WO2016000683A1

WO2016000683A1 - Sensor for a roller conveyor and method for detecting objects located on a roller conveyor

Info

Publication number: WO2016000683A1
Application number: PCT/DE2015/100254
Authority: WO
Inventors: Oliver Prinz; Simon Kern
Original assignee: Sick Ag
Priority date: 2014-07-04
Filing date: 2015-06-23
Publication date: 2016-01-07
Also published as: DE102014109401A1; DE102014109401B4

Abstract

The invention relates to a sensor (10) for a roller conveyor (16), comprising a transmitter (22), a receiver (24), a sensor element (12), which is integrated into a roller (14) of the roller conveyor (16) or is arranged between rollers (14) of the roller conveyor (16), and an evaluating unit (26) for detecting objects located on the roller conveyor (16) on the basis of a sensor signal of the sensor element (12). The sensor element (12) has an HF filter element (13), the sensor signal is a high-frequency signal received in the receiver (24) after passing through the HF filter element (13), and the evaluating unit (26) is designed to detect the presence of objects on the basis of influences of said objects on the high-frequency signal by means of the HF filter element (13).

Description

Sensor for a roller conveyor and method for detecting objects located on a roller conveyor

The invention relates to a sensor for a roller conveyor and a method for detecting objects located on a roller conveyor according to the preamble of claims 1 and 13, respectively.

Roller conveyors are generally used as roller conveyors in storage and conveyor technology. Some of the rollers have an active drive that sets them in rotation. The remaining passive rollers can be moved along by the active rollers, or the moving objects bridge such rollers due to inertia. In order to control the material flow, the roller conveyor should be monitored for the presence of objects at certain positions of the conveyor line. For this purpose, a wide variety of sensors are known, such as optical, magnetic, inductive or capacitive sensors, which are attached to the appropriate location of the conveyor line, in order to detect the items to be conveyed on the roller conveyor.

The installation of such sensors with suitable fastening technology and wiring for connection to a power supply and a communication network, ie to a control unit or in chain to other sensors, requires considerable effort, additional space and a Einzeljustage the numerous separately mounted sensors. In addition, externally mounted sensors are in principle susceptible to mechanical impairments by the environment, such as contamination or damage to the detection surfaces. This applies in particular to optical sensors such as light barriers or light grids which observe the roller conveyor laterally or from below. The maintenance effort is thereby increased, and further, a robust housing design for mechanical protection of the sensors is necessary. Therefore, it is proposed in the prior art, such as DE 101 31 019 A1, to integrate a sensor directly in rolls of a roller conveyor. However, the technologies mentioned are only listed without details and leave serious problems unsolved. For example, the availability of optical sensors often suffers from contamination. Other principles, such as capacitive or inductive sensors, can not reliably differentiate sensor signal variations due to various extraneous influences, such as bearing clearance irregularities, temperature changes, wear or fouling, from the effects of an object on the roll. It also does not help, for example, when capacitive sensors are to hide plastic casters because it is not explained how this could be achieved. To a likewise mentioned embodiment with a radar or microwave transmitter, apart from the mention of these elements, the functional principle remains completely open. DE 20 2007 015 529 111 discloses a roller for a roller conveyor with an integrated capacitive sensor which additionally provides a reference sensor on a side remote from the conveyor side. A switching signal in an object conveyed over the roller is then determined from a difference signal between the signal of the actual sensor and the reference sensor. It is also proposed to arrange several sensors one behind the other in the longitudinal direction of the roller.

It is therefore an object of the invention to enable a reliable presence detection of objects on a roller conveyor. This object is achieved by a sensor for a roller conveyor and a method for detecting objects located on a roller conveyor according to claim 1 or 13. The sensor element of the sensor is integrated into a roller of the roller track or preferably arranged parallel to it between the rollers. The invention is based on the basic idea of having a high-frequency signal (HF signal) passed through a high-frequency filter element (HF filter element). Objects in the vicinity of the RF filter element affect the high-frequency signal, and this effect is used in the evaluation of the received high-frequency signal for detecting the presence of the objects. The invention has the advantage that by integration into the roller conveyor or even into a roller only a minimal installation effort without additional space required allows becomes light, at the same time the sensor is protected from external influences. The sensor is simple in design and requires only a minimum of measuring effort. Unlike optical sensors, the sensor based on high-frequency signals is insensitive to dust and contamination. This enables particularly robust, reliable and simple presence detection for objects on a roller conveyor.

