EP2145162A1

EP2145162A1 - Scale

Info

Publication number: EP2145162A1
Application number: EP08733811A
Authority: EP
Inventors: Jevgenij Mannhart; Cyrill RÖTHLIN; Marc Robert; Jérôme BERNHARD
Original assignee: Carag AG
Current assignee: Carag AG
Priority date: 2007-05-04
Filing date: 2008-04-23
Publication date: 2010-01-20
Also published as: US20100133016A1; WO2008134906A1

Abstract

The invention relates to a scale having a base plate (1), a bed plate (2) located at a distance above the base plate (1) for supporting an object to be weighed, and elastic spacing elements (3) located between the base plate (1) and the bed plate (2). Said scale further comprises a weighing means for determining the weight of the object, said weighing means being at least one inductive proximity sensor (10, 20, 4). Said scale is robustly constructed and allows great flexibility in the external design of the scale.

Description

Technical area

The invention relates to a balance according to the preamble of patent claim 1.

State of the art

In the prior art, a wide variety of scales are known. Most of them either have a mechanical counterweight or they have springs or flex beams to measure the weight load. Furthermore, it is known to use proximity sensors to set the zero value of the balance or to compensate for an uneven load on the balance.

Thus, DE 38 119 42 A1 discloses an electronic balance with corner load sensors, which has a first measuring arrangement with a coil and a position sensor for measuring the weight and a second measuring arrangement with a further coil for measuring the deflection of the weighing pan. The weight measurement is carried out by the detection of a compensation current, which is required to generate a compensation force to compensate for the weight of the sample. For this purpose, a movement mediated by weighing detected by the position sensor and sent a corresponding signal to the coil for generating the compensation force. The measurement of the deflection of the shell by the second coil is made to compensate for errors in weight measurement due to unequal loading of the scale. The two measurements are independent of each other and are only connected by a signal processing system. In US 5,773,767, for example, a balance with a bending beam and a Hall sensor is shown, which performs an automatic zero adjustment after removal and replacement of a weighing platform.

The patent US 4,503, 922_ relates to an electronic personal scale with a flat coil sensor for distance determination. Here, arms or struts are provided between a weighing surface and a base plate, which are connected to a spring device and transmit a movement of the arms by the action of a gravitational force on the sensor. The sensor essentially consists of a stationary plate on which one or two coil circles are provided and a movable plate on which the arms act.

US 5 717 167 describes a vehicle scale with an inclinometer, which compensates for a possible inclination of the balance. Also in WO 03/007072, the skew, here a forklift, measured to correct a weight measurement.

No. 4,507,742 describes an aircraft weighing system with an inclinometer pair for determining the weight of the aircraft.

In the case of large scales for vehicles or aircraft, the maximum load capacity is in the foreground. Especially in household and personal scales, however, the requirements for the external design are very large. Unfortunately, the measuring technology impairs the freedom of design, since springs, bending beams, electronics and any cabling must not be visibly integrated into the balance as far as possible from the outside. Furthermore, the scale should be as robust as possible in order to be able to be transported and to withstand possible impacts or other impairments.

Presentation of the invention It is therefore an object of the invention to provide a balance which is robust and allows the greatest possible flexibility in the external design of the balance.

This object is achieved by a balance with the features of patent claim 1.

The scale according to the invention comprises a base plate, a support plate arranged at a distance above the base plate for supporting an object to be weighed, resilient spacer elements which are arranged between base plate and support plate and a weighing means for determining the weight of the object. The weighing means is formed by at least one inductive proximity sensor which comprises an electrical coil and a metallic, ferromagnetic or paramagnetic reference plate, wherein the at least one coil is arranged in the one of support plate or base plate and the reference plate in the other of support plate or base plate is arranged or formed thereof. That is, the coil is arranged either in the support plate or the base plate and the reference plate is arranged in each case in the other of these two plates or is formed by this.

This scale requires relatively few and only small items, which are also hardly susceptible to interference. Furthermore, they are inexpensive. The individual parts need not be mechanically or electronically connected to one another for the purpose of evaluating the measurement, so that they hardly influence the external shape of the balance. This scale is suitable in particular, but not exclusively as a personal scale or household scale. The scale is particularly suitable for weighing non-stationary objects, such as babies.

Preferably, the proximity sensor uses the same measuring principle as disclosed in EP 0 913 857. There, a method and a device for the adjustment of a bonding head of a bonder are described, which use an inductive distance measurement as the measuring principle.

Preferably, the spacer elements are arranged distributed in an edge region of the base plate and the support plate and the at least one proximity sensor is located in the middle region of the base plate and the support plate. Since an inductive proximity sensor is used, even the smallest distance deviations can be measured.

