DE102014109401B4 - Sensor for a roller conveyor and method for detecting objects located on a roller conveyor - Google Patents

Abstract

Sensor (10) for a roller conveyor (16) with a transmitter (22), a receiver (24) and a sensor element (12), which is integrated in a roller (14) of the roller conveyor (16), and with an evaluation unit (26 ) for detecting objects located on the roller conveyor (16) on the basis of a sensor signal of the sensor element (12), characterized in that the sensor element (12) has an RF filter element (13) which is designed as - several over the circumference of the sensor element (12) distributed resonant structures (32, 34), - a cavity resonator (28) with openings distributed over the circumference of the sensor element (12) or - a rod-shaped dielectric resonator that transmits the sensor signal from the transmitter (22) and after passing through the RF filter element (13) is in the receiver (24) received high-frequency signal and that the evaluation unit (26) is adapted to detect the presence of objects, that in the vicinity of the RF filter element (13 ) objects affect the current through the RF filter element (13) high-frequency signal.

Description

The invention relates to a sensor for a roller conveyor and to 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 other passive rollers can be moved by belts from the active wheels, 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 variety of sensors are known, such as optical, magnetic, inductive or capacitive sensors, which are attached to the appropriate location of the conveyor line to detect the 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 single adjustment of 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, in the prior art, about the DE 101 31 019 A1 , proposed 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.

The DE 20 2007 015 529 U1 discloses a roller for a roller conveyor with an integrated capacitive sensor, which additionally provides on a side facing away from the conveying side, a reference sensor. 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 a plurality of sensors in the longitudinal direction of the roller one behind the other.

From the US 4,868,488 A It is known to guide a high frequency signal via waveguide to a microwave resonator and to receive it again. This arrangement functions by evaluating the high-frequency signal as a sensor for determining the relative position between the microwave resonator and a body. A presence detection on a roller conveyor is not provided.

The DE 10 2005 039 851 A1 describes a humidity sensor based on the principle that a water droplet causes a resonance shift in a resonant structure of the sensor.

The WO 00/04 375 A1 deals with the determination of material properties by evanescent microwaves generated by a microstrip resonator.

In the US 4,475,089 A a proximity sensor is disclosed, which has a metallic hollow chamber as a resonator.

The DE 198 07 593 A1 describes a distance measuring device with a sensor and an evaluation, wherein the sensor comprises a resonator in the form of a cavity resonator.

From the DE 23 54 151 A1 For example, an absorption waveguide filter of rectangular cross-section is known which has a number of spaced-apart slots in one wide wall.

The WO 00/28 615 A1 discloses a dielectric waveguide for a sensor for detecting material properties, which is used as a microwave resonator.

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 Claim 1 or 13 solved. The sensor element of the sensor is integrated into a roller of the roller conveyor. 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 only a minimum of assembly work without additional space requirement is made possible by integration in the role, in which 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.

Not only the RF filter element, but also the other elements of the sensor are preferably integrated in the roller or in a frame of the roller conveyor, 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 formed in a single-circuit or multi-circuit and, in a further 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 the resonant structures, but only via groups in a common radial direction, because the respective resonant structures facing away from the objects in the course of the rotational movement of the roller 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 it can interact with an object by, for example, openings are placed in a metallic shell around the inner resonant structure or is completely dispensed with 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 to Corresponding distribution of resonant structures, ie, that the training must be such that it can come to an interaction with an object conveyed over the rollers, so that the object sufficiently affects 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 for field exit or other elements such as diaphragms, 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 resonance frequency is detuned, so compared to the situation without objects moved to a different frequency. 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 radio-frequency signal. This procedure implies a reference comparison. If, after subtracting the calibration signal, there are significant differences to zero, then the presence of an object can be deduced.

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 low-pass characteristics, which therefore 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:

1 a plan view of a roller conveyor with a built-in roll sensor for detecting the presence of objects on the roller conveyor;

2 a plan view of a roller conveyor with a sensor for presence detection of Objects whose sensor element is arranged between the rollers;

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

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

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

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

1 shows a plan view of a sensor 10 , its sensor element 12 in a role 14 a roller conveyor 16 is integrated. The roles 14 rotate actively or passively by co-movement with an object, not shown, extending along the roller conveyor 16 emotional. The sensor 10 has a sensor head 18 whose elements are described below on the basis of 3 be explained in more detail. Various embodiments of the sensor element 12 in turn, will be based on the 3 - 6 explained. The sensor head 18 is in the embodiment according to 1 in a frame 20 the roller conveyor 16 integrated. In other embodiments, the sensor head is 18 also in the role 14 built-in.

