Method and device for positioning workpieces

Abstract

For positioning workpieces (2) on a conveying means (3), the position of the workpiece (2) which is moved by the conveying means (3) is detected with the aid of markings (11) allocated to the conveying means (3). To this end, the number of markings (11) allocated to the conveying means (3) which have moved past at least one stationary reading head (10) is detected. In particular, markings (11) provided on a measuring tape (9) connected to the conveying means (3) are used.

Description

[0001]METHOD AND DEVICE FOR POSITIONING WORKPIECES The invention relates to a method for positioning workpieces on a conveyor and to a device with which the method can be carried out. In the prior art, the precise positioning of workpieces, in particular glass panes or insulating glass blanks, is a problem that often has to be solved so that the workpiece is in the right place for processing. For this purpose, it is known to move workpieces standing on a conveyor (for example a toothed belt), with the position being detected by a servo drive motor. If stiff and precise toothed belts are used, the position of the workpiece can be detected via backlash-free toothing with the help of toothed belt pulleys and low-backlash gears. In addition, the position of workpieces on a deflection roller over which an endless conveyor is guided can be detected.The aim is to keep the influence of stretching of the conveyor (e.g. a toothed belt) and similar devices as low as possible. It is also known to attach an auxiliary drive, for example via a suction cup, to the workpiece to be transported and positioned, operated by rack and pinion or ball screw drives. The problem with known conveyor systems using belts and / or bands is that these stretch to a greater or lesser extent when subjected to load, for example due to the weight of the workpiece. Due to this stretching of the conveyor, a workpiece standing or lying on the conveyor cannot be positioned precisely. This is particularly problematic when back and forth movements are required when positioning the workpiece, which is particularly problematic with heavy workpieces and leads to inaccurate positioning of the workpiece.Finally, manufacturing tolerances in conveying devices such as conveyor belts lead to inaccurate positioning of workpieces. Conveying devices with conveyor elements in the form of conveyor belts, which are used to transport glass panes or insulating glass blanks, are known from AT 515212 B1 or EP 3433 576 B1. However, these known conveying devices do not solve the problem described above. The prior art has also included proposals for determining the elongation of conveying devices with conveyor belts as the conveying element. For example, reference is made to WO 2022 / 199760 A1 and WO 2022 / 156848 A1. DE 4120 216 A1 discloses a method for determining the workpiece position in a conveyor belt furnace. In this method, workpieces are placed on a conveyor belt in a loading position before entering a furnace chamber, are moved continuously or discontinuously through the furnace chamber on the conveyor belt, and are removed from the conveyor belt after leaving the furnace chamber.Marking points are provided on the conveyor belt. The distance between the drop-in point of a workpiece and a neighboring mark-in point is detected by scanning with a stationary sensor, and the distance traveled by the mark-in point during advance of the conveyor belt is determined. The position of the workpiece is then determined from the distance traveled by the mark-in point and from the distance between the mark-in point and the drop-in point of the workpiece. EP 3896 013 A1 describes a position information processing device for a conveyor belt, wherein the device comprises a plurality of magnet rows arranged at spaced-apart positions in a circumferential direction within or on a surface of the belt body of the conveyor belt.Each magnet row contains a plurality of magnets, wherein each of the plurality of magnet rows forms a pole arrangement, and the plurality of magnet rows differ from one another in the pole arrangement. The position information is provided by an arrangement of the respective poles of the plurality of magnets. The known device further comprises a magnetic sensor unit and a processing unit. The magnetic sensor unit is configured to detect the respective poles of the plurality of magnets, which are then processed into a position in the processing unit. EP 0753 472 A1 discloses a method for inductively monitoring a conveyor belt with electrical transmitters made of integrated circuit transponders inserted at intervals from one another and with at least one transmitting and receiving device arranged stationary outside the belt.The invention is based on the object of proposing a method and a device with which workpieces that are transported and moved on a conveyor are detected precisely and accurately. This object is achieved on the one hand with a method that uses the features of the independent claim directed to the