The sensor is preferably integrated in a roller or in a frame of the roller conveyor. This not only integrates the RF filter element, but also integrates the other elements of the sensor, such as transmitter, receiver and evaluation unit. The most compact is a system integrated into the roll. But even when integrated into a frame of the roller conveyor additional, exposed elements are avoided and reduced space requirements. There is only one connection line for the supply and the data connection required. Even this connection cable can still be avoided by wireless communication such as radio or wireless or autonomous supply.

The RF filter element is preferably designed as a single-circuit or as a multi-circuit and, in a development of the invention, has at least one resonant structure in or on the surface of the sensor element. The resonant structure preferably extends over at least a large part or even the full length of the sensor element for a large detection range. In the radial direction, the resonant structure is aligned at an interposed between the rollers, not co-rotating sensor element up to the possible objects. If the resonant structure is part of a role, co-rotation can result in the role of even presence detection being periodically obstructed. This can be acceptable depending on the roll size, sensitivity of the sensor and object sizes.

It is furthermore conceivable to provide a plurality of resonant structures distributed over the longitudinal extent and / or the circumference of the sensor element and to interconnect in total or in groups in parallel or in series. Several parallel branches can then be evaluated individually, with the results being summarized later, ie algorithmically, or the high-frequency signal is distributed to a splitter or combiner on the transmitting side of the plurality of resonant structures and combined at the receiving end. This combination preferably does not take place via all resonant structures, but only via groups in a common radial direction, because each in the course of the rotational movement of the roller facing away from the objects resonant structures hardly contribute meaningful measurement information. The resonant structure is preferably produced by microstrip technology or coplanar technology. For example, a thin metallic layer is applied to a plastic film or vapor-deposited.

In a development of the invention, the HF filter element can have at least one resonant structure in the interior of the sensor element. In principle, structures in a technique come into question, as they can also be used on the surface. On the other hand, there is no need to be so limited in the thickness of the structure. In any case, it must be ensured that an interaction with an object can occur, for example, by opening in a metallic shell around the inner resonant structure, or entirely without a metallic shell.

As already mentioned, the RF filter element can be designed to be multi-circuited and have a plurality of resonant structures of different resonant frequency. This can be a possibility to build up RF filter elements of higher order from several resonant structures.

The resonant structure may comprise a cavity resonator in a further development of the invention. Here, the resonance of the electromagnetic field does not arise on an external particular resonant structure, but within a cavity. Particularly preferably, the roller itself is the cavity resonator. This is possible with a metallic shell and makes the role also particularly resistant and durable. The cavity resonator preferably has openings over its longitudinal extension and / or circumference. Through these openings, which for example have the shape of slots or other geometries, the field can emerge from the interior of the cavity resonator. This evanescent field interacts with a present object. With regard to the distribution of openings over the longitudinal extent and the circumference of the sensor element, the above statements apply correspondingly to the distribution of resonant structures, that is to say that the formation is so must be able to interact with an object conveyed over the rollers, ie the object sufficiently influences the RF signal in the RF filter element. The cavity resonator may include a dielectric fill for adjusting the resonant frequency. The dielectric filling may be formed continuously or with defects or cavities and different materials. The openings to the field exit or other elements such as apertures, tuning screws and other waveguide components can be used to adjust the resonant frequency.

The RF filter element may also comprise a dielectric resonator. As such a dielectric resonator, the sensor element has a structure without metallic sheath or structures on the outside which could be abraded. Particularly preferably, the roller itself is designed as the rod-shaped dielectric. Inside the dielectric, a cavity may be provided.