Since the weighing means consists only of inductive proximity sensors and these from flat coils integrated in a printed circuit board as well as associated reference plates, the balance is very robust. It is advantageous that the inductive proximity sensors allow a contactless measurement and no cable connections are necessary. As a result, the support plate or all parts which come into contact with the object to be measured can be arranged completely separate from all the electronics.

Even with non-elastic provision of the support plate can be achieved in a simple manner Zero adjustment of the balance by the new distance between the coil and reference plate is taken as zero value. Thanks to the use of several, in particular three or four, coils, the inclinations of the support plate to the solder as well as to the base plate can be automatically detected and compensated. Thanks to the relatively small proximity coils, which in addition can all be arranged on a common printed circuit board, cabling is unnecessary, which would have to be laid over long distances along the scale. In addition, no mechanical measuring means are necessary. The weighing means thus minimally influences the shape of the balance. In particular, transparent support plates and base plates can be used.

Further advantageous embodiments will become apparent from the dependent claims.

Brief description of the drawings

The subject of the invention will be explained below on the basis of preferred exemplary embodiments, which are illustrated in the attached drawings. Show it:

Figure 1 is a view of a scale according to the invention according to a first Embodiment from above;

Figure 2 is a side view of the balance according to Figure 1;

FIG. 3 shows a cross section through the balance according to FIG. 1;

Figure 4 is an enlarged view of a detail according to Figure 3;

FIG. 5 shows a side view of a balance according to a second embodiment of the invention;

6 shows a cross section through the balance according to Figure 5 and

FIG. 7 is an enlarged view of a detail according to FIG. 6.

Ways to carry out the invention

FIGS. 1 to 4 show a first exemplary embodiment of the balance according to the invention. It has a base plate 1 and a support plate 2 arranged above it. Between the two plates 1, 2 resilient spacers 3 are arranged so that between the plates 1, 2, a cavity 7 is formed. When loading the support plate 2 with an object to be weighed, the spacer elements 3 are compressed and the distance between the support plate 2 and the base plate 1 is reduced.

The two plates 1, 2 are rectangular in this example, wherein the support plate 2 is larger than the base plate 1. However, they can have any one and different shape. They can also be made of any material, the support plate 2 must be stable enough to carry an object to be weighed without deformation. In this example, the platen 2 and the base plate 1 are made of metal. However, they can also be made of plastic or glass, for example. The base plate 1 is preferably substantially planar. formed in parallel. The support plate 2 may be plane-parallel, form a Aufiiahmeschale or have another optimized for receiving an object to be weighed shape.

The resilient spacer elements 3 may also be arbitrarily shaped, with their elastic recoverability defines the maximum load capacity of the balance. Preferably there are four spacer elements 3 which are distributed in the outermost areas of overlap of the base and platen 1, 2, i. in their peripheral areas. They preferably form the vertices of a common rectangle. However, it is also possible for there to be three or, depending on the shape of the two plates 1, 2 or the spacer elements 3, one or two or more than four spacer elements.

The spacer elements 3 are in this example metal diaphragm springs, which are bent from a continuous sheet and provided with concentric areas. But it can also use leaf springs, coil springs or other suitable spring elements with sufficiently large elastic restoring force.

In the example shown here, the spacers 3 are mounted on the base plate 1 and the support plate 2 is loosely on them. However, the support plate 2 can also be firmly connected to the spacer elements 3 or the spacer elements 3 can be mounted on the support plate 2 and rest loosely on the base plate 1.

The balance further comprises a weighing means for determining the weight of the object to be weighed. According to the invention, this weighing means is at least one inductive proximity sensor. The balance therefore has a sensor unit 4 with a printed circuit board 40. On the circuit board 40, four electric coils 41, 42, 43, 44 are arranged, forming four corners of a square. The sensor unit 4 is arranged in this example in the central region, more precisely here in the middle of the base plate 1 and the support plate 2. However, it can also be arranged at a different location. Likewise, the individual coils 41, 42, 43, 44 may be arranged on different circuit boards instead of on a common circuit board 40, which are arranged distributed over the base plate 1 or the support plate 2. Furthermore, another number of Coils are used, in particular one or three. In the case of only one coil, however, only a weight measurement, but not a skew correction can be performed. This requires three sensors.

