CN1028384C

CN1028384C - Electronic scale

Info

Publication number: CN1028384C
Application number: CN 91101230
Authority: CN
Inventors: 河本晟
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 1990-02-28
Filing date: 1991-02-28
Publication date: 1995-05-10
Anticipated expiration: 2006-02-28
Also published as: CN1054829A

Abstract

A PID controlled electronic scale comprises a weight measuring tray, a tray limiter for limiting the lowest position of the tray, a displacement detector for detecting the displacement of the tray, a PID operation circuit and an electromagnetic force conversion device.

Description

Electronic balance

The present invention relates to a kind of electronic scales, will be in this electronic scales by the weight of weighing by the power institute balance that produces by the electromagnetic force conversion equipment.

Such electronic scales mainly is made of self-equilibrating servo-drive system (selfequilibrating servomechanism), mainly comprise the check weighing pallet, the pallet displacement detector, be used to measure the displacement of check weighing pallet, the PID(proportion integration differentiation) control system and electromagnetic force conversion equipment, the active coil part of this device and check weighing pallet mechanical connection.The PID control system comprises a PID computing circuit, this circuit by to the proportional scaling signal of output instantaneous value (F) of pallet displacement detector, with the proportional integrated signal of the time integral value of this output valve (I) and with the proportional differential value of differential value (D) of this output valve output pid control signal that calculates and sue for peace.Except that above basic structure, also has a pallet stop when scale is put weight, be used for the displacement of check weighing pallet mechanically is limited in the interval of qualification, if this stop not, because the retarded elasticity that deformation produced of scale is answered, the big displacement meeting of check weighing pallet makes scale produce wrong measurement result.

But, the restriction of the scope of activities of check weighing pallet is caused such shortcoming, when the weighing weight, need the long period, scale just can enter equilibrium state.When the displacement of check weighing pallet is subjected to the restriction of pallet stop, no matter be placed on weight on the check weighing pallet have much, the value that the output of pallet displacement detector all keeps the pallet stop to be limited.Correspondingly, because it is desired little concerning the electromagnetic force conversion equipment that the input signal of PID computing circuit computing moves freely when catering to the weight that is placed on the pallet than check weighing pallet, just need the long time to produce power that compensation be placed on the heavier weight on the pallet and eliminate this shortcoming and can use following method in principle: have only the gain of increase PID computing circuit when the check weighing pallet continues to be on the pallet stop.But, the companion's and the shortcoming of coming is that scale causes vibration and irregular swing through regular meeting.

The object of the invention is to eliminate the above-mentioned shortcoming of the conditional electronic scale that has the pallet stop.And provide a kind of eliminate owing to the shortcoming that imposing restrictions on of the scope of activities of check weighing pallet produced through improved electronic scales.

Another object of the present invention is a kind of so improved electronic scales of structure, and it does not need to increase the gain of PID computing circuit of the inside of scale.

In order to achieve the above object, electronic scales of the present invention is except that also comprising PID computing circuit and pallet stop, also comprise and be used to detect the device whether the check weighing pallet keeps in touch with the pallet stop, and such device, have only when check weighing pallet and pallet stop keep in touch, to be used for increasing integral item coefficient at least and to multiply each other with the integral that mathematical operation comprised by above-mentioned PID circuit execution.

According to the present invention, even the weight of a weight makes the check weighing pallet be depressed into stop, measuring process also can be carried out reposefully and need not to increase the reaction time, and also can not produce additional swing in equilibrium process.

The present invention is described in more detail below with reference to accompanying drawings.

Fig. 1 has shown the block scheme of one embodiment of the invention structure;

Fig. 2 has shown the block scheme of another embodiment of the present invention structure;

Fig. 3 has shown the part process flow diagram of the major function of embodiment among depiction 1 Fig. 2;

Fig. 4 has shown the equilibrium process of the embodiment of the invention; And

Fig. 5 has shown the measurement process with the electronic scales that is not to resemble the PID control system that designs the present invention.

Referring to Fig. 1, Fig. 1 is with the basic structure of block diagram depicting one embodiment of the present of invention, its known structure of electromagnetic force conversion equipment 1(only with movable action line of force circle 13 symbols express) have a movable action line of force circles 13 that link to each other with check weighing pallet 11 machinery, and provide PID Control current through current amplifiers 5 to it by PID computing circuit 4, the displacement of check weighing pallet 11 is detected by pallet displacement detector 2, and is limited to a zone that limits by pallet stop 12.The output signal of pallet displacement detector 2 is amplified by amplifier 3, delivers to PID computing circuit 4 and level comparator 6 then simultaneously, and by it, the signal of reflection pallet displacement compares with the standard signal that the standard signal source that is arranged on level comparator 6 inside provides.The output of level comparator 6 is input to the PID computing circuit 4 later modes of stating of chatting face to face and adjusts its computing.The PID Control current that offers acting force coil 13 is transformed into correspondent voltage on output resistance 7.This voltage transfers to A/D converter 9 through wave filter 8 and carries out digitizing so that demonstrate weight measurement at numeric display unit 10.In such basic structure, when check weighing pallet 11 is forced into possible extreme lower position by pallet stop 12 restriction, be arranged on the value that is lower than the output voltage of prime amplifier 3 slightly of standard signal source output in the level comparator.So if check weighing pallet 11 is forced into above-mentioned extreme lower position, signal of level comparator 6 outputs is added on PID computing circuit 4.This signal acts on PID computing circuit 4 and increases integral item coefficient, multiplies each other with the integral that is included in the mathematical operation of being carried out by PID computing circuit 4.

