EP2995421B1 - Wide strip grinding machine with a device for controlling the tension roller for generating a pre-defined grinding pattern and method therefor - Google Patents

Description

The invention relates to a wide-belt sanding machine with a sanding belt that is guided over a sanding roller and a position-controlled tensioning roller. The invention also relates to an associated method.

In the case of wide belt sanders, the sanding belt is stretched over at least two rollers. Here, one of the rollers serves as a grinding roller and the other roller as a tensioning roller. The sanding belt is designed as an endless belt. With the length and width ratios used, it is difficult to center the belt using crowned rollers without additional control. Tape tolerance and elongation make things even more difficult.

During operation of the grinding belt, each of these effects means that the grinding belt can migrate on the rollers in the direction of the axes of rotation of the rollers. There is therefore a need to monitor the position of the grinding belt on the grinding roller and to actively counteract the movement of the grinding belt in the axial direction of the grinding roller.

In the DE 33 31 429 A1 a control is described in which the position of the edge of the grinding belt is detected with a light barrier. A pneumatic actuator is used to control the sanding belt. Due to the control, the adjustment member is continuously actuated, resulting in a continuous oscillation of the grinding belt with a certain hysteresis result. The resulting oscillation marks have a significant impact on the grinding result.

the DE 20 2012 100 928 U1 from Hans Weber Maschinenfabrik describes a wide belt sanding machine with a position-controlled tension roller. By specifying a constant target value, the random oscillation of the sanding belt is effectively prevented.

DE 10 2007 012 580 A1 , which forms the basis for the preambles of claims 1 and 11, describes a method for belt guidance of a belt grinding machine, in which the lateral position of a grinding belt is detected by means of an analogue edge sensor. The signals from the analogue edge sensor are fed to an electro-pneumatic controller which regulates the pressure of a pneumatic oscillating cylinder, resulting in an almost stationary sanding belt. To carry out a conventional oscillating movement, a control unit can be used to act on the signal from the analog edge sensor, so that a stretching roller pivots about a pivot point.

DE 11 38 658 A describes a device for adjusting and controlling the running of grinding belts on belt grinding machines. A motor drive controls a pivotable tape roller in such a way that it executes continuous, uniform, forced vibrations about a vibration axis. The frequency and amplitude of the vibrations is adjustable.

US 6,126,102 A relates to a device and a method for chemical-mechanical polishing of wafers in semiconductor technology. During the polishing process, a rotating wafer is replaced by a linearly moving one Polishing tape polished. Such a polishing belt has a specific texture, which means that a periodic pattern can form on the surface of the wafer, which is undesirable. Therefore, the polishing belt is moved laterally by a sinusoidal or other periodic or non-periodic motion, resulting in smoothing of the polishing pattern on the surface of the wafer.

US 6,899,594 B1 also relates to chemical-mechanical polishing (CMP—chemical mechanical polishing) for wafers in the semiconductor industry. In a manner similar to the aforementioned document, a rotating wafer is polished by a linearly moving polishing belt. A specific lateral movement pattern, eg sinusoidal, rectangular, etc., is applied to the polishing belt in order to smooth out any traces of polishing.

It is an object of the invention to provide a wide belt sander and method that produces a predetermined oscillating sanding pattern on the workpiece.

This object is achieved with the features of claim 1 for a wide belt sander. Advantageous developments are specified in the dependent claims.

In the wide belt sander according to the invention, the sanding belt is guided over a sanding roller and a tensioning roller. The position of the tension roller can be adjusted by means of an actuator in such a way that the grinding belt assumes a predetermined position on the grinding roller. To record the actual position of the grinding belt on the grinding roller, the position of an edge of the grinding belt is detected using a position detector, e.g. a light barrier. This light barrier includes a beam source and a detector. The edge of the sanding belt is detected with the light barrier using a silhouette method. The detector thus generates a continuous analogue actual signal which is dependent on the position of the grinding belt in relation to the light barrier and therefore also in relation to the position of the grinding belt on the grinding roller. The analog actual signal is supplied to a controller which continuously controls the actuator in such a way that the grinding belt on the grinding roller maintains a predetermined position by changing the position of the tensioning roller.

According to the invention, a controller generates an oscillating signal that is fed to the controller as a reference variable. This controller controls the actuator in such a way that the grinding belt changes its lateral position in relation to the light barrier in accordance with the time profile of the reference variable. Accordingly, in conjunction with the advancement of the workpiece under the sanding roll, a command defined sanding pattern results.

The controller can generate, for example, a sinusoidal signal, a triangular signal, a trapezoidal signal or a superimposition of these signals as the oscillating signal. Accordingly, a sinusoidal pattern, a triangular pattern, a trapezoidal pattern or a superimposition of these patterns result as a grinding pattern along the workpiece surface. It should be noted that when the control circuit is in a steady state, the disturbance variables, e.g. a random deviation in the movement of the grinding belt, are also corrected and such disturbances no longer occur in the grinding pattern.