2 shows a plan view of an alternative arrangement, where the sensor element 12 a separate component is that between the rollers 14 is arranged in particular parallel to it. In its construction, the separate sensor element 12 a role 14 similar, so also be made as a circular cylinder and made of the same materials. The separate sensor element 12 but not necessarily with, but can also rotatably in the frame 20 be stored and have a different diameter than a roll 14 ,

3 shows a block diagram of the sensor 10 , The sensor head 18 has a transmitter 22 , a receiver 24 as well as a related control and evaluation unit 26 on. transmitter 22 and receiver 24 generate or receive a high-frequency signal (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 following representations alternatively in the role 14 integrated as in 1 or a separate component as in 2 ,

All embodiments have in common that the sensor element 12 a high frequency filter element (RF filter element) 13 having resonant structures in the various embodiments ( 3 to 7 ).

In the embodiment according to 3 is the RF filter element 13 as a cavity resonator 28 educated. 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 on, in particular slots, through which the field evanescently into the space outside the cavity resonator 28 engages and is influenced there, if an object is in the area of the field. In this case, unlike a slot antenna, no radiation takes place. Due to presence of an object is in the area of the openings 30 the evanescent field and thus the cavity resonator are affected 28 detuned, so its frequency and / or quality changed. This effect is provided by the evaluation unit 26 for the detection of objects on the roller conveyor 16 used. 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 rotated or not, openings are sufficient 30 at the top or should preferably have openings 30 distributed over the entire circumference. Through the openings 30 and conceivable further elements, such as diaphragms, tuning screws, dielectric fillings and / or further waveguide components, a suitable cavity resonator can be designed, in particular an already existing roller 14 the roller conveyor 16 directly as a cavity resonator 28 act.

Instead of the cavity resonator 28 It is also possible to use an unrepresented dielectric resonator, that is to say a sensor element 12 made of a dielectric that is not metallically coated on the outside. Typically, a dielectric should be chosen with respect to the surrounding high-dielectric-constant air, but in at least one embodiment according to 1 also the stresses as role 14 should withstand.

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 RF filter element, so here the entire sensor element and in particular the entire role 14 can act as a dielectric resonator. Much of the energy is kept in the dielectric with its dielectric constant greater than one. 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 reliable detection on the roller conveyor 16 to ensure. Incidentally, a mixed form of a metallic resonator filled with a dielectric is also conceivable.

4 shows an alternative embodiment with a sensor element 12 in which the filter element 13 instead of a cavity resonator 28 a resonant structure 32 on its surface. The special geometry of the resonant structure 32 is purely exemplary to understand. As in all embodiments, the detection capability improves when the largest possible field share in the air in the vicinity of the sensor element 12 is led to by the on the roller conveyor 16 to be influenced objects 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 can thus be influenced.

The resonant structure 32 is carried out, for example, in microstrip technology or coplanar technology. The electromagnetic fields of the resonant structure 32 are mostly led in the substrate, only a small field share attacks in the air. A non-air dielectric constant of a present object affects the evanescent field and causes detuning of the resonator as 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 multiple resonant structures 32 or resonant circuits over the surface of the sensor element 12 distributed 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. When widening 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. By 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.

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

The filter structure 34 can also take place on the surface inside the sensor element 12 are located, for. Example, 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 exterior view of the 5 to 7 can then be understood in practice as a sectional view. The possibility of arrangement in an interior also applies to the resonant structure 32 according to 4 ,

In the 5 to 7 is also the sensor head 18 in the role 14 integrated, and the high-frequency signal is no longer received in reflection, but in transmission. This again illustrates that most of the variations shown in various figures are the arrangement of the sensor element 12 , the RF filter element 13 and the elements of the sensor head 18 can be combined in a large variation.