The evaluation unit is preferably designed to excite the RF filter element with the high-frequency signal at approximately the resonant frequency of the resonant structure. Thus, a change by a present object is detected particularly sensitive. An excitation at several frequency points or with continuously changed frequency is alternatively conceivable.

The evaluation unit is particularly preferably designed to evaluate the filter curve, the quality of the resonance, a detuning of the filter or an impedance of the resonator element in order to detect the presence of objects. The quality of the resonance decreases with a well adjusted resonant structure by the present object. This is measured, for example, by the half-width of the resonance peak. In addition, the resonant frequency is detuned, that is, it is shifted to a different frequency than the situation without objects. The tuned resonant frequency can be determined, or it can be determined that the system is no longer responding to the now detuned excitation frequency as much as before. Furthermore, the impedance in resonance is purely real. The detuning by the object generates an inductive or capacitive component, at which the presence of the object can be detected. The evaluation unit is preferably designed to determine in advance a calibration signal in the absence of objects and then to consider them for the detection of objects. Thus, in a kind of empty calibration those influences on the high frequency signal are detected, which are not caused by an object to be detected. They are then taken into account in operation in a simple manner by subtracting the calibration signal from the respective received high-frequency signal. This procedure implies a reference comparison. If significant differences to zero remain after subtracting the calibration signal, it is possible to deduce the presence of an object.

The evaluation unit is even more preferably designed to determine or adjust the calibration signal during operation on the basis of a history of high-frequency signals. Here, therefore, the empty calibration without an object is not only initial, but dynamic. Ultimately, it is preferably a filter with Tiefpasseigen- create, that forgets fast changes by objects and far past influences on the high-frequency signal. The filter parameters should be set so that slow-moving objects or objects in the temporary jam yet trigger no adjustment, but only long-term effects such as deposits on the roll. An initial empty calibration can be a factor in the design of the filter.

In an advantageous embodiment, a roller is provided with a sensor according to the invention integrated therein. This role may have its own drive, so be an active role. Then, the sensor preferably uses the supply and control lines of this drive. The sensor can also be used in a passive role without its own drive. Then the sensor requires its own connections or supplies itself and communicates wirelessly. It is also conceivable to equip the sensor with a battery or its own power generation from the rotational movement.

The inventive method can be configured in a similar manner by further features and shows similar advantages. Such further features are exemplary, but not exhaustive, in which subclaims following the independent claims are described. The invention will be explained below with regard to further advantages and features with reference to the accompanying drawings with reference to embodiments. The figures of the drawing show in: Fig. 1 is a plan view of a roller conveyor with an integrated into a roll

Sensor for presence detection of objects on the roller conveyor; Figure 2 is a plan view of a roller conveyor with a sensor for detecting the presence of objects, the sensor element is arranged between the rollers.

3 is a block diagram of a sensor with a cavity resonator;

4 shows a block diagram of a sensor with a resonant structure on the surface;

5 is a block diagram of another sensor with a different resonant structure on the surface;

6 and 7 are block diagrams of alternative embodiments of a sensor with an RF filter element.

Figure 1 shows a plan view of a sensor 10, the sensor element 12 is integrated in a roller 14 of a roller conveyor 16. The rollers 14 rotate actively or passively by co-movement with an object, not shown, which moves along the roller conveyor 16. The sensor 10 has a sensor head 18, the elements of which will be explained in more detail below with reference to FIG. Various embodiments of the sensor element 12 in turn will be explained with reference to FIGS 3-6. In the embodiment according to FIG. 1, the sensor head 18 is integrated in a frame 20 of the roller track 16. In other embodiments, the sensor head 18 is also incorporated in the roller 14.

FIG. 2 shows a plan view of an alternative arrangement, where the sensor element 12 is a separate component, which is arranged between the rollers 14, in particular parallel thereto. In its structure, the separate sensor element 12 may resemble a roller 14, so also be made as a circular cylinder and made of the same materials. However, the separate sensor element 12 does not necessarily rotate with, but may also be rotatably mounted in the frame 20 and have a different diameter than a roller 14th

FIG. 3 shows a block diagram of the sensor 10. The sensor head 18 has a transmitter 22, a receiver 24 and an associated control and evaluation unit. processing unit 26. Transmitter 22 and receiver 24 generate and receive a radio frequency (RF) signal. The coupling to the sensor element 12 takes place, for example, capacitively or directly through a connector. The sensor element 12 is here and in all subsequent representations alternatively integrated into the roller 14 as in FIG. 1 or a separate component as in FIG. 2.

