EP2073343A1 - Sensor - Google Patents

Abstract

The sensor has an evaluation unit that detects a position of a piston (12) of a working cylinder (10) and that provides a signal representing the piston position. A power supply unit (28) is provided for power supply of the evaluation unit. The supply unit includes piezo-elements (34, 36) and energy converter magnets (32) i.e. permanent magnets, which act on the piezo-elements during movement of the piston. The signal is wirelessly transmitted from the sensor to a superordinated controller. The magnets exert pressure on the piezo-elements during movement of the piston.

Description

The invention relates to a magnetic or inductive sensor for detecting a piston position according to the preamble of claim 1, as well as the use of such a sensor.

Such sensors are often arranged on a housing of a working cylinder and have for accurate position determination by contactless detection of the position of z. B. pneumatic or hydraulic piston proven within the working cylinder. Such a sensor is for example from the DE 10 2006 008 157 A1 known. This known sensor can detect two specific piston positions. Simpler sensors detect only one piston position at a time.

The electrical supply of the sensor and the transmission of the switching signal via an electrical line. Laying the connecting cables is very time- and material-consuming, since the sensors are typically used in industrial robots and a large number of such sensors have to be used on a single robot. Harnesses with 20 to 30 lines are common. The cables are then guided via drag chains on the moving parts. Line breaks are the most frequent cause of failure with these sensors (about 80% of failures). The connection between sensor housing and connection cable is also a weak point in terms of tightness.

There are some manufacturers demonstrators or pilot plants in which wireless sensors are operated. For example, ABB offers wireless sensors whose power supply is inductively coupled through huge conductor loops, with the conductor loops spanning the entire robot cell. Such conductor loops are very space, assembly and costly and the radiated energy is very high.

Next battery-powered wireless sensors are known, which have the known disadvantages such as limited life and thus increased maintenance costs and no adequate system availability. With the large number of sensors required on an industrial robot, this can not be achieved.

On this basis, it is an object of the invention to provide an improved magnetic or inductive sensor for detecting a piston position from outside of a working cylinder, which can work wirelessly and is simple, compact and inexpensive.

This object is achieved by a sensor having the features of claim 1.

The magnetic or inductive sensor according to the invention has an evaluation unit for detecting a piston position along a stroke of a piston, wherein the piston carries a permanent magnet formed as a piston magnet whose position can be detected by the evaluation and wherein the evaluation unit can deliver a piston position representative signal. The sensor is characterized in that a power supply unit is provided for supplying energy to the evaluation unit, which has at least one piezoelectric element and at least one energy converter magnet which acts on the piezoelectric element when the piston moves and the signal can be transmitted wirelessly from the sensor to a higher-level control.

During a movement of the piston, a force is exerted on the energy converter magnet via the piston magnet and through the magnetic coupling. This force is then transmitted to the piezoelectric element and generates a voltage in a conventional manner on the piezoelectric element. The energy thus generated can be used to operate the sensor, that is to detect the piston position and to transmit a signal representing the piston position to a receiver of a higher-level control.

Due to the sensor-own, self-sufficient energy supply, neither a battery nor a connection cable is necessary for the operation of the sensor. This not only considerably reduces the installation and installation effort, but neither drag chains nor cable ducts are required. As a result of the possible omission of all cables for the sensor according to the invention, the availability of the system in which the sensors are used is considerably increased and downtimes of the system are reduced since failure due to line breaks can no longer occur. In addition, new applications with freely movable, ie unbound magnetic sensors are possible.

Furthermore, a complete encapsulation of the sensor is possible, which is particularly advantageous in installations for the food industry in which aggressive cleaning agents are used or even in applications with explosion protection conditions.

Another advantage is the associated with the freedom of the cable simple replacement of sensors.

A voltage generation at the piezoelectric element takes place when a compressive force or a tensile force acts on the piezoelectric element. The deformation of the piezoelectric element takes place in the micron range and is therefore negligible. Thus, the sensor can be formed without moving parts, whereby no mechanical wear occurs. The energy generated is also largely independent of the speed of the piston magnet and thus largely independent of the speed with which the piston moves in the working cylinder. from that also results in a long service life, and compact designs are feasible. This opens up the possibility of the sensor according to the invention in a known manner (such as in DE 196 43 413 A1 or DE 196 53 222 A1 described) to place in existing mounting grooves on a working cylinder.