Utilize the embodiment of said structure, if be placed in the interval of pallet stop 12 restrictions of the very light displacement that can guarantee pallet 11 of weight on the pallet 11, because the output voltage of prime amplifier 3 forces down 4 normal operations of PID computing circuit than the standard electric that the standard signal source that is arranged in the level comparator 6 provides.Ratio, integration and differential term are taken advantage of by its predetermined fixed coefficient separately.

On the contrary, when the check weighing pallet is put into weight, when being depressed into the extreme lower position that is limited by pallet stop 12, PID computing circuit 4 makes the increase that gathers way of the PID Control current of the acting force coil 13 that offers electromagnetic force conversion equipment 1 with the integral item coefficient computing of foregoing increase.So, when check weighing pallet 11 remains on confined extreme lower position, gravity is compensated rapidly, make check weighing pallet 11 hightail pallet stop 12, in case pallet leaves this position, the PID computing circuit with original (not increasing) integral item coefficient computing, is controlled scale reposefully and is tending towards final equilibrium state once more.This equilibrium process of representing with synthetic PID curve of output is described in Fig. 4 qualitatively.Compare with Fig. 4, Fig. 5 shown when PID computing circuit 4 be not that device becomes so that the PID curve of output of the expection of integral item coefficient can adjust the time.From the comparison of Fig. 4 and Fig. 5, can clearly find out bigger improvement has been arranged according to the response speed of electronic scales of the present invention.

In this embodiment, integral item coefficient is changed by the signal from level comparator 6, this embodiment also can correct, so that make this coefficient by having a mind to the software of design or come change with the activation signal that forms contact-making switch according to utilizing with spline structure from pallet stop 12.

Illustrated as square frame in Fig. 2, the present invention also may be used on using in the electronic scales of digitizing PID computing circuit.In Fig. 2, adopt the reference number identical with Fig. 1 with the identical structure that shows among Fig. 1.According to this embodiment, the acting force coil 13 of electromagnetic force conversion equipment 1 is carried out pulse current, pulse current obtains by the DC current of switchgear 26 continuous cutting-offs from DC current source 27, and the duty factor of this pulse current is determined the power of contending with that electromagnetic force conversion equipment 1 produces.According to the present invention, the pallet displacement that is detected by pallet detector 2 is converted to the digital displacement data by mould/number conversion circuit 21, and PID computing circuit 23 output pid control signals are advanced in input then.Pulse duty (duty) testing circuit 24 is microcomputerization (25) together with PID computing circuit 23.After receiving pid control signal, export a series of switching signal and make switchgear 26 work make the effective breadth of acting force coil 13 pulse currents that offer the electromagnetic force conversion equipment corresponding with the pid control signal of PID computing circuit 23 outputs.

Electronic scales to basic structure with as above brief introduction, if the displacement data of A/D converter 21 outputs, shift value when being forced into the extreme lower position state that limits by the pallet device corresponding to check weighing pallet 11, the software that PID computing circuit 23 usefulness have a mind to design carries out computing to the integral item coefficient that increases, so obtain the improved balanced reaction performance similar to previous embodiment shown in Figure 1.The adjustment implementation of integral item coefficient is shown in Figure 3 with the part process flow diagram equally.

This embodiment also can make amendment, so that integral item coefficient changes according to the control signal of utilizing identical structure to obtain to form a contact-making switch from pallet stop 11.

Although in the above-described embodiments, pid control signal obtains adjusting by increasing integral item coefficient, the present invention is certainly in fact by making

PID computing circuit

4 and 23 coefficients of increase with other carry out computing, as proportional and differential term coefficient, multiply each other with ratio and differential term in the mathematical operation of carrying out by the PID computing circuit.

In addition, the present invention can combine enforcement with traditional nonlinear control method, and in the method, the gain of the control system of electronic scales is to change according to the non-linear displacement ground of check weighing pallet.

Claims

1, a kind of electronic scales, has a PID control circuit (4,23), be used for displacement signal according to the displacement of representing check weighing pallet (11) and be controlled at electromagnetic balance power on the check weighing dish, it is characterized in that comprising that is limited in the load stop (12) of the downward motion of pallet 11 down, and be used for pallet be in by stop determine limit the position time set up the device (6) of increment of the integral item coefficient of a PID control circuit.

2, the electronic scales of claim 1, it is characterized in that, also comprise a switch (26), determine circuit (24) control by duty factor according to the output of PID circuit (23), be used to change a constant DC source (27), provide pulse current to balancing coil (13).

3, claim 1 or 2 electronic scales, the device that it is characterized in that being used to increasing integral coefficient is a comparator circuit (6), this circuit is with displacement signal and a predetermined reference signal relatively.

4, claim 1 or 2 electronic scales is characterized in that being used to increase the predetermined level of the device of integral coefficient in response to displacement signal.