Scale with overload detection measured by auxiliary voltage

Abstract

A device and method for detection of an overload on a scale which operates by the principle of electromagnetic force compensation The device and method employing, in addition to the measurement voltage arising across a measurement resistor of the scale, an auxiliary voltage that is different from the measurement voltage. The auxiliary voltage being tapped at the input to the compensation coil of the scale or at the output of the compensation coil.

Claims

1. A scale which operates by the principle of electromagnetic force compensation, the scale including: (a) a magnet; (b) a compensation coil movable relative to the magnet; (c) an output stage having an output connected to the compensation coil to supply an electrical current to the compensation coil to maintain the position of the compensation coil relative to the magnet; (d) a measurement resistor connected in series with the compensation coil between the compensation coil and a reference voltage; (e) an auxiliary measurement voltage node located between the output of the output stage and the compensation coil or between the compensation coil and the measurement resistor to provide an auxiliary measurement voltage; and wherein a measurement resistor voltage across the measurement resistor is representative of a weight measurement value for the scale when a load force within a first load force range is introduced onto a load receiving element of the scale, and the auxiliary measurement voltage indicates an overload case when a load force outside the first load force range is introduced onto the load receiving element of the scale.

2. The scale of claim 1: (a) further including a first A/D converter and a signal switching arrangement operable to switch between a first input of the first A/D converter and a second input of the first A/D converter; (b) wherein the first input of the first A/D converter is coupled to the measurement resistor voltage; and (c) wherein the second input of the first A/D converter is coupled to the auxiliary measurement voltage.

3. The scale of claim 2 wherein the measurement resistor voltage receives a first amplification before the first input of the first A/D converter and the auxiliary measurement voltage receives a second amplification before the second input of the first A/D converter, the second amplification being less than the first amplification.

4. The scale of claim 2 wherein the first A/D converter provides a first measurement range for a signal received at the first input of the first A/D converter and provides a second measurement range for a signal received at the second input of the first A/D converter, the first measurement range being different from the second measurement range.

5. The scale of claim 1: (a) further including a first A/D converter and a second A/D converter; (b) wherein an input of the first A/D converter is coupled to the measurement resistor voltage; and (c) wherein an input of the second A/D converter is coupled to the auxiliary measurement voltage.

6. The scale of claim 5 wherein the measurement resistor voltage receives a first amplification before the input of the first A/D converter and the auxiliary measurement voltage receives a second amplification before the input of the second A/D converter, the second amplification being less than the first amplification.

7. The scale of claim 5 wherein the first A/D converter provides a first measurement range for a signal received at the input of the first A/D converter and the second A/D converter provides a second measurement range for a signal received at the input of the second A/D converter, the first measurement range being different from the second measurement range.

8. The scale of claim 1 further including a control unit operable to output an overload signal when one of the auxiliary measurement voltage and a signal generated from the auxiliary measurement voltage exceeds a presettable limit value.

9. The scale of claim 1 further including mechanical overload safety means and a control unit, wherein the control unit is operable to generate a signal corresponding to an actuating force of the mechanical overload safety means or a value derived therefrom by evaluating one of the auxiliary measurement voltage and a signal generated from the auxiliary measurement voltage.

10. The scale of claim 1 further including mechanical overload safety means and a control unit, wherein the control unit is also operable to detect an actuation of the mechanical overload safety means by comparison of one of the auxiliary measurement voltage and a signal generated from the auxiliary measurement voltage with one or more presettable threshold values or by analysis of a timewise course of one of the auxiliary measurement voltage and the signal generated from the auxiliary measurement voltage.

11. The scale of claim 1 further including a control unit operable for storing in memory (i) values for the measurement resistor voltage or a respective signal generated therefrom over time and (ii) values for the auxiliary measurement voltage or a respective signal generated therefrom over time.

12. The scale of claim 1 further including a control unit operable for detecting, evaluating, or outputting a time point or a number, kind, magnitude, and duration of instances of exceeding a presettable voltage limit value for the measurement resistor voltage or a respective signal generated therefrom or of instances of exceeding a presettable voltage limit value for the auxiliary measurement voltage or a respective signal generated therefrom.

13. A method for a scale which operates by the principle of electromagnetic force compensation and including a magnet, a compensation coil movable relative to the magnet, and an output stage having an output connected to the compensation coil to supply an electrical current to the compensation coil to maintain the position of the compensation coil relative to the magnet, the method including: (a) measuring a measurement resistor voltage across a measurement resistor connected between the compensation coil and a reference voltage, the measurement resistor voltage being representative of a weight measurement value for the scale when a load force within a first load force range is introduced onto a load receiving element of the scale; and (b) at least when the measurement resistor voltage or a signal generated therefrom exceeds a presettable voltage limit value therefor, measuring and evaluating an auxiliary measurement voltage tapped between the output of the output stage and the compensation coil or between the compensation coil and the measurement resistor, the auxiliary measurement voltage or a signal generated therefrom indicating an overload case when a load force outside the first load force range is introduced onto the load receiving element of the scale.