method, and on the other hand with a device that has the features of the independent claim directed to the device. Because, in the invention, markings are assigned to the conveyor and the markings are detected by at least one stationary read head, it is possible to determine the exact position of the workpiece on the conveyor based on the number of markings detected by the read head. The method according to the invention can be applied to conveyors that have an endless conveyor link or a finite conveyor link.Examples of conveyors include conveyor belts, flat belts, toothed belts, V-belts, and chains. In a practical embodiment of the invention, a measuring tape connected to the conveyor, on which the markings are provided, can be used. This measuring tape is preferably a longitudinally elastic measuring tape that can stretch along with the conveyor. Within the scope of the invention, it is possible and preferred to detect changes in the distance between markings provided on the conveyor or on the measuring tape connected to the conveyor and to take them into account when determining the position of the workpiece being transported and positioned on the conveyor.It is preferred that changes of varying magnitude in the distance between consecutive markings be weighted, with it being preferred that changes in the distance between consecutive markings in the region of the center of gravity of the transported workpiece be emphasized ("weighted") during weighting. This takes into account the fact that expansions of the conveyor—and thus changes in the distance between consecutive markings—predominantly occur in the region of the center of gravity of workpieces transported on the conveyor. When carrying out the method according to the invention, the starting position of the workpiece on the conveyor can be detected precisely and without play using a sensor assigned to the conveyor.In this case, it is preferably carried out in such a way that, after the starting position of the workpiece has been detected by the sensor, the positioning of the workpiece is carried out with the aid of the markings provided, for example, on the measuring tape, and the reading head. The invention has the advantage that, due to the markings on the conveyor - whereby these markings can be arranged on a measuring tape - it is possible to record the position and changes in the position of the workpiece at a measuring point with the aid of at least one reading head which is arranged in the area along the conveyor, for example below the conveyor element of the conveyor on which the workpiece is arranged. This allows the workpiece to be positioned precisely on the conveyor. The advantage of the method according to the invention, as well as the device according to the invention, is that no external structures are required.Movements of the conveyor – and thus the position of the workpiece on the conveyor – are recorded precisely and without play without the need for external structures using the markings assigned to the conveyor and at least one read head. The method and device according to the invention also have the advantage that, during back and forth movements, any "backlash" of the conveyor is taken into account and this "backlash" does not lead to incorrect positioning. Within the scope of the invention, it is possible to assign several read heads to the conveyor so that particularly large workpieces can be positioned precisely according to the invention (method and device). In this case, it can be provided that a higher-level computing unit weights the measurement results of the several read heads and controls the drive for the conveyor.In a preferred embodiment of the device according to the invention, the at least one read head is arranged below the upper belt of a conveyor link of the conveyor. The read head can thus detect position changes (= movements of the conveyor link) and the different tensions (= length changes in the conveyor link) via the markings assigned to the conveyor. For the drive of the conveyor, it can be provided that a computing unit evaluates the measurement results recorded in the read head, namely the number of markings assigned to the conveyor and detected by the read head, and controls the drive for the conveyor so that the workpiece to be processed is precisely positioned. In one possible embodiment, the invention uses a magnetic tape measuring system, whereby the function described below is possible: Magnetic tape sensors are magnetic length measuring systems that consist of two components: a read head and a magnetic tape.Relative movements of the magnetic tape relative to the read head are converted into analog or digital signals. Digital magnetic tape sensors can be absolute or incremental. Absolute sensors transmit their absolute position along the measuring path. This information is based on a special code pattern on the magnetic tape, which enables exact position determination without knowledge of the previous position. This allows the sensor position to be output precisely even after a power