JPH0765927B2 - Weight measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a weight measuring device effective for use in a checker, a combination weighing device, or the like that requires high-speed weighing.
In particular, the present invention relates to a weight measuring device having a signal processing circuit in which a noise component included in an output signal of a weight detector is attenuated by a filter or the like.

(Prior Art) As is well known, noise included in a detection signal of a weight detection device includes noise caused by natural vibration of a weight detection system such as a load cell and noise caused by external vibration such as floor vibration. Some are caused by vibrations generated by the main body and the octuator. Then, with respect to these vibration noises, a plurality of stages of low-pass filters are inserted and connected to the analog signal processing circuit to remove the attenuation.

FIG. 2 is a schematic block diagram of a weight measuring device used in such a checker or combination weighing device. In the figure, 1 is a weight detector including a load cell, 2 is an amplifier connected to the output stage of the weight detector 1, 3 is a filter circuit in which a plurality of low-pass filters are connected, and 4 is an output stage of the filter circuit. A level shift circuit, 5 is an A / D converter, and 6 is a microcomputer, which is connected and sets the initial load output of the weight detector 1 in the unloaded state to almost zero level. A noise component due to vibration included in the detection signal obtained by the weight detector 1 is attenuated by the filter circuit 3 and a predetermined process is performed by the microcomputer 6.

FIG. 3 is a specific example of the filter circuit 3. The filter circuit is composed of a plurality of stages, for example, three stages of low-pass filters a, b, c, and each low-pass filter is, for example, the low-pass filter a is an operational amplifier OPa, capacitors Ca ₁ , Ca ₂ , and resistors.
It is composed of Ra ₁ and Ra ₂ . The other low-pass filters b and c are also constituent elements, and the connection relation of each constituent element is the low-pass filter a.
Is similar to.

(Problems to be Solved by the Invention) Since the natural frequency of such a weight detection system greatly varies depending on the weight of the load, vibration noise is attenuated and removed by a filter circuit in which a plurality of low-pass filters are connected. In this case, the cut-off frequency of the filter circuit must be set to a considerably low safety factor in consideration of the safety factor, resulting in a slow response and a decrease in weighing speed. The present invention aims to solve the problems of the prior art,
Provided is a weight measuring device capable of effectively attenuating and removing a noise component included in a weight signal with a simple circuit configuration while improving a weighing speed.

(Means for Solving Problems) The weight measuring device of the present invention is configured as follows. That is, in a weight measuring device configured to input a noise component contained in a weight signal into a filter to attenuate the filter, the filter is cut off at a plurality of vibration frequencies generated by a weight detection system of the weight measuring device. And a plurality of notch filters having different cutoff frequencies connected in cascade and at least one or more low-pass filters connected in cascade to the notch filter.

(Operation) The present invention provides a filter circuit used in a weight measurement circuit,
The natural vibration of the weight detection system in a wide band by matching the respective cutoff frequencies with the plurality of vibration frequencies generated by the weight detection system of the weight measuring device, and by cascade-connected plural notch filters having different cutoff frequencies. The noise caused by floor vibration is removed by the low-pass filter connected in series with the notch filter, so the weight measuring device can be operated at high speed and effectively without increasing the number of low-pass filter connection stages. Can be made.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. The present invention is
In the block diagram of FIG. 2, the filter circuit 3 is configured as shown in FIG. That is, the two-stage notch filters a and b and the two-stage low-pass filters a and b form a filter circuit. Notch filter a, the capacitor C ₁ ~
The notch filter b is composed of C ₄ , resistors R _{1 to} R ₄ , and operational amplifier OP ₁ , and capacitors C _{5 to} C ₈ and resistors R ₅ to
It consists of R ₈ and operational amplifier OP ₂ . Similarly to the example of FIG. 3, the low-pass filter a is an operational amplifier OP ₃ , capacitors C ₉ and C ₁₀ , resistors R ₉ and R ₁₀ , and the low-pass filter b is an operational amplifier OP ₄ and capacitors C ₁₁ and C _12. , Resistors R ₁₁ and R ₁₂ .

Next, the operation of such a filter circuit will be explained. For the notch filters a and b, the circuit constants are selected so that the transmission zero point, that is, the cutoff frequency, is appropriately selected, and the weight detection system that changes according to the weight of the loaded item. The bandwidth is wide enough to cope with the frequency change of the natural vibration of. For example, by selecting the circuit constants so that the notch filter a has a cutoff frequency of 20 Hz and the notch filter b has a cutoff frequency of 30 Hz, noise components in a wide band of about 15 Hz to 35 Hz can be attenuated.

In addition, noise caused by external vibration such as floor vibration or vibration generated by the actuator of the main body of the equipment is low-pass filter.
It is attenuated by a and b. In this case, the noise caused by the natural vibration of the weight detection system is sufficiently attenuated by the notch filters a and b, so the number of stages of the low-pass filter can be reduced and the cut-off frequency of each stage of the low-pass filter should be increased. Therefore, the response of the entire filter circuit to the input can be accelerated.

(Effects of the Invention) As described above, according to the present invention, a filter circuit is configured by a plurality of notch filters and low-pass filters, and the noise component due to the natural frequency of the weight detection system is
By cascading a plurality of notch filters with different cutoff frequencies that match the respective cutoff frequencies with the multiple vibration frequencies generated by the weight detection system,
Attenuates and removes over a wide bandwidth. Further, since the low-pass filter only removes vibration noise such as floor vibration, the number of connection stages can be reduced. That is, by constructing the filter circuit by combining the notch filter and the low-pass filter, noise included in the detection signal of the weight detection device can be effectively removed, and high-speed processing with a quick response becomes possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a filter circuit of the present invention, FIG. 2 is a schematic block diagram of a weight measuring apparatus to which the present invention is applied, and FIG.
The figure is a circuit diagram of a conventional filter circuit. 1 ... weight detector, 2 ... amplifier, 3 ... filter circuit, 4 ... level shift circuit, 5 ... A / D converter, 6 ...
… Microcomputer.

Claims (1)

[Claims] 1. A weight measuring device in which a noise component contained in a weight signal is input to and attenuated by a filter, wherein the filter is set to a plurality of vibration frequencies generated by a weight detection system of the weight measuring device. A weight measuring device comprising a plurality of notch filters having different cutoff frequencies connected in cascade and having the same cutoff frequency, and at least one low-pass filter connected in cascade to the notch filters. .