Scale with overload detection

Abstract

The disclosure relates to a scale operating according to the principle of electrodynamic force compensation and to a method for its operation. An automatic switchover from a measuring mode to an overload mode is provided for detecting overload forces. In this overload mode the load resistance formed by a coil and at least one measuring resistor is reduced in order to allow a higher coil current at the same output stage power.

Claims

1-12. (canceled)

13. A scale which operates according to the principle of electrodynamic force compensation, the scale including: (a) a carrying coil and a magnet which interact with one another and are movable relative to one another, wherein the carrying coil is connected in a load coil circuit to receive a carrying coil current supplied to the carrying coil from an output stage; (b) a resistor arrangement which forms an electrical load resistance for the load coil circuit, the resistor arrangement comprising the load coil having a coil electrical resistance and a measuring resistor arrangement having a measuring electrical resistance, wherein the scale operates in a measuring mode for a force acting on the scale in a predetermined load measuring range, the electrical load resistance having a measuring mode resistance value when the scale is operating in the measuring mode so that the carrying coil current supplied to the carrying coil by the output stage comprises a carrying coil measuring current to compensate, by electrodynamic interaction between the carrying coil and the magnet, for the force acting on the scale and the scale determines a measured value associated with the force acting on the scale from a measuring voltage drop at the measuring resistor arrangement; and (c) a switching arrangement for switching from the measuring mode to an overload mode for detecting an overload force acting on the scale which exceeds or falls below the predetermined load measuring range, wherein in the overload mode the electrical load resistance is reduced from the measuring mode resistance value and wherein the carrying coil current supplied to the carrying coil by the output stage comprises a carrying coil overload current to compensate, by electrodynamic interaction between the carrying coil and the magnet, for the overload force acting on the scale.

14. The scale of claim 13 wherein when the scale is operating in the overload mode the carrying coil overload current is quantitatively determined by tapping an overload detection voltage within the load coil circuit and feeding the overload detection voltage to an A/D converter.

15. The scale of claim 13 further including a first A/D converter with a first load measuring range to which a voltage representing the measuring voltage drop is fed when the scale is operating in the measuring mode and wherein a transition between a force within the predetermined load measuring range and an overload force outside the predetermined load measuring range is detectable in that the voltage representing the measuring voltage drop exceeds or falls below a predeterminable threshold value for the first load measuring range of the first A/D converter.

16. The scale of claim 13 further including: (a) a first A/D converter with a first load measuring range to which a voltage representing the measuring voltage drop is fed when the scale is operating in the measuring mode; and (b) a second A/D converter with a second load measuring range to which an auxiliary voltage tapped within the load coil circuit is fed when the scale is operating in the measuring mode, wherein a transition between a force within the predetermined load measuring range and an overload force outside the predetermined load measuring range is detectable in that the auxiliary voltage exceeds or falls below a predeterminable threshold value for the second load measuring range.

17. The scale of claim 16 wherein the second load measuring range of the second A/D converter is selected to be larger than the first load measuring range of the first A/D converter.

18. The scale of claim 13 wherein the electrical load resistance is reduced in the overload mode by short circuiting a measuring resistor in the measuring resistor arrangement.

19. The scale of claim 13 wherein the electrical load resistance is reduced in the overload mode by replacing a measuring resistor in the measuring resistor arrangement with an additional resistor having an electrical resistance less than the measuring resistor.

20. The scale of claim 13 wherein the electrical load resistance is reduced in the overload mode by connecting an additional resistor in parallel with a measuring resistor of the measuring resistor arrangement.

21. The scale of claim 13 wherein the electrical resistance of the resistor arrangement is reduced by at least 50% in the overload mode.

22. The scale of claim 13 wherein the electrical resistance of the resistor arrangement is reduced by at least 80% in the overload mode.

23. The scale of claim 13 wherein the electrical resistance of the resistor arrangement is reduced by at least 90% in the overload mode.

24. The scale of claim 13 wherein the electrical resistance of the resistor arrangement is reduced by at least 95% in the overload mode.

25. The scale of claim 13 further including a first A/D converter with a first load measuring range to which a voltage representing the measuring voltage drop is fed when the scale is operating in the measuring mode and wherein: (a) the scale is operable to switch to the overload mode when a measured value exceeds a predefined first threshold value to signal an overload, in order to (i) feed a reduced measuring resistor voltage to the first A/D converter for determining the overload force, or (ii) supply an auxiliary voltage tapped at the resistor arrangement to a second A/D converter with a second load measuring range for determining the overload force; and (b) the scale is operable to switch back from the overload mode to the measuring mode when the measured value falls below the predefined first threshold value or a predefined second threshold value different from the predefined first threshold value.