failure. Zeroing is not necessary with this sensor variant. The magnetic tape consists of a magnetic strip in which north and south poles alternate at regular intervals. A cover strip can also be attached to protect the magnetic strip. Magnetoresistive sensors or Hall sensors are located in the read head.These sensors detect the change between north and south poles as the magnetic tape moves over the read head and convert this change into an electrical signal. The signal is then processed into a corresponding output signal by subsequent electronics in the read head. Due to its design and the magnetic measuring principle, magnetic tape length measurement offers a number of advantages: - Because the read head moves contactlessly over the magnetic tape measuring system, the magnetic tape length measurement operates friction- and wear-free. - The absence of moving mechanical components, such as bearings, minimizes the risk of errors or failures. - The use of miniaturized sensor modules and circuits enables very compact and slim housings. - The fully enclosed sensor housings and the magnetic tapes, protected by the additional cover strip, achieve high protection classes from IP67 to IP69K.- The sensor systems are insensitive to light, dust, moisture, oil, grease, and a wide range of chemicals. In one possible embodiment of the invention, two read heads arranged at a defined distance from one another in a common carrier are used, so that changes in the distance between markings assigned to the conveying means can be precisely detected. In one possible implementation of the method according to the invention, this can be characterized, for example, in that magnetic markings and a read head that detects magnetic markings, or optical markings and an optical reading head, or capacitive markings and a capacitive reading head, or inductive markings and an inductive reading head are used as the markings.In one possible embodiment of the method according to the invention, this can be characterized, for example, in that a conveyor with an endlessly rotating conveyor link or a finite conveyor link is used as the conveyor link. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that a toothed belt or a flat belt is used as the conveyor link. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that a toothed belt, a V-belt, a flat belt, a chain, a rope or a wire is used as the conveyor link. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that the frictional connection between the workpiece and the conveyor is increased, in particular by applying negative pressure.In one possible embodiment of the method according to the invention, this can be characterized, for example, in that markings provided on a measuring tape connected to the conveyor are used. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that a longitudinally elastic measuring tape is used as the measuring tape. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that changes in the distance between markings on the conveyor, in particular on the measuring tape, are taken into account when the length of the conveyor and the measuring tape changes. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that relative movements between markings and reading head are converted into analog or digital signals.In one possible embodiment of the method according to the invention, this can be characterized, for example, in that the actual position of the workpiece on the conveyor is detected by detecting a pattern of markings on the measuring tape. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that the (initial) position of the workpiece on the conveyor is detected with a (position) sensor. In one possible embodiment of the method according to the invention, this can be characterized, for example, in that the (initial) position of a workpiece transported on the conveyor is detected.In one possible embodiment of the method according to the invention, this can be characterized, for example, by the fact that after the (initial) position of the workpiece has been detected, the actual position of the workpiece is detected using the number of markings detected by the reading head that have moved past the reading head. In one possible embodiment of the method according to the invention, this can be characterized, for example, by the use of separate drives for successively arranged conveyors, wherein machining of the workpiece is performed on a conveyor or between conveyors.In one possible embodiment of the method according to the invention, this can be characterized, for example, in that the drive of the at least one conveyor is controlled via a programmable logic controller (PLC controller) on the basis of the determined actual data and the target data for the position of the workpiece. In one possible embodiment of the device according to the invention, this can be characterized, for example, in that a magnetic measuring system, an optical measuring system, a capacitive measuring system or an inductive measuring system is provided as the measuring system. In one