In order to generate an appealing sanding pattern, the oscillating signal generated by the controller can contain periods of time with a constant signal level in its course over time. These are reflected in the sanding pattern as path sections with a constant sanding structure.

According to the invention, the controller includes a function generator for generating periodic and non-periodic signals.

In this way, a large number of signal forms can be provided for the reference variable, which leads to a wide spectrum of grinding patterns.

Furthermore, it is particularly advantageous that the controller is designed as a programmable logic controller (PLC). Such a control has a modular structure and its application can be easily adjusted by an operator, so that there is a high degree of flexibility when selecting a desired grinding pattern.

In addition to the already mentioned fork light barrier, an optical reflex sensor, a mechanical contactor, a capacitive or inductive sensor, an ultrasonic sensor or a compressed air sensor, which works according to the nozzle-flapper principle, can be used as a position detector. It is essential that the position detector used in each case continuously detects the web edge and continuously maps its position in a signal, preferably analog.

In an advantageous embodiment, the actuator is pneumatic and includes at least one bellows cylinder that works against a restoring element. These air actuators do not have a slip-stick effect, which means that the control process is more continuous. Alternatively, a pneumatic muscle cylinder with a similar functional behavior can also be used.

In an advantageous embodiment of the belt grinding machine, the axis of rotation of the tensioning roller can be adjusted in at least one plane. It is particularly advantageous if this plane is selected parallel to the material surface to be ground. As a result, the actuator can be constructed in a particularly simple manner.

In an advantageous development, the controller is a proportional controller. This proportional controller has a particularly simple design and is easy to implement, e.g. in the form of a solenoid valve, which adjusts the pneumatic pressure supplied to the actuator.

In another development, the control loop also has an integral and/or differential behavior. This integral behavior of the control loop improves the control in such a way that the permanent setpoint value deviation typical of a proportional controller is minimized. A differential behavior increases the control speed of the control loop.

It is particularly advantageous if the tensioning roller is supported centrally by means of a tower shaft and can be rotated about the longitudinal axis of the tower shaft. Cardanic suspension is achieved when the tension roller is mounted in such a way that it can oscillate about a third axis, which is aligned perpendicularly to the longitudinal axis of the tower shaft. With this suspension, the tensioning roller can be aligned particularly easily in such a way that a grinding belt with different circumferential lengths touches the tensioning roller at every point. In another development of the wide belt sander, the sanding roller is driven by a motor. This improves the control in that the mass of the drive does not have to be moved by the actuator with the tension roller. As a result, the actuator can be constructed more simply.

According to a further aspect of the invention there is provided a method according to claim 11 for producing predetermined grinding patterns on the surface of a workpiece. The technical advantages that can be achieved with the method have already been described in connection with the device.

Figur 1

einen schematischen Aufbau eines Regelkreises zur Lageregelung eines Schleifbandes,

Figur 2

einen schematischen Aufbau eines Detektors,

Figur 3

eine Lage von Spannwalze und Schleifband nach Figur 1 bei einer Verstellung durch den Regler, und

Figur 4

mögliche Lagen der Spannwalze nach Figur 3 entsprechend dem Ausschnitt A-A.

The invention is explained below using an exemplary embodiment with reference to the figures. show in it

figure 1

a schematic structure of a control circuit for position control of a grinding belt,

figure 2

a schematic structure of a detector,

figure 3

one layer of tension roller and sanding belt figure 1 in the event of an adjustment by the controller, and

figure 4

possible positions of the tension roller figure 3 corresponding to section AA.

figure 1 shows a schematic structure of a control circuit 10 for controlling the position of a grinding belt 12. The grinding belt 12 is guided over a tensioning roller 14 and a grinding roller 16. The grinding roller 16 presses the grinding belt 12 onto a workpiece 18 to be ground.

The grinding belt 12 is an endless grinding belt with a width of up to about 3 meters. Due to the manufacturing process, such a grinding belt 12 is not entirely uniform, ie the circumference at one belt edge usually differs from the circumference at the other belt edge. Therefore, in the grinding operation, the grinding belt 12 tends to migrate along a rotational axis 20 of the grinding roller 16, in addition to the direction of rotation indicated by the arrow P1. The lateral movement in the direction of the axis of rotation 20 is a disturbance variable. The position of the grinding belt 12 on the grinding roller 16 is monitored with the aid of the control circuit 10 and the disturbing movement is actively counteracted.

one inside figure 2 The light barrier 22 shown monitors the position of the belt edge of the grinding belt 12. Depending on the position of the belt edge, a detector in the light barrier 22 generates a continuous analog actual signal. The analog actual signal is preferably a DC voltage signal, in this exemplary embodiment a voltage between 0 volts and +10 volts. A signal of 0 volts corresponds to a position of the belt edge of the grinding belt 12 at one end of the detection range of the light barrier 22, while a signal of +10 volts means a position of the belt edge of the grinding belt 12 at the other detection limit of the light barrier 22.