All embodiments have in common that the sensor element 12 has a high-frequency filter element (RF filter element) 13, which has resonant structures in the various exemplary embodiments (FIGS. 3 to 7).

In the embodiment according to FIG. 3, the HF filter element 13 is designed as a cavity resonator 28. Cavity resonators are structures with metallically sealed walls, in which a standing wave is caused by electromagnetic oscillations. The natural frequency of the resonator results as a solution of Maxwell's equations taking into account the boundary conditions. These are essentially the geometric dimensions and materials used. In principle, the solution of the equations leads, due to the infinite number of possible modes or field distributions, to a multiplicity of resonance frequencies. If one considers that a real resonator is a lossy system with decaying vibration behavior, energy must be supplied to the system. Here can be specifically stimulated by appropriate frequency and excitation a mode.

The cavity resonator 28 has openings 30, in particular slots, through which the field evanescently engages in the space outside of the cavity 28 and is influenced there, provided that an object is in the area of the field. In this case, unlike a slot antenna, no radiation takes place. The presence of an object in the region of the openings 30 influences the evanescent field and thus detunes the cavity resonator 28, that is to say it changes its frequency and / or quality. This effect is used by the evaluation unit 26 for the detection of objects on the roller conveyor 16. The number, geometry and arrangement of the openings 30 are designed so that the presence of objects is detected as reliably as possible. Depending on whether the sensor element 12 rotates or not, openings 30 on the upper side or, preferably, openings 30 over the entire circumference should be distributed. Through the openings 30 and conceivable further elements such as diaphragms, tuning screws, dielectric fillings and / or further waveguide a suitable cavity resonator can be designed, in particular an already existing roller 14 of the roller conveyor 16 also act directly as a cavity resonator 28. Instead of the cavity resonator 28, it is also possible to use a dielectric resonator (not shown), that is to say a sensor element 12 made of a dielectric which is not metallically coated on the outside. Typically, a dielectric with a high dielectric constant compared to the surrounding air should be selected, but the material should also withstand the stresses as a roller 14, at least in one embodiment according to FIG.

In contrast to the cavity resonator 28, in which the fields are usually bounded by metal walls, in the dielectric resonator, the evanescent fields reach outward. The entire HF filter element, that is to say here the entire sensor element and in particular the entire roller 14, can act as a dielectric resonator. Much of the energy is held in the dielectric with its dielectric constant greater than one 1. At the air surface, an evanescent field is formed. By suitable choice of the dielectric, design of the sensor element 12 as a tube or solid roller and possible further resonance-tuning elements, the influence of an object can be used to detune the dielectric resonator and ensure reliable detection on the roller conveyor 16 , Incidentally, a mixed form of a metallic resonator filled with a dielectric is also conceivable. FIG. 4 shows an alternative embodiment with a sensor element 12, in which the filter element 13, instead of a cavity resonator 28, has a resonant structure 32 on its surface. The special geometry of the resonant structure 32 is to be understood purely by way of example. As in all embodiments, the detection ability improves when the largest possible field component in the air is guided in the vicinity of the sensor element 12 in order to be influenced by the objects located on the roller conveyor 16 and thus to provide a measurement signal. This desired field distribution thus also represents an optimization criterion for the design of the resonant structure 32. Together with the selected frequency, the sensitivity to interference influences can thus be influenced. The resonant structure 32 is implemented, for example, in microstrip technology or coplanar technology. The electromagnetic fields of the resonant structure 32 are largely conducted in the substrate, only a small field share attacks in the air. An air-deviating dielectric constant of a present object influences the evanescent field and leads to a detuning of the resonator, since the resonance condition changes. This effect can be used for detection as long as the object differs in its dielectric constant from air.