possible embodiment of the device according to the invention, this can be characterized, for example, in that the markings are provided on a measuring tape arranged on the conveyor. In one possible embodiment of the device according to the invention, this can be characterized, for example, in that the measuring tape is a longitudinally elastic measuring tape.In one possible embodiment of the device according to the invention, it can be characterized, for example, in that two reading areas active for detecting markings, which are at a defined distance from one another, are provided in the reading head. In one possible embodiment of the device according to the invention, it can be characterized, for example, in that the measuring tape is integrated into a conveyor element of the conveyor. In one possible embodiment of the device according to the invention, it can be characterized, for example, in that the conveyor element comprises a toothed belt, flat belt, V-belt, chain, rope or wire. In one possible embodiment of the device according to the invention, it can be characterized, for example, in that the measuring tape is a magnetic strip in which alternating north and south poles are provided as markings.In one possible embodiment of the device according to the invention, this can be characterized, for example, in that the measuring tape is protected by a cover strip. In one possible embodiment of the device according to the invention, this can be characterized, for example, in that magnetoresistive sensors or Hall sensors are provided in the reading head. In one possible embodiment of the device according to the invention, this can be characterized, for example, in that a sensor for determining the (initial) position of the workpiece is assigned to the conveyor. For example, the method according to the invention and the device according to the invention can be operated as follows: A workpiece is transported on a first conveyor to a starting position. A sensor detects the front edge of the workpiece and thus its starting position. At the same time, the reading head detects the position of the conveyor member.The workpiece is then positioned by detecting markings on the conveyor using at least one read head. To process the workpiece, it is moved, for example, back and forth, preferably horizontally along the desired path by the conveyor (or two consecutive conveyors). It is possible to move a processing tool up and down, i.e., transversely to the longitudinal extent of the conveyor, to process edges of the workpiece oriented transversely to the conveying direction. The drive of the conveyor or conveyors is controlled by a programmable logic controller (PLC) based on the determined position data or target data for the workpiece position.There are various possibilities for the markings, with particular consideration given to using magnetic markings and a read head that detects magnetic markings, or optical markings and an optical read head, or capacitive markings and a capacitive reading head, or inductive markings and an inductive reading head. Within the scope of the invention, it is also contemplated to string together several conveyors for positioning larger workpieces. To achieve precise positioning of the workpiece here as well, several read heads or one read head with two spaced-apart reading areas are used.When the center of gravity of the workpiece is shifted because it is moved, the distances between markings detected by the read heads(s) are weighted, with preference being given to the values ​​for the distances between markings detected in the area of ​​the center of gravity of the workpiece. In the method according to the invention and with the aid of the device according to the invention, the number of markings provided on the conveyor means that have moved past the stationary read head is detected by at least one read head and evaluated to determine the actual position of the conveyor means and thus the actual position of the workpiece in the device. Any stretching of the conveyor element of the conveyor means can preferably be taken into account by the read head detecting distances between successive markings and taking the detected distances into account when determining the actual position of the workpiece.The method and device according to the invention can be used for the precise positioning of workpieces during machining, as well as for measuring tasks and in processes where precise positioning of workpieces is important. Further details and features of the invention will become apparent from the following description of preferred exemplary embodiments with reference to the drawings. These show: Fig. 1 shows essential features of a device according to the invention, Fig. 2 shows a detail from Fig. 1, Fig. 3 shows part of a toothed belt as a conveyor link, Fig. 4 shows an enlarged detail of Fig. 3, Fig. 5 shows a conveyor link designed as a flat belt, Fig. 6 shows an example of a read head, Fig. 7 shows the assignment of a read head to a toothed belt as a conveyor link, Fig. 8 shows a