26. The scale of claim 13 wherein the output stage is operable to at least double the current flowing through the resistor arrangement when the scale is operating in the overload mode as compared to the current flowing through the resistor arrangement when the scale is operating in the measurement mode.

27. The scale of claim 13 upon switching between the measuring mode and the overload mode the carrying coil current adjusts to a required compensation current within less than 500 ms from the time of switching.

28. A method for operating a scale according to the principle of electrodynamic force compensation, wherein the scale includes, (i) a carrying coil and a magnet which interact with one another and are movable relative to one another, wherein the carrying coil is connected in a load coil circuit to receive a carrying coil current supplied to the carrying coil from an output stage; and (ii) a resistor arrangement which forms an electrical load resistance for the load coil circuit, the resistor arrangement comprising the load coil having a coil electrical resistance and a measuring resistor arrangement having a measuring electrical resistance, wherein the scale operates in a measuring mode for a force acting on the scale in a predetermined load measuring range, the electrical load resistance having a measuring mode resistance value when the scale is operating in the measuring mode so that the carrying coil current supplied to the carrying coil by the output stage comprises a carrying coil measuring current to the carrying coil to compensate, by electrodynamic interaction between the carrying coil and the magnet, for the force acting on the scale and the scale determines a measured value associated with the force acting on the scale from a measuring a voltage drop at the measuring resistor arrangement, the method including: (a) detecting an overload force that exceeds or falls below the predetermined load measuring range; and (b) switching to an overload mode in which the electrical load resistance is reduced from the measuring mode resistance value to minimize relative movement between the magnet and carrying coil.

29. The method of claim 28 wherein after switching to the overload mode the output stage supplies the carrying coil with a carrying coil overload current which compensates for the overload force in order to evaluate a measured variable which is dependent on the overload coil current and determine the overload force, the measured variable comprising a voltage supplied to an A/D converter.

30. The method of claim 28 wherein the electrical load resistance is reduced by short circuiting a measuring resistor in the measuring resistor arrangement.

31. The method of claim 28 wherein the electrical load resistance is reduced by replacing a measuring resistor in the measuring resistor arrangement with an additional resistor having an electrical resistance less than the resistance of the measuring resistor.

32. The method of claim 28 wherein the electrical load resistance is reduced by connecting an additional resistor in parallel with a measuring resistor of the measuring resistor arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 shows a magnetic coil system of a prior art scale.

[0047] FIG. 2 shows a first embodiment of a circuit for reducing load resistance in accordance with aspects of the invention.

[0048] FIG. 3 shows a second embodiment of a circuit for reducing load resistance.

[0049] FIG. 4 shows a third embodiment of a circuit for reducing load resistance.

[0050] FIG. 5 shows a fourth embodiment of a circuit for reducing load resistance.

[0051] FIG. 6 shows an embodiment of a circuit for reducing load resistance within the scope of the present invention that employs a second A/D converter.

[0052] FIG. 7 shows an additional embodiment of a circuit for reducing load resistance employing a second A/D converter.

DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

[0053] FIG. 1 shows a simplified schematic representation of the measuring system of a prior art scale that operates according to the principle of electrodynamic force compensation. A force F.sub.m lying in an intended load measuring range or an overload force F.sub.u lying outside this load measuring range actsfor example via a leveron a coil L, which can move relative to a stationary magnet G. In this example, the magnet G is stationary and the coil L is coupled to the lever. In the unloaded state, coil L and magnet G are in an initial position relative to each other. A coil current I.sub.L is provided by an output stage E with the aid of an unspecified position sensor and a controller by regulating the output stage voltage U.sub.E, which current flows through the coil L and a measuring resistor W.sub.1 connected in series with the coil. The coil current I.sub.L generates a compensating force through electrodynamic interaction with the magnet G, which compensates for the deflection of the coil relative to the magnet caused by the force F.sub.m, F.sub.u and forces the coil back to its initial position.