For an improved and at least roughly spatially resolved detection, a plurality of resonant structures 32 or oscillating circuits can be distributed over the surface of the sensor element 12 and connected in total or in groups in parallel or series connection. The RF filter element 13 is then formed mehrkreisig. Connection and evaluation are carried out individually, in groups or jointly by transmitting-side separation and reception-side merging of some or all high-frequency signals by means of coupler elements (power splitter, power combiner).

For the evaluation of a resonator, regardless of which embodiment, the following three measured variables, resonance frequency, quality and impedance, among others, can be used.

The resonator is designed in each case to a specific resonance frequency. The presence of an object detunes the resonator. An evaluation of the frequency and / or phase allows the determination of the frequency shift. If there is a shift in the resonance frequency compared to a measured reference, then it is possible to conclude an object.

The parameter of the quality can also be used, for example, by measuring the width of the resonance curve. Again, this could be compared to a reference curve or a reference width. In the case of broadening or deviating from the reference curve, the object presence can be deduced.

If the resonator is operated at its resonant frequency, it also has a purely real impedance (XL + XC = 0). Depending on the type (parallel or series resonance), the real impedance component becomes minimum or maximum. Through a present object the resonator is detuned so that the impedance gets an inductive and / or capacitive component, which can be evaluated.

For all these evaluations, a threshold evaluation is possible with the triggering of a switching signal in the presence of objects.

Figures 5 to 7 show a further embodiment of the RF filter element 13, which may have, for example, high, low or bandpass or other properties. For this purpose, a filter structure 34 is provided on the surface of the sensor element which, in principle, has a similar structure as the resonant structure 32, but is not designed for a specific resonant frequency but for a filter characteristic.

The filter structure 34 may also be located inside the sensor element 12 instead of on the surface, e.g. in a dielectric, in a cavity of a dielectric with or without a metallic shell or in a cavity with a metallic shell. If a metallic shell is provided, however, it must be ensured that the electromagnetic field can penetrate to the outside, for example through suitable openings, since an interaction with the object should take place. The outside view of FIGS. 5 to 7 can then be considered practically as a sectional view. The possibility of arrangement in an interior also applies to the resonant structure 32 according to FIG. 4.

In FIGS. 5 to 7, furthermore, the sensor head 18 is integrated into the roller 14, and the high-frequency signal is no longer received in reflection, but in transmission. This illustrates once again that most of the variations of the arrangement of the sensor element 12, of the RF filter element 13 and of the elements of the sensor head 18 shown in various figures can be combined in great variation. With a filter structure 34, the resonance of a metallic structure is utilized. The commensurated RF filter element 13 according to FIG. 5, for example, works with stubs which are either short-circuited or operated in the open end. This achieves a resonance line. With the combination of several stubs, which have similar resonant frequencies, the filter characteristic of a certain order is achieved. The lengths of the stubs as well as the connecting lines are chosen in the design approach to λ / 4. Overall, the filter structure 34 shown in FIG. 5 acts as a low pass. FIG. 6 shows an example of a filter structure 34 which acts as a bandpass, and FIG. 7 shows a finger filter. The respective filter characteristics are optimized by computer-aided models. On the one hand, the goal of optimization is the greatest possible interaction with the objects present. In addition, the filter type should be optimized so that the filter structure 34 can be mounted over a large area on the sensor element 12 or a roller 14. Often, the distribution of multiple filter structures 34 over the full extent and the entire longitudinal extent makes sense. These filter structures 34 are interconnected and evaluated individually, in groups or jointly as described above for a plurality of resonant structures 32. Particularly suitable as a filter is a Coupled Line Bandpass, since here the influence of materials with a dielectric constant differing from air over the entire filter length is similar. The series connection of filters makes it possible to detect the presence of an object independently of the location, as this shifts the entire filter curve.