14. The method of claim 13 further including outputting an overload signal when the auxiliary measurement voltage or the signal generated therefrom exceeds one or more presettable limit values therefor.

15. The method of claim 13 further including outputting, or displaying, or storing the auxiliary measurement voltage or a value corresponding to the auxiliary measurement voltage, or a time point, a number, a kind, a magnitude, or a duration of instances in which the measurement resistor voltage or the signal generated therefrom exceeds the presettable voltage limit value therefor.

16. The method of claim 13 further including interrupting scale operation or preventing the output of a weight value for a presettable duration when the auxiliary measurement voltage or the signal generated therefrom exceeds a presettable voltage limit value therefor.

17. The method of claim 13 including zeroing or adjusting the scale in response to the auxiliary measurement voltage or the signal generated therefrom exceeding a presettable voltage limit value therefor.

18. A method for testing an overload safety device in a scale which operates by the principle of electromagnetic force compensation and including (i) a magnet, (ii) a compensation coil movable relative to the magnet, (iii) an output stage having an output connected to the compensation coil to supply an electrical current to the compensation coil to maintain the position of the compensation coil relative to the magnet when a load force within a first load force range is introduced onto a load receiving element of the scale, (iv) a measurement resistor connected in series with the compensation coil between the compensation coil and a reference voltage, and (v) a measurement resistor voltage output providing an output of a voltage across the measurement resistor, the method including: (a) evaluating an auxiliary measurement voltage tapped between the output of the output stage and the compensation coil or between the compensation coil and the measurement resistor to determine a value corresponding to an actuating force of the overload safety device; and (b) comparing the auxiliary measurement voltage or a signal generated therefrom to one or more presettable limit values in order to identify an occurrence of an actuation of the overload safety device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first embodiment of a scale according to the invention with two separate A/D converters.

(2) FIG. 2 shows an alternative embodiment for processing the measurement resistor voltage U.sub.R and auxiliary voltage U.sub.H with just one A/D converter.

(3) FIG. 3 shows another embodiment of a scale according to the invention with two separate A/D converters and auxiliary measurement voltage.

DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

(4) FIG. 1 is a schematic representation showing the simplified circuitry of a scale according to the invention in a first embodiment. An output stage E is designed to output a coil current I.sub.L, which flows through a compensation coil L and a measurement resistor R connected in series with it. The coil L interacts with a magnet M and is disposed at the end of a lever arm K, which receives a force F introduced to the lever. By controlling the coil current I.sub.L, a counterforce is generated on the coil L, which holds the lever arm nearly motionless in its set position. If force F is greater, a higher coil current I.sub.L is needed to generate the counterforce, while a lower force F requires a correspondingly lower coil current I.sub.L (the coil current can be unipolar or bipolar).

(5) To measure the force F, the voltage U.sub.R produced across the measurement resistor R by coil current I.sub.L is tapped, amplified, and/or processed in an amplifier/filter V.sub.1 and sent to a first A/D converter AD.sub.1, which has a measurement range M.sub.1. The A/D converter AD.sub.1 outputs a digital value corresponding to the measurement resistor voltage U.sub.R to a control unit C as long as the measurement resistor voltage U.sub.R moves within the measurement range M.sub.1. Since the measurement resistor voltage U.sub.R is a measurement of the force F, said force can be determined by evaluating the data sent to the control unit C.

(6) At output A of the output stage E is an output stage voltage U.sub.E, which in this embodiment corresponds to the auxiliary voltage U.sub.H registered according to the invention. The auxiliary voltage U.sub.H is again amplified and/or processed by an amplifier/filter V.sub.2 and sent to a second A/D converter AD.sub.2, whose measurement range M.sub.2 is correspondingly greater than the measurement range M.sub.1 of the first A/D converter AD.sub.1 or joins it, so that a voltage lying outside the measurement range M.sub.1 of the first A/D converter AD.sub.1 lies within the measurement range M.sub.2 of the second A/D converter AD.sub.2. The signals output by the second A/D converter AD.sub.2 are also sent to the control unit C for evaluation.

