is performed, the zero point adjustment can be performed completely automatically and surely without any trouble of the workers and the like, thereby achieving the above object.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a load measuring device 1 according to the present invention. A base 11 of the device 1 has a pair of support stands 12 and 13 provided upright at predetermined intervals. The support bases 12 and 13 have horizontal surfaces of the same height on the upper part, and this surface is a mounting surface on which the object to be measured 14 is placed.
It is said to be 15,16. An upward opening 17 is formed between the mounting surfaces 15 and 16, and the load detecting portion is formed in the opening 17.
30 is provided so as to be movable up and down.

That is, the support base 13 on the right side in the drawing has a U-shape, the pulse motor 21 is fixed to the outer surface thereof, and the drive shaft of the pulse motor 21 penetrates the side wall of the support base 13 and is fitted into the pin-on 22. There is.

In addition, between the tip of the U-shaped opening side of the support base 13,
A guide member 23 is provided upright. A slider 25 is vertically movably attached to the guide member 23 via a bearing 24 such as a rolling bearing. This slider 25 support 13
On the side, a rack that meshes with the pinion 22 of the pulse motor 21
26 is fixed.

On the other hand, an arm 27 is fixed on the side of the slider 25 opposite to the rack 26, that is, on the side of the opening 17, and the load detector 30 is supported by the slider 25 via the arm 27. The guide member 23, the slider 25, and the arm 27 constitute a support means for supporting the load detection unit 30 so as to be able to move up and down. A drive means 20 is configured to include the pulse motor 21, the pinion 22 and the rack 26, and the load detection unit 30 is vertically movable with respect to the support base 13 by the forward and reverse rotations of the pulse motor 21.

In order to set the vertical movement range of the load detection unit 30, the proximity sensors 28, 29 are provided on the side surface of the support base 12 on the left side in the drawing.
Are mounted above and below, and the power supply of the pulse motor 21 can be cut off by the operation of the sensors 28 and 29.

A weighing pan 31 is attached to the upper portion of the load detection unit 30. The upper surface of the weighing pan 31 serves as a load receiving surface 32 that receives the load of the object to be measured 14, and the load receiving surface 32 projects from the opening 17 when the load detector 30 moves up and down. It is also possible to move between two positions, a non-load position and a position to be immersed in the opening 17.

As shown in FIG. 2, the load detection unit 30 for detecting the load of the object to be measured 14 is provided with a load transmission shaft 33 protruding downward from the lower surface of the weighing pan 31. This load transmission shaft 33
Is fixed by penetrating through the central portions of parallel leaf springs 34, 35 provided below the weighing pan 31, and the load transmission shaft 33 is supported by these leaf springs 34, 35 so as to be vertically movable. Further, the lower end of the load transmission shaft 33 is in contact with a support plate 36 which is provided with a notch to facilitate displacement. A load sensor 37 is attached to the lower surface of the support base 36.
Thus, the load applied to the load receiving surface 32 of the weighing pan 31 can be detected.

In addition, a flange 38 is provided at an intermediate portion of the load transmission shaft 33. Below this flange 38,
3 with an eccentric cam 39A that regulates downward displacement of the rod
9 are arranged. Therefore, the maximum allowable displacement amount of the load transmission shaft 33 can be adjusted by rotating the rod 39 and changing the angular position of the eccentric cam 39A.

FIG. 3 shows an electrical configuration of the load detection unit 30 and includes an electric circuit 40 that amplifies the output signal of the load sensor 37.

The electric circuit 40 is a load sensor formed in a bridge circuit shape.
The output side of the sensor 37 is provided with an amplifier 42 such as an operational amplifier connected via a zero-point adjusting variable resistor 41 of the sensor 37 so that the load signal of the load sensor 37 can be amplified. Input to the output side of the amplifier 42 is a span adjustment variable resistor 43 for adjusting the voltage value of the signal, a low-pass filter 44 for passing only the low-frequency component of the load signal, and an external hold signal input. The sample and hold circuit 45 which holds the value of the load signal and outputs the held value signal is sequentially connected. The output of the sample / hold circuit 45 is the output of the load detector 30.

The output of the load detection unit 30 is connected to an arithmetic control unit 50 that controls the drive unit 20 while taking in the output as data and performing arithmetic processing.