The principle of operation of a filter structure 34 is that electromagnetic energy in a filter that is realized on a substrate is partly guided in the substrate and partly also the field reaches into the air, since the filter is not shielded. The change in the dielectric constant on the side where the field strikes the air leads to detuning of the filter as resonance conditions change. This effect is used for object detection.

The evaluation takes place in reflection or transmission, in that the amplitude and phase are evaluated at several frequency points or continuously. This is compared to stored reference curves. Deviation from the reference makes it possible to deduce the presence of an object. When evaluating several frequency points, a shift of the filter curve is directly visible. Optionally, the evaluation of a signal delay time is possible with an amplitude, frequency or phase modulation of the input signal, which can be closed to the position of the object.

Finally, it is again pointed out that the features shown in the figures can also be combined differently. Thus, not only is it possible in each case to integrate the sensor element 12 into the roller 14 or to arrange it between rollers 14 or to arrange each transmitter 22 and receiver 24 in reflection or transmission. Combinations of measuring principles are also conceivable, ie sensors 10 with different resonator elements presented here, but also additional rollers or sensor elements between rollers which are based on completely different physical principles such as optical or capacitive detection.

Claims

Sensor (10) for a roller conveyor (16) with a transmitter (22), a receiver (24) and a sensor element (12) integrated in a roller (14) of the roller conveyor (16) or between rollers (14) of the roller conveyor (16) is arranged, and with an evaluation unit (26) for detecting objects located on the roller conveyor (16) based on a sensor signal of the sensor element (12), characterized

in that the sensor element (12) has an HF filter element (13),

- That the sensor signal is a after passing through the RF filter element (13) in the receiver (24) received high-frequency signal and

- That the evaluation unit (26) is adapted to detect the presence of objects based on their influence of the high-frequency signal through the RF filter element (13).

Sensor (10) according to claim 1,

wherein the sensor (10) is integrated in a roller (14) or in a frame (20) of the roller conveyor (16).

Sensor (10) according to claim 1 or 2,

wherein the RF filter element (13) is single-circuit or multi-circuit and has at least one resonant structure (32, 34) on the surface and / or in the interior of the sensor element (12).

Sensor (10) according to claim 3,

wherein the resonant structure (32, 34) on the surface is made by microstrip technology or coplanar technique.

Sensor (10) according to one of the preceding claims 3 to 4,

wherein the RF filter element (13) has a plurality of resonant structures with different resonance frequencies.

6. Sensor (10) according to one of the preceding claims 3 to 5,

wherein the RF filter element (13) has a cavity resonator (28) and in particular the roller (14) forms the cavity resonator (28).

7. Sensor (10) according to claim 6,

wherein the cavity resonator (28) has openings (30) over its longitudinal extension and / or circumference.

Sensor (10) according to claim 6 or 7,

wherein the cavity resonator (28) has a dielectric fill for adjusting the resonant frequency.

Sensor (10) according to claim 3,

wherein the resonant structure comprises a dielectric resonator, in particular the roller (14) is designed as a dielectric resonator.

10. Sensor (10) according to one of the preceding claims 3 to 8,

wherein the evaluation unit (26) is adapted to excite the RF filter element (13) with a high frequency signal at approximately one resonant frequency of the resonant structure (28, 32, 34) and / or the quality of the resonance, a detuning of the resonant frequency or an impedance of the resonant structure (28, 32, 34) to detect the presence of objects.

11. Sensor (10) according to one of the preceding claims,

wherein the evaluation unit (26) is adapted to determine in advance a calibration signal in the absence of objects and then to take into account for the detection of objects and in particular to determine or adjust the calibration signal in operation on the basis of a history of high-frequency signals.

Roller (14) with a sensor (10) according to one of the preceding claims.

Method for detecting objects located on a roller conveyor (16) by evaluating a sensor signal of a sensor element (12) integrated in a roller (14) of the roller conveyor (16) or between rollers (14) of the roller conveyor (16)

characterized,

in that a high-frequency signal is fed as sensor signal into an HF filter element (13) of the sensor element (12) and after passing through the HF filter element (13) is received and evaluated to detect the presence of objects based on influences of the high-frequency signal by the RF filter element (13).