This analog actual signal is in accordance with figure 1 supplied to a regulator 24, which provides the pneumatic pressure for a pneumatic actuator. Furthermore, in one variant, the controller 24 can be supplied with an analog desired signal generated by a desired value generator 26 . The desired signal corresponds to a desired position of the grinding belt 12 on the grinding roller 16. The desired position of the grinding belt 12 can be set at the desired value transmitter 26.

It is particularly advantageous if, instead of setpoint value generator 26, the input of controller 24 is connected via a switching device 29 to the output of a controller S, which optionally supplies oscillating signals to controller 24 as reference variable w. A sinusoidal signal, a trapezoidal signal and a triangular signal for the controller S are shown as examples of signals.

In a general embodiment, the controller 24 includes a summing element 28 and a proportional controller 30. The summing element 28 is supplied with the desired signal and the actual signal. The formed control deviation between The desired signal and the actual signal are fed to the proportional controller 30, which generates a corresponding control signal. The pneumatic actuator 32 can process this exemplary pneumatic signal.

The actuator 32, which comprises a bellows cylinder, for example, changes the position of a rotational axis 34 of the tensioning roller 14 such that the grinding belt 12 maintains the desired position on the grinding roller 16 predetermined by the desired signal. The change in position of the axis of rotation 34 is later in the Figures 3 and 4 described.

figure 2 shows the light barrier 22 as an example of a position detector, which in this embodiment is a forked light barrier into which the grinding belt 12 dips with its side edge. The fork light barrier 22 comprises a large-area light-emitting diode as a beam source 36 and a phototransistor 38 optimized for an emission wavelength of the light-emitting diode 36. In the fork light barrier 22, the light-emitting diode 36 and detector 38 are optimally aligned with one another on a U-shaped carrier 39. The edge of the grinding belt 12 is guided in such a way that in its desired position on the grinding roller 16 it partially covers a light beam 40 emitted by the light-emitting diode 36 and thus partially shadows the detector 38 . The electrical signal generated by the detector 38 is proportional to the amount of light arriving at the detector 38, which in turn is dependent on the position of the belt edge of the abrasive belt 12. If the abrasive belt 12 obscures the entire light beam 40, the detector 38 will output a 0 volt signal. If the light beam 40 at the detector 38 is not shadowed at all by the grinding belt 12, the detector 38 will output a signal of 10 volts. In the case of partial shadowing of the detector 38 the voltage signal of the detector 38 is proportional to the shading and thus dependent on the position of the grinding belt 12.

figure 3 shows a position of the tension roller 14 and the grinding belt 12 when the position of the tension roller 14 is adjusted by the actuator 32. This actuator 32 has changed the position of the axis of rotation 34 of the tension roller 14 such that it assumes the position 14' shown in dashed lines.

How out figure 4 shows, the tensioning roller 14 is mounted centrally by a tower shaft 46 and can be pivoted about an axis of rotation 15 . The actuator 32 engages the end 44 of the tension roller 14 and pivots this end 44 about the axis of rotation 15, resulting in the positions shown with 44' and 44". Tension roller 14 called.

The tower shaft 46 supports the tensioning roller 14 in the middle and can pivot it about the axis of rotation 15 . If the tension roller 14 is cardanically connected to the tower roller 46 (cardanic suspension), it can also be pivoted in a third axis perpendicular to the axis of rotation 15, whereby it is the plane of the paper figure 4 leaves.

The tensioning roller 14 can be moved in the direction of the longitudinal axis of the tower shaft 46 in order to be able to tension grinding belts 12 of different lengths and to enable the replacement of grinding belts. The tensioning roller 14 aligns itself by moving about the third axis in such a way that the grinding belt 12 touches the tensioning roller 14 at every point on the tensioning roller 14 .

In order to produce a desired grinding pattern on the surface of the workpiece 18, the control circuit 10 ( figure 1 ) controlled via the controller S, which is advantageously designed as a programmable logic controller (PLC). The signal generated by this controller S is supplied as a reference variable w to the controller 24, which controls the actuator 32 in such a way that the grinding belt 12 changes its lateral position in accordance with the time profile of the reference variable w. As a result of the constant forward movement of the workpiece 18, a grinding pattern is generated on its surface, which in the steady state of the control circuit 10 closely follows the time profile of the command variable w. The action of the control circuit 10 also eliminates random disturbances that can occur, for example, as a result of the irregularity of the abrasive belt 12.