With a filter structure 34 the resonance of a metallic structure is exploited. The RF filter element 13 according to 5 For example, it works with stubs that are either shorted or open ended. 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 in 5 shown filter structure 34 as a low pass. 6 shows an example of a filter structure 34 , which acts as a bandpass, and 7 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 large area on the sensor element 12 or a role 14 can be attached. Also common is the distribution of multiple filter structures 34 meaningful over the full circumference and the entire longitudinal extent. These filter structures 34 be similar to above for several resonant structures 32 described individually, in groups or jointly interconnected and evaluated. Particularly suitable as a filter is a bandpass filter made of coupled lines (Coupled Line Bandpass), since here the influence of materials with a dielectric constant differing from air over the entire filter length is similar. By connecting filters in series, the presence of an object can be detected independently of the location, as this shifts the entire filter curve.

The principle of operation of a filter structure 34 is that electromagnetic energy is realized in a filter, which is realized on a substrate, partly in the substrate and partly engages the field in 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 is carried out in reflection or transmission by the amplitude and phase is 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. So not only is it possible in each case, the sensor element 12 in the role 14 to integrate or between roles 14 to arrange or each transmitter 22 and receiver 24 to arrange in reflection or transmission.

There are also conceivable combinations of measuring principles, ie sensors 10 with various resonator elements presented here, but also additional rollers or sensor elements between rollers based on quite different physical principles such as optical or capacitive detection.

Claims (13)

Sensor ( 10 ) for a roller conveyor ( 16 ) with a transmitter ( 22 ), a recipient ( 24 ) and a sensor element ( 12 ), which is in a role ( 14 ) of the roller conveyor ( 16 ) and with an evaluation unit ( 26 ) for detecting on the roller conveyor ( 16 ) based on a sensor signal of the sensor element ( 12 ), characterized in that the sensor element ( 12 ) an RF filter element ( 13 ) which is configured as - a plurality over the circumference of the sensor element ( 12 ) distributed resonant structures ( 32 . 34 ), - a cavity resonator ( 28 ) with over the circumference of the sensor element ( 12 ) or a rod-shaped dielectric resonator, that the sensor signal from the transmitter ( 22 ) and 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 by the fact that in the vicinity of the RF filter element ( 13 ) located by the RF filter element ( 13 ) influence running high-frequency signal. Sensor ( 10 ) according to claim 1, wherein further elements ( 22 . 24 . 26 ) of the sensor ( 10 ) in the role ( 14 ) or in a frame ( 20 ) of the roller conveyor ( 16 ) are integrated. Sensor ( 10 ) according to claim 1 or 2, wherein the RF filter element ( 13 ) is formed in a single or multiple circuit and at least one resonant structure ( 32 . 34 ) on the surface and / or inside the sensor element ( 12 ) having. Sensor ( 10 ) according to claim 3, wherein the resonant structure ( 32 . 34 ) is produced on the surface in microstrip technology or Koplanartechnik. Sensor ( 10 ) according to one of claims 3 or 4, wherein the RF filter element ( 13 ) has a plurality of resonant structures with different resonance frequencies. Sensor ( 10 ) according to one of claims 1 or 2, wherein the roll ( 14 ) the cavity resonator ( 28 ). Sensor ( 10 ) according to claim 6, wherein the cavity resonator ( 28 ) over its longitudinal openings ( 30 ) having. Sensor ( 10 ) according to claim 6 or 7, wherein the cavity resonator ( 28 ) has a dielectric filling for adjusting the resonant frequency. Sensor ( 10 ) according to claim 3, wherein the roll ( 14 ) is formed as a dielectric resonator. Sensor ( 10 ) according to one of the preceding claims, wherein the evaluation unit ( 26 ) is adapted to the RF filter element ( 13 ) with a high-frequency signal having 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. 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 be considered for the detection of objects. Roll ( 14 ) for a roller conveyor ( 16 ) with one in the role ( 14 ) integrated sensor ( 10 ) according to any one of the preceding claims. Method for detecting on a roller conveyor ( 16 ) by evaluating a sensor signal of a sensor element ( 12 ), which is in a role ( 14 ) of the roller conveyor ( 16 ) is integrated, characterized in that as a sensor signal, a high-frequency signal in an RF filter element ( 13 ) of the sensor element ( 12 ) and after passing through the RF filter element ( 13 ) is received and evaluated to detect the presence of objects due to the fact that in the vicinity of the RF filter element ( 13 ) located by the RF filter element ( 13 ) influence current high-frequency signal, wherein the RF filter element is designed as - several over the circumference of the sensor element ( 12 ) distributed resonant structures ( 32 . 34 ), - a cavity resonator ( 28 ) with over the circumference of the sensor element ( 12 ) or a rod-shaped dielectric resonator.

Images