As shown in FIG. 4, the arithmetic and control unit 50 is provided with a CPU 51 including a microprocessor and the like. This C
A bus line 52 for transmitting / receiving signals to / from other circuits and the like is connected to the PU 51. An A / D converter circuit 53 that inputs the load signal of the load detection unit 30 to the bus line 52, converts it into digital data, and loads it into the CPU 51
Is connected to the pulse motor 21 via a motor driver circuit 54, and an I / O circuit 55 that enables control of the pulse motor 21 by a command signal from the CPU 51 and a RAM 56 as storage means are connected. .

The CPU 51 is provided with an output for transmitting a hold signal to the load detection unit 30 and is also equipped with a predetermined program. By installing this program, the CPU 51 controls the pulse motor 21 to capture the output of the load detection unit 30 at the loaded position where the load of the DUT 14 is applied to the load detection unit 30 and the unloaded position where it is not applied, and these are output. The load measurement data and the no-load measurement data are stored in the RAM 56, respectively, and the no-load measurement data is subtracted from the load measurement data to calculate the measurement value.

Here, in loading the load signal of the load detection unit 30, the CPU 51 uses the output of the clock circuit 57 connected to the CPU 51 itself as a trigger signal. The clock circuit 57 outputs a signal at a cycle extremely shorter than the cycle of external vibration, for example, a cycle of 50 μs or more. As a result, the CPU 51 is capable of performing high-speed sampling hundreds to thousands of times per second in the above cycle, and performing unit data collection for collecting a data group consisting of a large number of data obtained by these samplings. Further, the unit data collection is repeated a plurality of times, and the measurement is performed by changing the sampling period in the unit data collection.

The bus line 52 is connected to an operation key 58 for setting parameters of the CPU 51 and a display 59 for displaying measured values.

Next, the operation of this embodiment will be described.

First, the object to be measured 14 is placed by straddling the placement surfaces 15 and 16 of the support bases 12 and 13 of the load measuring device 1, and the power of the load measuring device 1 is turned on, whereby the following operations are automatically performed. Is done in a regular manner. That is, with the load receiving surface 32 of the weighing pan 31 immersed in the opening 17, the CPU 51 collects unit data for the load detection unit 30 multiple times in the unloaded state, and measures the obtained data group with no load. A data group is stored in the RAM 56, these data are added to calculate an average value, and the average value is stored in the RAM 56 as a measurement value under no load.

Here, in the data collection, as shown in FIG. 5, unit data collection is performed once with a sampling cycle shorter than the cycle of external vibration, and data of both peaks and valleys of the waveform of external vibration is obtained. By calculating the average value,
The plus side error of the peak data and the minus error of the valley data are offset.

At this time, the external vibration contains a harmonic component, and with this harmonic component,
Even if there is a possibility that only the data of the peaks or valleys of the harmonics may be collected in synchronization with the sampling cycle of one of the unit data collections that are performed multiple times, the sampling cycle of other unit data collections Since a large number of pieces of data are collected for both the peaks and valleys for the harmonic components, the average value calculated from these data approaches the true value of the measurement.

Then, the pulse motor 21 is driven to open the weighing pan 31 into the opening 17
Then, the load of the DUT 14 is applied to the load detection unit 30. In this state, unit data collection of the load state is performed multiple times, and the obtained data group is stored in the RAM 56,
The average value of these data is calculated, and this average value is stored in the RAM 56 as a measured value under load.

Here, also in the unit data collection in the load state, as in the case of no load, the sampling cycle in each unit data collection is made different, the average value is calculated, and the error is offset.

Finally, subtract the measured value when there is no load from the measured value when there is a load to eliminate errors such as drift and shift that occur due to changes in the measurement environment, and display this value on the display 59 as the final measured value. To do.

According to this embodiment as described above, there are the following effects.

That is, the load receiving surface 32 of the load detection unit 30 is projected and retracted from the opening 17, the load detection unit 30 is moved to a position where the load of the DUT 14 is applied and a position where the load is not applied, and load measurement data and no-load measurement data. Since the measured value under load and the measured value under no load obtained from these data are subtracted to obtain the measured value, errors such as drifts and shifts caused by changes in the measurement environment are eliminated. The zero point adjustment to be removed can be accurately performed.