(7) As long as the measurement resistor voltage U.sub.R moves within the measurement range M.sub.1, a weight value corresponding to the force F can be determined in the control unit C from the signals provided by the A/D converter AD.sub.1. If, on the other hand, the force F increases so much that the measurement resistor voltage U.sub.R lies outside the measurement range M.sub.1, the force F can no longer be quantified with the A/D converter AD.sub.1. However, the auxiliary voltage U.sub.H registered in addition to the measurement resistor voltage U.sub.R, which likewise increases with increasing force F, can be registered and quantified via the second A/D converter AD.sub.2 as long as the auxiliary voltage U.sub.H lies within the measurement range M.sub.2 of the second A/D converter AD.sub.2. With increasing force F, the auxiliary measurement voltage U.sub.H will then increase further until

(8) (a) the maximum output voltage (control) of the output stage E has been reached, so that it can no longer make available sufficient coil current I.sub.L to generate a sufficient counterforce in the coil L and to hold the lever K in the set position, or

(9) (b) a mechanical overload safety means T is actuated, so that the coil current I.sub.L is set to a constant value.

(10) In both cases, overloading of the scale can already be established by the fact that the measurement resistor voltage U.sub.R leaves the measurement range of the A/D converter AD.sub.1, or exceeds a threshold found just before that, or the A/D converter outputs a corresponding signal. In case (a), the force actuating the overload safety means can be determined only qualitatively, since the output stage E has reached its compensation load and the auxiliary voltage U.sub.H is no longer associated in a defined way with the force F or exceeds the measurement range M.sub.2. In case (b), however, the fact that the overload safety means T has been actuated can be established from the timewise course of the auxiliary measurement voltage U.sub.H and the resulting maximum value of said voltage, and the actuating force can be determined quantitatively, since the auxiliary measurement voltage U.sub.H still lies within the measurement range M.sub.2.

(11) FIG. 2 shows a solution according to the invention that has been modified with respect to FIG. 11, where the first A/D converter AD.sub.1 is optionally used to register the measurement resistor voltage U.sub.R or the auxiliary voltage U.sub.H. If the measurement resistor voltage U.sub.R sent to the A/D converter AD.sub.1 exceeds the measurement range M.sub.1 or a definable threshold just before that, the A/D converter AD.sub.1 is switched (or it switches itself) in order to register the auxiliary voltage U.sub.H instead of the measurement resistor voltage U.sub.R.

(12) With the switching of the signal source at the input of the A/D converter AD.sub.1, the measurement range of the converter can also be switched (preferably internally by the converter itself). For example, the sensitivity of the converter can be halved and thus the measurement range doubled. Alternatively, the amplification V.sub.2 of the auxiliary measurement voltage could be reduced enough that the higher auxiliary measurement voltage also lies within the measurement range M.sub.1.

(13) The switch W causing the switching between the two voltages can be disposed outside or even on an A/D converter circuit board, so that its control can take place directly via the control of the A/D converter or, for example, even by the control unit C.

(14) FIG. 3 shows an embodiment of the invention that has been modified with respect to FIG. 1. Unlike FIG. 1, the auxiliary measurement voltage here is not tapped between the output stage E and the coil L, but rather between coil L and the measurement resistor R (depending on the tapping point and the line resistance, it is also possible in this case for the auxiliary measurement voltage U.sub.H to differ from the measurement resistor voltage U.sub.R). The A/D converter AD.sub.2 can, as described with respect to FIG. 1, register the auxiliary measurement voltage again in a suitably amplified quantity and/or in a suitable measurement range M.sub.2 and transmit it to the control unit for evaluation.

(15) As used herein, whether in the above description or the following claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, that is, to mean including but not limited to. Also, it should be understood that the terms “about,” “substantially,” and like terms used herein when referring to a dimension or characteristic of a component indicate that the described dimension/characteristic is not a strict boundary or parameter and does not exclude variations therefrom that are functionally similar. At a minimum, such references that include a numerical parameter would include variations that, using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.), would not vary the least significant digit.

(16) Any use of ordinal terms such as “first,” “second,” “third,” etc., in the following claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another, or the temporal order in which acts of a method are performed. Rather, unless specifically stated otherwise, such ordinal terms are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term).

(17) The term “each” may be used in the following claims for convenience in describing characteristics or features of multiple elements, and any such use of the term “each” is in the inclusive sense unless specifically stated otherwise. For example, if a claim defines two or more elements as “each” having a characteristic or feature, the use of the term “each” is not intended to exclude from the claim scope a situation having a third one of the elements which does not have the defined characteristic or feature.

(18) The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit the scope of the invention. Various other embodiments and modifications to these preferred embodiments may be made by those skilled in the art without departing from the scope of the present invention. For example, in some instances, one or more features disclosed in connection with one embodiment can be used alone or in combination with one or more features of one or more other embodiments. More generally, the various features described herein may be used in any working combination.