representation similar to Fig. 7 with further details, Fig. 9 shows a conveyor device with two conveyor links, Fig.10a, b and c show a conveyor device with several conveyor elements arranged one after the other, and Fig. 11 shows a flow diagram for the signal processing during positioning according to the invention. A device 1 shown in Fig. 1 for transporting workpieces 2, such as glass panes or insulating glass blanks, comprises an elongated (or oblong) conveyor 3 which has a conveyor element 4. The conveyor element 4 is placed over a deflection wheel 5 and a drive wheel 6, to which a drive 7 is assigned. A workpiece 2 stands on the conveyor 4. When transporting glass panes and insulating glass blanks, toothed belts (cf. Fig. 3 and Fig. 4) are primarily used as conveyor elements 4 of conveyors 3. A reading head 10 is assigned to the upper belt 8 of the conveyor element 4. In the exemplary embodiment, the reading head 10 is arranged below the upper belt 8. As can be seen from the detail according to Fig.As can be seen from Fig. 2, markings 11 are provided on the conveyor link 4 and thus on the conveyor means 3. In the exemplary embodiment, the markings 11 are attached to the conveyor link 4 in the form of an elastic measuring tape 9. The reading head 10 has a sensor that detects the markings 11 and transmits the number of detected markings to the control of the device 1 according to the invention. Fig. 3 shows, as an example of a conveyor link 4, a toothed belt 12 in which tension carriers 13 are contained. Fig. 4 shows the arrangement of the markings 11 on the toothed belt 12. For example, the markings 11 are magnetic markings in the form of alternating north and south poles. As shown in Fig.5, a flat belt 14 can also be used as the conveyor link 4 instead of the toothed belt 12, wherein it is particularly advantageous that with the invention, slippage on the drive wheel 6 can be compensated for by measurement according to the invention with the aid of the markings 11 and the reading head 10 directly on the flat belt 14. Fig. 6 shows an example of a reading head 10 which has two reading areas 15 with sensors 16, so that due to the defined distance between the reading areas 15, changes in the distance between markings 11 on the conveyor link 4 can be detected. The reading head 10 is fixedly mounted on the frame of the (conveyor) device 1 and in particular aligned parallel to the upper belt 8 of the conveyor link 4, as shown in Fig. 7. Fig.Figure 8 illustrates how the reading head 10 with two reading areas 15 can detect the change in the pitch, i.e. the distance between the markings 11, and pass the information thus detected about changed distances "A" and "B" between markings 11 on to the control system of the device 1. As illustrated in Figure 9, a workpiece 2 is transported in by a first conveyor 3 and stopped, with a (position) sensor 20 detecting the initial position (starting position) of the workpiece 2. The movements of the workpiece 2 in order to transport it to the processing point 21 and to precisely align (position) it are detected by the reading heads 10 assigned to the two conveyors 3 by detecting markings 11. Figures 10a to 10c show that for larger workpieces 2, several conveyors 3 can also be arranged in series.In order to be able to precisely position the workpiece 2 for processing in this case as well, several reading heads 10 are used. Depending on the shift of the center of gravity "S" of the workpiece 2, the measurements recorded by the various reading heads 10 (number of recorded markings 11 and distance between the markings 11 from one another) are weighted differently, with measurement results in the area of ​​the center of gravity "S" of the workpiece 2 being emphasized during the weighting. The flow chart in Fig. 11 shows that several measurement results are entered into the PLC control of the drive 7 for the conveyor 3, whereby the actual value of the position of a workpiece 2 together with the distance between markings 11 on the conveyor 3 recorded by the reading head 10, in particular at two different locations (actual position value sensor 1 and actual position value sensor 2), are used. This confirms that more actual position values ​​and actual pitch values ​​can also be used.As mentioned above, the design of the conveyor 3 is not essential for the invention. For example, conveyors 3 that can be used for the invention can have conveyor belts, flat belts, toothed belts, V-belts, chains, ropes, wires, etc. as conveyor links 4, with toothed belts primarily being used for transporting glass panes. In summary, an exemplary embodiment can be described as follows: To position workpieces 2 on a conveyor 3, the position of the workpiece 2, which is moved by the conveyor 3, is detected with the aid of markings 11 assigned to the conveyor 3. For this purpose, the number of markings 11 assigned to the conveyor 3 that have moved past at least one stationary reading head 10 is recorded. In particular, markings 11 provided on a measuring tape 9 connected to the conveyor 3 are used.