In development of the invention, the effective direction of the energy converter magnet is perpendicular to the stroke. The energy converter magnet is then attracted while passing the piston magnet in one phase to the piston magnet and repelled in another phase of the piston magnet, so that both processes can be used to generate energy. Advantageously, the magnetic orientation of the energy converter magnet is perpendicular to the stroke. It should be noted that the power generation is independent of the polar direction of the piston magnet and the energy converter magnet, wherein advantageously the magnetic orientation of the piston magnet is in the direction of the stroke.

Also, the energy converter magnet is preferably a permanent magnet.

In a structurally simple variant of the energy converter magnet exerts pressure on the piezoelectric element during movement of the piston. This can be advantageously increased by the energy converter magnet exerts the pressure via a lever on the piezoelectric element.

An increase of the pressure can also be achieved in that the energy converter magnet is mounted linearly movable and the energy converter magnet is moved along its storage during movement of the piston magnet and the piezoelectric element forms a stop. When the energy converter magnet stops the moment of inertia of the energy converter magnet additionally acts on the piezoelectric element, which can induce a significant voltage pulse in the piezoelectric element, as usually the piston on working cylinders of industrial robots and the like move very fast and the energy converter magnet, especially if its polar direction perpendicular to the piston magnet is and he is linearly displaceable in or against the polar direction, moves very abruptly and accordingly strongly strikes the piezoelectric element, which induces a correspondingly high voltage.

Alternatively, the energy converter magnet could exert a bending force on the piezoelectric element during movement of the piston in order to generate an electrical voltage on the piezoelectric element.

With particular advantage, a plurality of piezoelectric elements and / or energy converter magnets may be provided in order to increase the energy yield. Thus, for example, an energy converter magnet could be sandwiched between two piezoelectric elements, so that when passing the piston magnet in a phase of movement of the piston, a force on the one piezoelectric element and in a further phase of the piston movement a force in the other direction is exerted on the other piezoelectric element ,

In a further development of the invention, the effect of the energy converter magnet can be used on the piezoelectric element as a trigger for the signal.

If the sensor has a hermetically sealed housing, it can be used to particular advantage in work areas in which aggressive or hazardous media are used, for example in the food sector, where aggressive cleaning agents are used for cleaning purposes or in applications in which explosive media are used.

With particular advantage, the sensor according to the invention for determination of the piston position can be used on a pneumatic or hydraulic cylinder. The sensor could be fully integrated into the pneumatic or hydraulic cylinder, which greatly facilitates the handling and cleaning of such a cylinder.

Fig. 1

eine schematische Darstellung eines erfindungsgemäßen Sensors an einem Arbeitszylinder;

Fig. 2

eine schematische Darstellung eines Teils einer Energiever- sorgungseinheit des erfindungsgemäßen Sensors an einem Arbeitszylinder;

Fig.3

eine schematische Darstellung einer weiteren Ausfüh- rungsform;

Fig. 4 und 5

schematische Darstellungen weiterer Ausführungsformen.

In the following the invention with reference to an embodiment with reference to the drawings will be explained in detail. In the drawing show:

Fig. 1

a schematic representation of a sensor according to the invention on a working cylinder;

Fig. 2

a schematic representation of a portion of a power supply unit of the sensor according to the invention on a working cylinder;

Figure 3

a schematic representation of another embodiment;

4 and 5

schematic representations of further embodiments.

An in Fig. 1 illustrated working cylinder 10, which may be a pneumatic cylinder of an industrial robot, not shown, includes a piston 12 which is movable by means of a piston rod 14 in the working cylinder 10 in the longitudinal direction of the cylinder (arrow 16) within its two end positions. The piston position can be determined by means of a magnetic or inductive sensor 20, the piston 12 carrying a permanent magnet piston magnet 22 whose position the sensor 20 can detect. Such a sensor 20 is described for example in US Pat DE 10 2004 046 107 A1 ,

The sensor 20 is shown in the drawing ( Fig. 1 ) is shown only schematically and contains an inductive or magnetic sensor element 24, which responds to the magnetic field of the piston magnet 22, an evaluation unit 26, which is preferably implemented in a microcontroller and in which the signals of the sensor element 24 are further processed, and optionally necessary memory. The sensor 20 is positioned on the power cylinder 10 so that it can detect the desired piston position via the sensor element 24 or it is adapted to be electronically adjusted to certain piston positions.

According to the invention, the sensor 20 has a power supply unit 28 which is suitable for supplying the sensor 20 with electrical energy and which will be explained in more detail below. Furthermore, the sensor 20 has a transmission unit 30, by means of which signals of the sensor 20, which indicate, inter alia, the piston position, are wirelessly transmitted to a higher-level control.