[0054] In a measuring mode (m) representing the regular operation of the scale, forces F.sub.m are measured which are within a predetermined load measuring range. For this purpose, a measuring resistor voltage U.sub.W1 dependent on the coil current I.sub.L is tapped at the measuring resistor W.sub.1 and fed via an amplifier not specified in more detail to a first A/D converter A.sub.1 with an associated load measuring range B.sub.A1. The signals output by the first A/D converter A.sub.1 are fed to a control unit C for evaluation and output of a weight value corresponding to the force F.sub.m, F.sub.u.

[0055] The coil L with its electrical coil resistance R.sub.L and the measuring resistor W.sub.1 with its electrical measuring resistance R.sub.W1 have the coil current I.sub.L flowing through them in series and together form a resistor arrangement W, also called a load resistor, with an electrical resistance R.sub.W. Taking into account the maximum available power P.sub.E of the output stage (P.sub.E=U.sub.E.Math.I.sub.L), the coil current is determined and limited by the output stage voltage U.sub.E and the load resistance R.sub.W. With a constant load resistance R.sub.W, the maximum possible coil current is therefore determined by the output stage E, which in practice is dimensioned in such a way that a sufficient coil current can be provided within an intended load measuring range. For a larger force F.sub.u(overload force) outside this load measuring range, the output stage cannot provide sufficient compensation current, the coil movement cannot be compensated and the measuring resistor voltage cannot be meaningfully evaluated.

[0056] In contrast to this prior art arrangement, a scale in accordance with aspects of the present invention is switchable from the measuring mode (m) to an overload mode (u). For this purpose, the electrical load resistance R.sub.W is automatically reduced to enable a higher coil current I.sub.Lu with unchanged output stage power. The load resistance is preferably reduced by reducing the electrical measuring resistance R.sub.W1. Variousnot exhaustively listedsolutions for this are described in FIGS. 2-5, in which some repetitive elements shown in FIG. 1 have not been shown again.

[0057] As shown in FIG. 2, it is possible to switch from the measuring resistor W.sub.1 to an additional resistor W.sub.2 in such a way that the original measuring resistor W.sub.1 is completely removed from the resistor arrangement W or its load resistance R.sub.W. The coil current is now conducted through the additional resistor W.sub.2, the electrical resistance of which R.sub.W2 is smaller than R.sub.W1. The voltage to be measured (in the measuring mode it is U.sub.W1, in the overload mode it is U.sub.W2) is tapped here above the schematically shown switch. In overload mode, a lower voltage for the first A/D converter A.sub.1 is dropped at the additional resistor W.sub.2 compared to the previously effective measuring resistor W.sub.1, which not only increases the load capacity (a higher coil current can now flow), but also increases the measuring range. Knowing the respective effective electrical resistance values in the resistor arrangement W, the overload can be quantitatively determined with the help of the control unit mentioned in FIG. 1.

[0058] In the solution shown in FIG. 3, the load resistance R.sub.W is reduced by connecting an additional resistor W.sub.2 in parallel with the measuring resistor W.sub.1. The effects described for FIG. 2 apply here in the same way, wherein the measuring resistor W.sub.1 remains part of the resistor arrangement W.

[0059] FIG. 4 shows a particularly preferred embodiment of a scale according to the invention, which has already been explained in the above description. In the measuring mode (m), voltage values are tapped at the measuring resistor W.sub.1 and fed to the first A/D converter A.sub.1 and evaluated with the aid of a control unit C as shown in FIG. 1, which is not shown again here. When switching to overload mode (u), the measuring resistor W.sub.1 is short-circuited.

[0060] For quantitative detection of an overload force F.sub.u, an additional resistor W.sub.2 through which the coil current flows is provided in the resistor arrangement W shown the example of FIG. 4. An auxiliary voltage U.sub.H is tapped and evaluated as the additional resistor voltage U.sub.W2 for a second A/D converter A.sub.2 provided separately from the first A/D converter A.sub.1. The electrical resistance R.sub.W2 of the additional resistor W.sub.2 is significantly smaller than that of the measuring resistor W.sub.1, for example R.sub.W1 is 50 or 100 times greater than R.sub.W2. In the simplified representation according to FIG. 4 and neglecting the electrical resistance of the coil L, the load resistance in the overload mode (u) is only formed by the additional resistor W.sub.2, which allows a coil current I.sub.Lu 50 or 100 times greater (load extension). The additional resistance voltage U.sub.W2 generated by it and dropping at the additional resistance W.sub.2 can be quantitatively evaluated via the second A/D converter A.sub.2 and the control unit C (corresponding to control unit C in FIG. 1), whereby 50 or 100 times greater overload forces than in the measuring mode can be both compensated and quantitatively determined.

[0061] The variant according to FIG. 5 shows a measuring resistor W.sub.1 which is composed of two serial individual resistors which are not described further. One of these individual resistors can be short-circuited via a switch, which reduces the electrical measuring resistance R.sub.W1 and thus also the electrical load resistance R.sub.W.

[0062] As already shown in the example of FIG. 4, instead of the first A/D converter, a second A/D converter A.sub.2 can also be used independently of the first A/D converter in order to detect when a threshold value is exceeded, signalling an overload, and/or, in particular, to quantitatively measure overload forces.

[0063] FIG. 6 shows an example in which an additional second A/D converter A.sub.2 with an associated load measuring range B.sub.A2 is supplied with a voltage tapped at the resistor arrangement which differs from the resistance measuring voltage U.sub.W1 tapped for the measuring mode and results from the electrical coil resistance R.sub.L in the overload modeunlike in the example according to FIG. 4.

[0064] As in the example according to FIG. 4, the second A/D converter according to FIG. 6 can be used independently of the first A/D converter and both in measuring mode (m) and in overload mode (u) to monitor when threshold values are exceeded and to determine the acting forces F.sub.m, F.sub.u. The load measuring range B.sub.A2 can encompass the first load measuring range B.sub.A1 and be set sufficiently large to also quantitatively detect an overload that is no longer in the load measuring range B.sub.A1 of the first A/D converter, which is only provided here for evaluation in the measuring mode (m). The second load measuring range B.sub.A2 can also be specially tailored to voltage values above the first load measuring range B.sub.A1 in order to monitor threshold values or measure the overload forces only in this range. Depending on the type of load resistance reduction, in the circuit according to FIG. 6 at least one coil voltage U.sub.L generated by the coil resistance still drops at the second A/D converter A.sub.2 in the overload mode (u).

[0065] A modified version is shown in FIG. 7. Here, the second A/D converter A.sub.2 is supplied with the voltage that drops across the two resistors W.sub.1 (measuring resistor) and W.sub.2 (additional resistor) connected in series. If the measuring resistor W.sub.1 is reduced or short-circuited by switching to the overload mode (u) (analogous to the example of FIG. 4), the electrical resistance R.sub.W2 of the additional resistor W.sub.2 essentially determines the voltage supplied to the second A/D converter A.sub.2.

[0066] 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.

[0067] The directions referenced herein and in the following claims, namely, the x or transport direction, the z or height direction, and the y or width direction refer to the corresponding directions indicated in the drawings relative to the inspection device 1 as oriented therein.

[0068] 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). Rather than using an ordinal term to distinguish between commonly named elements, a particular one of a number of elements may be called out in the following claims as a respective one of the elements and thereafter referred to as that respective one of the elements.

[0069] 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.

[0070] 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.

DESIGNATIONS

[0071] W.sub.1 Measuring resistor [0072] W.sub.2 Additional resistor [0073] W Resistor arrangement [0074] A.sub.1 First A/D converter [0075] A.sub.2 Second A/D converter [0076] C Control unit [0077] E Output stage [0078] F.sub.m Force within a given load range [0079] F.sub.u Force outside the specified load range, overload force [0080] G Magnet [0081] I.sub.L Carrying coil current [0082] I.sub.Lu Overload coil current [0083] I.sub.Lm Coil current in measuring mode [0084] L Carrying coil [0085] B.sub.A1 Load measuring range of the first A/D converter A1 [0086] B.sub.A2 Load measuring range of the second A/D converter A2 [0087] R.sub.W1 Electrical resistance of the measuring resistor W.sub.1 [0088] R.sub.W2 Electrical resistance of the additional resistor W.sub.2 [0089] R.sub.W Electrical resistance of the resistor arrangement W (load resistance) [0090] R.sub.L Electrical resistance of the carrying coil L [0091] U.sub.W1 Measuring resistor voltage [0092] U.sub.W2 Additional resistor voltage [0093] U.sub.H Auxiliary voltage [0094] U.sub.E Output stage voltage [0095] U.sub.L Coil voltage [0096] (m) Index for measuring mode [0097] (u) Index for overloading mode