The coils 41, 42, 43, 44 are preferably of identical construction and in this exemplary embodiment they are flat coils formed from printed conductors, as described in EP 0 913 857. Each coil forms part of a proximity sensor. The counterpart to this is formed by a reference plate 20, which is metallic, ferromagnetic or paramagnetic. It may, as shown in Figure 4, be part of the support plate 2, the corresponding surface of the plate may be corresponding metallized or coated or the reference plate may be attached to the support plate 2. In addition, as shown in this example, a common reference plate 20 can be used for all proximity coils 41, 42, 43, 44 or each coil can be assigned its own reference plate.

The circuit board 40 is mounted on a cavity 8 of the base plate 1 on this, in which the arranged on the circuit board 40, not shown here electronic components can protrude. The printed circuit board 40 is connected to a transmitter 5, which has a display unit 50. The evaluation electronics 5 can also be integrated on the printed circuit board 40 and the display unit 50 can be connected directly afterwards or, as shown here, at a distance thereto. The connection between the printed circuit board 40 and the display unit 50 is preferably carried out by means of electrical cables, which extend in a connecting channel 6 in the example shown here. However, an infrared signal transmission, radio or other wireless signal transmission means may be used.

As can be seen in FIGS. 5 to 7, the printed circuit board 40 can also be fastened to it via a cavity 8 of the support plate 2 and the reference plate 10 or plates are arranged in or on the base plate 1. In this case, the spacer elements 3 are preferably likewise fastened to the support plate 2.

Regardless of whether the proximity coils 41, 42, 43, 44 in or on the support plate 2 or in or on the base plate 1, the operation of the balance is the same and corresponds to the measuring principle described in EP 0 913 857: The coils are energized with an alternating current and generate a magnetic field. If the distance between the reference plate 10, 20 and coil 41, 42, 43, 44 is changed by resting an object to be weighed on the support plate 2, then the ohmic resistance or the inductance of the coil changes as a function of the change in distance.

A possible measuring principle is as follows: the four signals U1, U2, U3, U4 of the four coils 41, 42, 43, 44 are summed in a sum amplifier, in parallel a possible inclination of the plate in comparison with the vertical is calculated in a tilt calculator, for example, by forming the differences between the signal of the fourth coil with the third and the first coil and the sum or difference of these two differences as a correction value in a correction calculator. In the correction calculator, the sum of the summation amplifier is corrected with the correction value, thereby obtaining a weight signal which takes into account a possible skew of the plate. This signal can now be provided with a corresponding calibration value and displayed as a kg or pound indication on the display 50 or forwarded to a printer or to another electronic unit. However, the scale can also be used without skew correction.

The inventive scale is thus robust and allows a great deal of flexibility in the external design of the balance.

LIST OF REFERENCE NUMBERS

1 base plate

10 lower reference plate

2 platen

20 upper reference plate

3 spacer element

4 sensor unit

40 circuit board

41 first proximity sensor

42 second proximity sensor

43 third proximity sensor

44 fourth proximity sensor

45 summing amplifiers

46 correction calculator

47 inclination calculator

5 evaluation electronics

50 display windows

6 connecting channel

7 first cavity

8 second cavity

Claims

claims

1. Libra with a base plate (1), a spaced above the base plate (1) arranged support plate (2) for supporting an object to be weighed, with resilient spacer elements (3) which are arranged between the base plate (1) and support plate (2) , and weighing means for determining the weight of the object formed by at least one inductive proximity sensor (10, 20, 4), characterized in that the at least one proximity sensor (10, 20, 4) comprises an electrical coil (41, 42 , 43, 44) and a metallic, ferromagnetic or paramagnetic reference plate (10, 20), wherein the at least one coil (41, 42, 43, 44) is arranged in the one of support plate (2) or base plate (1) and the reference plate (20) is arranged in the other of support plate (2) or base plate (1) or is formed thereof.

2. Scales according to claim 1, wherein the spacer elements (3) are arranged distributed in an edge region of the base plate (1) and the support plate (2) and that the at least one proximity sensor (1, 20, 4) in the central region of

Base plate (1) and the support plate (2) is arranged.

3. Scales according to one of claims 1 or 2, wherein exactly four proximity sensors are present.

4. A balance according to claim 3, wherein the four proximity sensors have a common reference plate (10, 20).

5. A balance according to any one of claims 3 or 4, wherein the four proximity sensors are arranged in a square.

6. A balance according to one of the preceding claims, wherein the proximity sensors are connected to a common evaluation electronics (5) which adds the signals of the four sensors and an average value and which forms the differences of the signals from at least three sensors and these as correction value offset against the mean.

7. Scales according to one of the preceding claims, wherein the resilient spacer elements (3) are diaphragm springs.

8. Scales according to one of the preceding claims, wherein exactly four spacer elements (3) are present, which form vertices of a common rectangle.