In Fig. 2 next to the working cylinder 10, the essential elements of the power supply unit 28 are shown schematically. In this first exemplary embodiment, the energy supply unit 28 has an energy converter magnet 32 in the form of a permanent magnet, which is sandwiched between two piezoelements 34 and 36, for example can be glued to them. Upon movement of the piston 12, the piston magnet 22 is guided past the energy converter magnet 32, so that it experiences a force in different phases of movement in the direction of the double arrow 38 perpendicular to the stroke movement of the piston, as will be explained in more detail below. As a result, the energy converter magnet 32 exerts compressive forces in the various phases - and when the piezoelements 34 and 36 and the energy converter magnet 32 are glued together, tensile forces also act on the piezoelement 34 and the piezoelement 36. As a result, voltages are induced in the piezoelectric elements 34 and 36, which are supplied via suitable and only schematically illustrated lines 40 and 42 of a power supply electronics 44, in order ultimately to be able to supply the sensor 20 with electrical energy.

Preferably, the magnetic orientation of the piston magnet 22 in the direction of the stroke, ie in the direction of the arrow 16 and the magnetic orientation of the energy converter magnet 32 is perpendicular to the stroke. Now moves the piston 12 with its piston magnet 22 from the in Fig. 2 shown starting position to the right, the north pole of the energy converter magnet 32 is first attracted by the south pole of the piston magnet 22, so that in this phase via the energy converter magnet 32 a compressive force is exerted on the piezoelectric element 36 and this can supply an electrical voltage to the power supply electronics 44. Upon further movement of the piston 12, the north pole of the piston magnet 22 approaches the north pole of the energy converter magnet 32, and the hitherto attractive force between the two magnets turns into a repulsive force, so that in this phase of movement of the energy converter magnet 32 in the presentation of Fig. 2 will exert a force on top of the piezo element 34. As a result, a voltage is induced in the piezoelectric element 34, which in turn is dissipated to the power supply electronics 44.

In principle, it would also be possible that the effective directions of the magnets are aligned parallel or anti-parallel to each other. Thus, for example, the energy converter magnet could be oriented in the direction of the stroke, ie rotated by 90 ° in one direction or the other in relation to the illustration in FIG Fig. 2 ,

The electrical voltage and thus the energy that can be recovered is independent of the speed with which the piston 12 moves in the working cylinder 10, but is dependent on the force that the energy converter magnet 32 can exert on the piezo elements 34 and 36 , Also, this type of power generation is largely independent of the polar direction of the piston magnet 22 and the energy converter magnet 32nd

In Fig. 3 is an alternative embodiment to that of Fig. 2 shown. Here, the energy converter magnet 32 is mounted linearly movable, so that it can move freely in the direction of the double arrow 38. The storage can be realized, for example, in that the energy converter magnet 32 is held in a tube 46, which is longer than the energy converter magnet 32. Upon movement of the piston magnet 22, the energy transducer magnet 32 reacts as described above, where it can now move along its bearing in the tube 46 in the direction 38 and thus can exert only compressive forces on the piezoelectric element 34 or 36. The piezoelectric elements 34 and 36 each form stops of the displacement path of the energy converter magnet 32. In real applications, the piston 12 moves relatively quickly and accordingly the energy converter magnet 32 from a stop (piezo element 34 or 36) to the other stop (piezo element 36 or 34) shifted, due to the inertia of the energy converter magnet 32, a strong increase in the pressure at the moment of the stop on the relevant piezoelectric element. As a result, a significantly increased voltage pulse is induced in the piezoelectric element. Of course, only one piezo element can be provided at one end of the displacement path.

Combinations of arrangements of the embodiments listed separately are conceivable. Thus, for example, in the embodiment Fig. 3 the displacement and the polar direction of the energy converter magnet to be rotated by 90 °, as above too Fig. 2 executed.

The other embodiments, in the 4 and 5 are shown, the same basic principle as for the embodiment according to Fig. 2 explains, based on the fact that in each case a force is exerted on the energy converter magnet 32 via the piston magnet 22, but which is now converted in another way into a mechanical pressure force on the piezo elements.