Moreover, even when the object to be measured 14 is placed on the support bases 12 and 13, the load detection unit 30 automatically descends to be in an unloaded state, and the arithmetic control unit 50 is in the unloaded position. Is automatically recognized, the zero point adjustment can be performed completely automatically and reliably without any troubles such as workers.

In addition, unit data is collected at a sampling cycle shorter than the cycle of external vibration so that data for both peaks and valleys of the waveform of external vibration is obtained. Since it is canceled by the minus side error of the data of the part, the error due to external vibration can be removed.

Furthermore, since the unit data collection was repeated multiple times and the sampling periods for these unit data collections were made different, even if the external vibration contains harmonics, both peaks and valleys of this harmonic A large number of pieces of data can be collected, and the error due to the high frequency component of external vibration can be removed by calculating the average value of these data.

The present invention is not limited to the above-described embodiments, and modifications, improvements, etc. within the range in which the object of the present invention can be achieved are included in the present invention.

For example, in the above-described embodiment, the support bases 12 and 13 are fixed to the base 11, and the load detection unit 30 is movably provided. Conversely, the load detection unit 30 is fixed to the base 11, and the support bases 12 and 13 are fixed. 13 may be provided so as to be movable.

Further, the unit data collection may be performed only once, or in the unit data collection only once, the data collection may be performed while changing the sampling interval within a range shorter than the cycle of the external vibration. Further, the random number generation function of the CPU may be used to change the sampling interval. At this time, the random number generation function of the CPU sequentially generates random numbers,
Each time a random number is generated, the sampling interval may be changed based on the random number.

Furthermore, when measuring a fluid such as a liquid, weigh a container such as a cup that contains the fluid in advance and set it so that the measured value of this container is added to the measured value when there is no load. The fluid load may be measured later.

Further, in the above embodiment, the driving means 20 is the pulse motor 21,
Although it is composed of the pin-on 22 and the rack 26, etc., it is not limited to this, and it may be composed of a motor-driven ball screw or a cylinder device which can be expanded or contracted by hydraulic pressure or pneumatic pressure. do it.

Furthermore, in the above-described embodiment, the no-load measurement data is collected first, but conversely, the load measurement data may be collected first.

〔The invention's effect〕

As described above, according to the load measuring device and the load measuring method of the present invention, it is possible to obtain the effect that the zero point adjustment for eliminating the measurement error due to the change of the measurement environment can be performed completely automatically and surely.

[Brief description of drawings]

FIG. 1 is a side view showing an essential part of an embodiment of the present invention, FIG. 2 is a partially cutaway side view showing an essential part of a load detecting part of the embodiment, and FIG. 3 is a load of the embodiment. FIG. 4 is a schematic circuit diagram showing the circuit configuration of the detection unit, FIG. 4 is a block diagram showing the schematic configuration of the arithmetic control means of the above-mentioned embodiment, and FIG. 5 is a graph explaining the operation of the above-mentioned embodiment. 1 ... Load measuring device, 12, 13 ... Supporting base, 14 ... Object to be measured, 15, 16 ... Mounting surface, 17 ... Opening part, 20 ... Driving means, 23 ... Supporting means A guide member, 25 ... a slider constituting a supporting means, 27 ... an arm constituting a supporting means, 30 ... a load detecting portion, 32 ... a load receiving surface, 50 ... an arithmetic control means, 56 ... a storage means As RAM.

Claims (1)

[Claims] 1. A support base having a mounting surface on which an object to be measured is mounted and an opening opened in the mounting surface, and a load receiving surface for receiving a load of the object to be measured, A load detecting portion for detecting a load received by the load receiving surface, a loaded position where the load receiving surface of the load detecting portion projects from the opening of the support base, and a position where the load receiving surface sinks into the opening. Support means for supporting the load detecting portion so as to be able to move up and down across two positions of the load position, drive means for moving the load detecting portion up and down, and controlling the drive means and being obtained by the load detecting portion. While having storage means for storing data, the load detecting section is lowered to the no-load position and the load detecting section stores the no-load measurement data in a state in which the load is not applied to the storage section. The load detector is loaded with the load. Arithmetic control means for storing the load measurement data in a state in which the load is raised to a position and the load is applied to the load detection portion, and for calculating a measurement value from the data stored in the storage means. A load measuring device comprising: