DE102017128078B4 - Twist sensor for a load cell - Google Patents

Abstract

Load cell (1) with a load cell body (2) comprising a head (3), a body (4) and a foot (5), wherein the head (3) has an upper end surface (8) which is essentially designed as a spherical surface and from body (4) is set off by at least one upper indentation (6), the body (4) is of essentially cylindrical design and the foot (5) has a lower end surface (9) which is essentially designed as a spherical surface and is separated from the body (4) by at least one lower notch (7) and a cable is arranged on the load cell body (2) for electrical contacting of the load cell body (2), characterized in that the load cell (1) has at least one rotation sensor (10).

Description

The invention relates to a load cell with a load cell body, with a head, a torso and a foot, the head having an upper end surface designed essentially as a spherical surface and being separated from the torso by at least one upper indentation, the torso being essentially cylindrical and the foot has a lower end surface designed essentially as a spherical surface and is set off from the body by at least one lower indentation.

Load cells, for example pendulum load cells for use in road vehicles, usually consist of a measuring element covered with strain gauges, which is referred to below as the load cell body.

The load cell body is made of a high-strength metallic material, usually steel, and comprises a head, a base and a body arranged therebetween. Strain gauges are arranged on the surface of the load cell body at a suitable point, usually on the essentially cylindrical body. These strain gauges, usually constantan or karma strain gauges, are usually wired electrically as a full Wheatstone bridge.

A separate housing can be arranged around the load cell body to protect the strain gauges from water or moisture or from dirt. An adjustment chamber is also attached to this housing, in which there is electronics for the electrical adjustment of the load cell, for example for determining the zero point, the characteristic value, the temperature behavior etc., and optionally a signal processing device. This adjustment chamber is also used to protect the electronic components from moisture and dirt.

In order to achieve a targeted load introduction from the end faces of the head and the foot into the torso, in particular in the direction of a web or a membrane, punctures running rotationally symmetrically around the longitudinal axis of the load cell body are provided, through which the head from the torso and the torso can be separated is removed from the foot.

The problem with these load cells is that movement of the goods to be weighed, e.g. due to the application or removal of loads, can cause rotation around the vertical axis of the load cell body used. The load cell bodies are electrically connected to a higher-level controller by a cable. When the load cell body rotates, the cable wraps around the load cell body and can ultimately break away. Furthermore, such a rotation of the load cell body can lead to measurement errors, in particular the reproducibility error increases.

the WO 2005/024357 A1 discloses a mechanical anti-rotation device, the peripheral surface of the foot having at least one essentially vertical groove which can interact with a respective projecting element provided on the lower plate when the load cell is installed.

The disadvantage of this solution is that a very high force acts on the protruding element and the load cell body is distorted, which can lead to measurement errors. Furthermore, this element can break off, which means that there is no longer any anti-twist protection.

It is the object of the present invention to provide a load cell of the type mentioned at the outset, which enables a reliable detection of a twisting of a load cell body.

This object is achieved according to the invention with a load cell of the type mentioned at the outset in that the load cell has at least one rotation sensor.

The rotation sensor is a non-contact measuring sensor, in particular an optical, magnetic, inductive or capacitive sensor. As a result, the load cell or the load cell body can rotate about its vertical axis within certain limits without measurement errors occurring or the load cell body becoming tense. Furthermore, a non-contact measuring sensor enables instantaneous values to be displayed for precise monitoring of the current position of the load cell body. For this purpose, an operator can be shown on a control display whether the load cell body is still in its basic position or whether it has moved. In addition, a threshold value can be displayed to the operator, whereby the load cell body may move within these limits without there being a risk of measuring errors. Furthermore, the load cell can send a warning signal to a higher-level controller if the load cell has rotated too far. This prevents the cable from being torn off the load cell body.

The warning signal can also be multi-stage and the operator can see the current signal on a control display in the form of a traffic light system Show torsion of the load cell body. For example, the operator is signaled with a first color, preferably green, that the load cell body is within the threshold value range. A second color, preferably yellow, informs the operator that the load cell has rotated and is at the limit of the threshold value range and that the load cell should be rotated back to rule out measurement errors. A third color, preferably red, signals the operator that the load cell has twisted to the point where there is a risk of the cable being torn from the load cell body. In addition, the load cell can refuse to display a weighing result if the load cell body has rotated too far and there is a risk that the cable could be torn off.

This optical warning system can also be arranged on the load cell. As a result, an operator can quickly see whether a rotation around the vertical axis of the load cell body has taken place.

The rotation sensor is preferably arranged on the load cell body. For this purpose, there can be a recess in the load cell body in which the sensor is inserted. A separate housing is typically arranged around the load cell body. The rotation sensor can thus also be arranged in the housing.

In a further embodiment, the rotation sensor can determine its position relative to the earth's magnetic field. For this purpose, the load cell has a 3D magnetic sensor, with the magnetic sensor preferably having its own sensor for each of the three magnetic axes, in particular a Hall sensor in each case. This means that a reference object can be dispensed with. However, it is also advantageous here if at least one reference object is present.

In a further embodiment, a base plate and a top plate are arranged on the weighing cell, the base plate being designed to accommodate the foot and the load to be weighed being supported on the top plate. The base plate and the top plate can have stops to prevent the load cell body from tilting. A tilting of the load cell body would result in overloading of the load cell body, which would result in damage to it.

In a further embodiment, at least one rotation sensor, in particular an optical sensor or a magnetic sensor, in particular a Hall, AMR, GMR or TMR sensor, is arranged in or on the load cell body or in or on the housing of the load cell body. The base plate and/or the top plate has at least one ferromagnetic and/or electrically conductive and/or optical reference object, in particular a magnet or an LED. The reference object is thus arranged outside of the load cell body or outside of the housing of the load cell body. If the load cell body rotates, the influence of the reference object on the rotation sensor changes. This change is detected by the rotation sensor and can be communicated to the user in digital form, for example. For example, the rotation sensor can detect the absolute position of the load cell body or when a rotation threshold value has been reached.

In a further refinement, the rotation sensor detects the reference object in a basic position. The basic position here is the installation position of the load cell body, in which the load cell body has not experienced any rotation and the rotation sensor is positioned in the radial direction in the center relative to the reference object. In this case, the reference object and the rotation sensor are arranged opposite one another in the basic position. To ensure quick and easy installation, there can be an optical positioning aid on the base plate, on the top plate, on the load cell, on the load cell body and/or on the housing, which indicates the basic position of the load cell body. The reference object has an extent in the radial direction which corresponds to the permitted rotation of the load cell body, in particular the reference object has a length in the radial direction of greater than 1 mm, preferably greater than 5 mm, particularly preferably greater than 8 mm. As soon as the load cell body rotates further than the threshold value range specified by the reference object, the reference object is no longer detected by the rotation sensor and the rotation sensor sends a warning message to a higher-level controller, for example, that the load cell body has rotated too far and the load cell body must be rotated back because otherwise the cable could be torn off.

In a further embodiment, the reference object has different marking positions in the radial direction, at which, for example, differently shaped magnetizable material is present. The rotation sensor detects the differently shaped materials, the different shapes of the material at the marking positions leading to different field distributions, so that the absolute position can be determined using the output signal of the rotation sensor. The output signal can, for example, be a scalar value for the field strength speak, but it is also possible to record one or more field directions.

For example, the reference object consists consistently of a ferromagnetic material, in particular iron, which is processed at the marking positions, in particular by drilling, milling, punching, etc. The reference object can hereby have a step-like progression or a coding in the radial direction, for example. Furthermore, it is possible, for example in the case of an optical rotation sensor, for different LEDs to be arranged in the radial direction, which LEDs have different radiation intensities or different wavelengths, for example. Furthermore, it is conceivable that the LEDs are arranged at different distances from the rotation sensor. Alternatively, the marking positions can have a different degree of reflection.

In a further refinement, the reference object can be connected in one piece to the base plate and/or top plate. In the basic position, the rotation sensor is positioned in the middle of the reference object. Advantageously, the reference object has at least two marking positions which are designed differently in terms of their size, shape and/or arrangement relative to the center point of the reference object, so that they influence the rotation sensor differently from one another. For example, it can also be determined in which direction the load cell body rotates.

In a further refinement, the rotation sensor detects the reference object in a rotation position. The twisted position is the position of the load cell body at which measurement errors or the cable can break due to the rotation of the load cell body. In this configuration, the load cell body is inserted into the load cell in the basic position. In order to ensure quick and easy installation, there can be a visual positioning aid on the base plate and/or on the top plate, which indicates the basic position of the load cell body. In particular, the visual positioning aid can be a marking in the form of a recess or a printed arrow. In the basic position, the reference object is not detected by the rotation sensor. As soon as the load cell body rotates further than a permitted threshold value range, the reference object is detected by the rotation sensor and the rotation sensor sends a warning message to a higher-level controller, for example, that the load cell body has rotated too far and the load cell body must be rotated back, otherwise the cable could be torn off . In this embodiment, too, it is possible for the reference object to have different marking positions in order to be able to determine an absolute position of the load cell body or to be able to output different warning messages.

In a further embodiment, the length of the reference object in the radial direction is adapted to the length of the cable. For example, the cable has a length that allows the load cell body to rotate more than 30° about the vertical axis of the load cell body. The reference object extends over an area that covers a rotation of the load cell body of 60°. This allows the load cell body to rotate 30° in both directions. This prevents the load cell body from rotating too far and tearing off the cable.

In a further embodiment, the cable for the electrical supply of the rotation sensor is arranged inside the housing. This eliminates the need for separate or external cables. The cable is preferably routed within the housing to the adjustment chamber. This means that only one cable is required to supply the load cell with electricity, which is also used to supply the rotation sensor with electrical energy. A sensor output signal can also be output via this connection. The sensor output signal can be output in various ways, for example as a current or voltage signal, either analog or digital, in particular also as a PWM signal.

In a further embodiment, at least two rotation sensors are arranged opposite one another on the load cell or on the housing, with a first rotation sensor detecting a first reference object in a basic position and a second rotation sensor detecting a second reference object in a rotation position. This enables two-channel, fully redundant acquisition. Alternatively, it is also possible for the first and the second rotation sensor to detect the first and the second reference object in a basic position or in a rotation position.

• 1: Einen Querschnitt der Wägezelle mit einem Verdrehsensor und einem Referenzobjekt
• 2: Einen Schnitt durch das Gehäuse des Wägezellenkörpers mit einem Verdrehsensor und einen mit Markierungspositionen versehenes Referenzobjekt
• 3: Einen Schnitt durch die Wägezelle mit zwei Verdrehsensoren

Preferred exemplary embodiments of the device according to the invention are presented below with reference to figures.

• 1 : A cross-section of the load cell with a twist sensor and a reference object
• 2 : A section through the housing of the load cell body with a twist sensor and a reference object provided with marking positions
• 3 : A section through the load cell with two twist sensors

1 shows a load cell 1 with a load cell body 2, comprising a head 3, a body 4 and a foot 5, wherein the head 3 has an upper end face 8 essentially designed as a spherical surface and is separated from the body 4 by at least one upper recess 6, which Body 4 is essentially cylindrical and foot 5 has a lower end face 9 essentially designed as a spherical surface and is separated from body 4 by at least one lower recess 7 and a cable (not shown) is arranged on load cell body 2 for electrical contacting of load cell body 2 , wherein the load cell 1 has at least one rotation sensor 10 .

To protect the strain gauges from water or moisture or from dirt, a separate housing 11 is arranged around the load cell body 2 , with the rotation sensor 10 being positioned within the housing 11 . An adjustment chamber 12 is also attached to the housing, in which there is electronics for the electrical adjustment of the load cell, for example for determining the zero point, the characteristic value, the temperature behavior, etc. and optionally a signal processing device. This adjustment chamber 12 is also used to protect the electronic components from moisture and dirt.

Furthermore, a base plate 13 and a top plate 14 are arranged on the load cell 1, the base plate 13 being designed to accommodate the foot 5 and the load to be weighed being supported on the top plate 14. The base plate 13 and the top plate 14 can have stops so that the weighing cell body 2 can be prevented from tilting. A tilting of the load cell body 2 would result in an overstressing of the load cell body 2, with the result that there would be a risk of damage to it.

A torsion sensor is arranged on the housing 11 of the load cell body 2 and can be, in particular, a magnetic sensor, a Hall sensor or an optical sensor. The base plate 13 has at least one ferromagnetic and/or electrically conductive and/or optical reference object 15, in particular a magnet or an LED. The load cell body 2 is in the basic position and the rotation sensor 10 is positioned centrally above the reference object 15 . Thus, the rotation sensor 10 and the reference object 15 are arranged opposite one another in the basic position. In this case, the reference object 15 has an extent in the radial direction which corresponds to the permitted rotation about the vertical axis 22 of the load cell body 2 . As soon as the load cell body 2 rotates further than a threshold value range specified by the reference object 15, the reference object is no longer detected by the rotation sensor 10 and the rotation sensor 10 sends a warning message to a higher-level controller, for example, that the load cell body 2 has rotated too far and the load cell body 2 must be turned back, otherwise the cable could be torn off.

2 shows a load cell 1 according to FIG 1 , A section through the housing 11 of the load cell body 2 being shown here. As a result, both the rotation sensor 10 and the reference object 15 are shown with marking positions 16a, 16b, 16c, 16d, 16e. The load cell body 2 is in the basic position and the rotation sensor 10 is positioned centrally above the reference object 15 . The reference object 15 has at least two marking positions 16a, 16b, 16c, 16d, 16e. As a result, both the direction of rotation of the load cell body 2 and the position can be determined with sufficient accuracy. The reference object 15 with the marking positions 16a, 16b, 16c, 16d, 16e can be produced by drilling, milling, punching, etc. The reference object 15 has a coding, for example. Furthermore, it is possible for the reference object 15 to be formed in one piece with the base plate 13 , for example by drilling holes of different depths in the base plate 13 . As soon as the load cell body 2 rotates about its vertical axis 22, the influence of the reference object 15 on the rotation sensor 10 changes. This change is detected by the rotation sensor 10 and can be communicated to the user in digital form, for example. In this way, the rotation sensor 10 can detect the absolute position of the load cell body 2 or when a threshold value has been reached.

It is also possible, for example, for the direction of magnetization of the marking positions 16a, 16b, 16c, 16d, 16e to be detected. This reduces sensitivity to mechanical tolerances. For this purpose, each marking position 16a, 16b, 16c, 16d, 16e can be magnetized in different directions. By detecting the direction of the magnetic field influenced thereby, the different marking positions 16a, 16b, 16c, 16d, 16e can then be distinguished on the basis of the output signal of the rotation sensor 10.

3 shows a section of the load cell 1. Here, the foot 5, the lower recess 7, the housing 11 and the base plate 13 are shown. A first rotation sensor 17 and a second rotation sensor 18 are arranged in the housing 11 . Furthermore, a first reference object 19, a second Refe reference object 20 and a third reference object 21 in the base plate 13 integrated. The first rotation sensor 17 and the second rotation sensor 18 are arranged opposite one another, with the first rotation sensor 17 detecting the first reference object 19 in a basic position and the second rotation sensor 18 detecting the second and third reference objects 20, 21 in different rotation positions. The second reference object 20 is only detected by the second rotation sensor 18 when the load cell body 2 rotates clockwise or to the right, and the third reference object 21 is only detected by the second rotation sensor 18 when rotating counterclockwise or to the left . Due to this structure, the direction of rotation of the load cell body 2 can be surely recognized. The distance between the second rotation sensor 18 and the second and third reference objects 20, 21 in the basic position preferably corresponds to half the width of the first reference object 19.

Reference List

1

load cell

2

load cell body

3

head

4

hull

5

Foot

6

Upper puncture

7

Lower puncture

8th

upper end face

9

lower end face

10

twist sensor

11

Housing

12

adjustment chamber

13

base plate

14

headstock

15

reference object

16a

marker position

16b

marker position

16c

marker position

16d

marker position

16e

marker position

17

first twist sensor

18

second twist sensor

19

first reference object

20

second reference object

21

third reference object

22

vertical axis

Claims (17)

Load cell (1) with a load cell body (2) comprising a head (3), a body (4) and a foot (5), wherein the head (3) has an upper end surface (8) which is essentially designed as a spherical surface and from body (4) is set off by at least one upper indentation (6), the body (4) is of essentially cylindrical design and the foot (5) has a lower end face (9) which is essentially designed as a spherical surface and extends from the body (4) through at least one lower notch (7) and a cable is arranged on the load cell body (2) for electrical contacting of the load cell body (2), characterized in that the load cell (1) has at least one rotation sensor (10). load cell (1) after claim 1 , characterized in that the rotation sensor (10) is a non-contact sensor, in particular an optical, magnetic, inductive or capacitive sensor. load cell (1) after claim 1 or 2 , characterized in that the rotation sensor (10) is arranged on or in the load cell body (2). Load cell (1) according to one of the preceding claims, characterized in that a separate housing (11) is arranged around the load cell body (2). load cell (1) after claim 4 , characterized in that the rotation sensor (10) is arranged on or in the housing (11). Load cell (1) according to one of the preceding claims, characterized in that the rotation sensor (10) determines its position relative to the earth's magnetic field. Load cell (1) according to one of the preceding claims, characterized in that a base plate (13) and a top plate (14) are arranged on the load cell (1), the base plate (13) being designed to accommodate the foot (5) and the load to be weighed is supported on the top plate (14). load cell (1) after claim 7 , characterized in that the base plate (13) and/or the top plate (14) has at least one ferromagnetic and/or electrically conductive and/or optical reference object (15). load cell (1) after claim 8 , characterized in that the rotation sensor (10) detects the reference object (15) in a basic position. load cell (1) after claim 8 or 9 , characterized in that the rotation sensor (10) detects the reference object (15) in a rotated position. Load cell (1) according to one of Claims 8 until 10 , characterized in that the length of the reference object (15) is adapted in the radial direction to the length of the cable. Load cell (1) according to one of Claims 8 until 11 , characterized in that the reference object (15) has at least two different marking positions (16a, 16b, 16c, 16d, 16e). load cell (1) after claim 12 , characterized in that the marking positions (16a, 16b, 16c, 16d, 16e) are magnetized in different directions. load cell (1) after claim 12 or 13 , characterized in that the marking positions (16a, 16b, 16c, 16d, 16e) have a stepped profile and/or a coding. Load cell (1) according to one of the preceding claims, characterized in that the load cell (1) has an optical positioning aid. Load cell (1) according to one of the preceding claims, characterized in that at least two rotation sensors (17, 18) are arranged opposite one another on the load cell (1) or on the housing (11), a first rotation sensor (17) detecting a first reference object ( 19) is detected in a basic position and a second rotation sensor (18) detects at least one further reference object (20, 21) in a rotation position. load cell (1) after Claim 16 , characterized in that the base plate (13) and/or the top plate (14) have at least a second and a third reference object (20, 21), the second and the third reference object (20, 21) each being in different rotational positions from the second rotation sensor (18) are detected.

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