In the embodiment according to Fig. 4 For example, the energy converter magnet 32 is disposed at one end of a lever arm 50, and the other end of the lever arm 50 is fixedly located at a point 52. As shown in FIG Fig. 3 are above and below the lever arm 50, the two piezo elements 34 and 36 are arranged so that upon exercise of a force in the direction of the double arrow 38 on the energy converter magnet 32 via the lever arm 50, either a compressive force on the piezoelectric element 34 when power is applied upward or pressure on the piezoelectric element 36 is applied via the lever arm 50 when power is applied to the energy converter magnet 32 down. In an analogous manner, as in the previous embodiment according to Fig. 2 , the voltage induced on the piezoelectric elements via the pressure is supplied to the energy supply electronics 44. Due to the leverage effect of the lever arm 50, larger forces can be exerted on the piezoelements 34 and 36 with this embodiment and thus higher voltages can be generated for the energy supply. Also, multiple energy converter magnets 32 could be placed on the lever arm 50 to further increase the force on the piezo elements 34 and 36.

In the further in Fig. 5 illustrated embodiment, only one piezoelectric element 34 is provided, that is firmly clamped at one end and at the other end 62 of the energy converter magnet 32 is arranged, which is possibly connected to the force increase via a lever arm 64 to the end 62. Now, when moving past the piston magnet 22, a force on the energy converter magnet As in the previous embodiments, the piezoelectric element 34 experiences a bending force, which in turn induces an electrical voltage which is dissipated to the energy supply electronics 44. In the drawing in Fig. 4 the bending movement of the piezoelectric element 34 is indicated by the curved shape of the double arrow 38.

Also for the other embodiments according to Fig. 3 and 4 is true that the electrical voltage and thus the energy that can be obtained, regardless of the piston speed and regardless of the polar direction of the piston magnet 22 and the energy converter magnet 32 is.

The embodiment according to Fig. 5 has the further advantage that it can be built very compact, since the sandwich-like structure is eliminated.

Since it is common in simple applications that a piston position signal is only necessary after movement of a piston, in one embodiment of the invention, the piston position signal can be triggered when the power supply unit is active, that is, an effect of the energy converter magnet on the piezoelectric element by the movement of the piston he follows. In such a case, the sensor element 24 could be omitted and the sensor 20 can be made even more cost-effective overall. However, it would then presumably be necessary to properly position the sensor 20 on the power cylinder for a switching signal to occur at the desired piston positions.

Since the sensor 20 according to the invention operates completely wirelessly, a housing of the sensor can be made hermetically sealed. It could even be completely integrated into a pneumatic or hydraulic cylinder with the exception of an antenna.

Claims (14)

Magnetic or inductive sensor for detecting a piston position along a stroke path of a piston of a working cylinder, wherein the piston carries a permanent magnet formed as a piston magnet, with an electronic evaluation unit, with which the piston position is detected and can deliver a piston position representative signal, characterized in that an energy supply unit is provided for supplying energy to the evaluation unit, which has at least one piezoelement and at least one energy converter magnet which acts on the piezoelement when the piston moves and the signal can be transmitted wirelessly from the sensor to a higher-level control. Sensor according to claim 1, characterized in that the direction of action of the energy converter magnet is perpendicular to the stroke. Sensor according to one of the preceding claims, characterized in that the magnetic orientation of the energy converter magnet is perpendicular to the stroke. Sensor according to one of the preceding claims, characterized in that the magnetic orientation of the piston magnet is in the direction of the stroke. Sensor according to one of the preceding claims, characterized in that the energy converter magnet is a permanent magnet. Sensor according to one of the preceding claims, characterized in that the energy converter magnet exerts pressure on the piezoelectric element during movement of the piston. Sensor according to claim 6, characterized in that the energy converter magnet is mounted linearly movable and upon movement of the piston magnet, the energy converter magnet is displaced along its storage and the piezoelectric element forms a stop. Sensor according to claim 6, characterized in that the energy converter magnet exerts the pressure via a lever on the piezoelectric element. Sensor according to one of the preceding claims, characterized in that the energy converter magnet exerts a bending force on the piezoelectric element during movement of the piston. Sensor according to one of the preceding claims, characterized in that a plurality of piezoelectric elements are provided and each associated with an energy converter magnet. Sensor according to one of the preceding claims, characterized in that the effect of the energy converter magnet is used on the piezoelectric element as a trigger for the signal. Sensor according to one of the preceding claims, characterized by a hermetically sealed housing. Use of a sensor according to one of the preceding claims for determination of the piston position on a pneumatic or hydraulic cylinder. Use of a sensor according to one of the preceding claims for integration into a pneumatic or hydraulic cylinder.

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