Claims

Patent claims:

1. A method for positioning workpieces (2) on a conveyor (3), characterized in that the position of the workpiece (2), which is moved with the conveyor (3), is detected with the aid of markings (11) assigned to the conveyor (3), in that the number of markings (11) arranged on the conveyor (3) that move relative to a reading head (10) is detected by the at least one stationary reading head (10).

2. A method according to claim 1, characterized in that the markings (11) used are magnetic markings and a reading head that detects magnetic markings, or optical markings and an optical reading head that detects optical markings, or capacitive markings and a reading head that detects capacitive markings, or inductive markings and an inductive reading head that detects inductive markings. 3.Method according to claim 1 or 2, characterized in that a conveyor (3) with an endlessly rotating conveyor link (4) or a finite conveyor link (4) is used as the conveyor link (3).

4. Method according to claim 3, characterized in that a toothed belt (12) or a flat belt (14) is used as the conveyor link (4).

5. Method according to claim 3, characterized in that a toothed belt, a V-belt, a flat belt, a chain, a rope or a wire is used as the conveyor link (4).

6. Method according to one of claims 1 to 5, characterized in that the frictional connection between the workpiece (2) and the conveyor link (3) is increased in particular by applying negative pressure.

7. Method according to one of claims 1 to 6, characterized in that markings (11) provided on a measuring tape (9) connected to the conveyor (3) are used.

8. Method according to claim 7, characterized in that a longitudinally elastic measuring tape (9) is used as the measuring tape (9).

9. Method according to one of claims 1 to 8, characterized in that changes in the distance between markings (11) on the conveyor (3), in particular on the measuring tape (9), are taken into account when the length of the conveyor (3) and the measuring tape (9) changes.

10. Method according to one of claims 1 to 9, characterized in that relative movements between markings (11) and the reading head (10) are converted into analog or digital signals.Method according to one of claims 7 to 10, characterized in that the actual position of the workpiece (2) on the conveyor (3) is detected by detecting a pattern of markings (11) on the measuring tape (9).

12. Method according to one of claims 1 to 11, characterized in that the (initial) position of the workpiece (2) on the conveyor (3) is detected with a (position) sensor (20).

13. Method according to claim 12, characterized in that the (initial) position of a workpiece (2) transported on the conveyor (3) is detected.

14. Method according to claim 13, characterized in that after detecting the (initial) position of the workpiece (2), the detection of the actual position of the workpiece with. The method is carried out with the aid of the number of markings (11) detected by the reading head (10) that have moved past the reading head (10).

15. The method according to one of claims 1 to 14, characterized in that separate drives (7) are used for successively arranged conveyor means (3), wherein machining of the workpiece (2) is carried out on a conveyor means (3) or between conveyor means (3).

16. The method according to claim 15, characterized in that the drive (7) of the at least one conveyor means (3) is controlled via a programmable logic controller (PLC controller) on the basis of the determined actual data and the target data for the position of the workpiece (2).Device for carrying out the method according to one of claims 1 to 16, with at least one conveyor (3) and a drive (7) assigned to the conveyor (3), characterized in that the conveyor (3) has a measuring system which has markings (11) arranged on the conveyor (3) at defined distances from one another and at least one reading head (10) which detects markings (11) arranged on the conveyor (3).

18. Device according to claim 17, characterized in that a magnetic measuring system, an optical measuring system, a capacitive measuring system or an inductive measuring system is provided as the measuring system.

19. Device according to claim 17 or 18, characterized in that the markings (11) are provided on a measuring tape (9) arranged on the conveyor (3).

20. Device according to claim 19, characterized in that the measuring tape (9) is a longitudinally elastic measuring tape (9).

21. Device according to claim 20, characterized in that two reading areas (15) active for detecting markings (11) are provided in the reading head (10), which are at a defined distance from one another.

22. Device according to one of claims 19 to 21, characterized in that the measuring tape (9) is integrated into a conveyor member (4) of the conveyor means (3).

23. Device according to one of claims 17 to 22, characterized in that the conveyor means (3) has a toothed belt, flat belt, V-belt, chain, rope, or wire as the conveyor member (4).

24. Device according to one of claims 19 to 23, characterized in that the measuring tape (9) is a magnetic strip in which alternating north and south poles are provided as markings (11).

25. Device according to one of claims 19 to 24, characterized in that the measuring tape (9) is protected by a cover strip.Device according to claim 24 or 25, characterized in that magnetoresistive sensors or Hall sensors are provided in the reading head (10).

27. Device according to one of claims 17 to 26, characterized in that a sensor (20) for determining the (initial) position of the workpiece (2) is assigned to the conveying means (3).

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