It is advantageous if the controller S includes a preferably programmable function generator, with the help of which periodic and non-periodic signals can be generated. For example, the time profile of the signal generated by the controller can contain time segments with a constant signal level. Here, the control circuit 10 causes a constant grinding pattern to be produced along a path on the surface of the workpiece. It is also possible to superimpose different sinusoidal signals, which, depending on the composition of Fourier components, lead to different time profiles of the command variable w, which provides the user with a wide range of grinding patterns for workpiece surfaces.

It is also possible for a user to sketch a desired grinding pattern for a desired surface structure. With the help of the controller S and the programmable function generator, a signal profile for the oscillating signal can then be generated, which belongs to the desired grinding pattern or comes as close as possible to it. This signal curve is supplied to the controller 24 as a reference variable w, whereupon the belt grinding machine generates this target grinding pattern during the grinding process, or generates a pattern which comes as close as possible to this.

Another development provides that several grinding patterns and the associated signal curves for the oscillating signal are stored in a memory. A user can then select one of these different grinding patterns. The controller S then feeds the associated signal curve to the controller 24 as a reference variable w, and the wide belt sander controlled in this way produces the sanding pattern on the surface of the workpiece.

Reference List

10

control loop

12, 12'

sanding belt

14, 14', 14"

idler roller

15

axis of rotation

16

sanding roller

18

workpiece

20

axis of rotation

22

Photoelectric barrier

24

controller

26

setpoint adjuster

28

summing element

29

switching element

30

proportional controller

32

actuator

34, 34', 34"

axis of rotation

36

led

38

phototransistor

39

carrier

40

beam of light

42, 42', 42"

end of the idler roller

44; 44', 44"

end of the idler roller

46

tower wave

P1

arrow

S

steering

w

benchmark

Claims (11)

1. Wide-belt grinding machine having a grinding belt (12) which is led over a grinding roll (16) and a tensioning roll (14),

   wherein the tensioning roll (14) is adjustable in its position by means of an actuator (32) in such a way that the grinding belt (12) assumes a predetermined position on the grinding roll (16),

   the position of an edge of the grinding belt (12) is detected by a position detector (22),

   the position detector (22) is configured to generate a continuous measured signal depending on the position of the grinding belt (12),

   wherein the wide-belt grinding machine is configured to feed the signal to a closed-loop controller (24), which controls the actuator (32) continuously in such a way that the grinding belt (12) maintains a predetermined position on the grinding roll (16),

   characterized in that an open-loop controller (S) is configured to generate an oscillating signal which is supplied as a reference variable (w) to the closed-loop controller (24) of a control loop (10), and in that the closed-loop controller (24) is configured to control the actuator (32) in such a way that the grinding belt (12) changes its position in accordance with the time profile of the reference variable (w) in order to produce a predefined grinding pattern on a surface of a workpiece (18) that is constantly moved forward,

   wherein the workpiece (18) is moved under the grinding roll (16) and the grinding roll (16) presses the grinding belt (12) onto the workpiece (18) to be ground, wherein, as a result of a constant forward movement of the workpiece (18), a grinding pattern is produced on its surface which, in the settled state of the control loop (10), follows the time profile of the reference variable (w) to a close approximation,

   wherein the open-loop controller (S) comprises a programmable function generator, which is configured to generate periodic and non-periodic signals which form the oscillating signal as a reference variable (w),

   and wherein a plurality of grinding patterns and the associated signal profiles for the oscillating signal are stored in a memory and, when one of the grinding patterns is selected, the open-loop controller (S) feeds the associated signal profile to the closed-loop controller (24) as the reference variable (w).
2. Wide-belt grinding machine accorded to Claim 1, characterized in that the position detector is designed as a light barrier (22), as an optical reflex sensor, as a mechanical contactor, as a capacitive or inductive sensor, as an ultrasonic sensor or as a compressed=air sensor.
3. Wide-belt grinding machine according to Claim 1 or 2, characterized in that the actuator provided is a pneumatic actuator (32) or a motorized actuator.
4. Wide-belt grinding machine according to Claim 3, characterized in that the actuator (32) comprises at least one bellows cylinder.
5. Wide-belt grinding machine according to one of the preceding claims, characterized in that the axis of rotation (34) of the tensioning roller (14) is adjustable in at least one plane.
6. Wide-belt grinding machine according to one of the preceding claims, characterized in that the closed-loop controller (24) comprises a proportional controller (30) .
7. Wide-belt grinding machine according to Claim 5, characterized in that the control loop (10) has an integral and/or differential response.
8. Wide-belt grinding machine according to one of the preceding claims, characterized in that the tensioning roll (14) is gimballed.
9. Wide-belt grinding machine according to one of the preceding claims, characterized in that the open-loop controller (S) generates a sinusoidal signal, a triangular signal, a trapezoidal signal or a superposition of these signals as the oscillating signal.
10. Wide-belt grinding machine according to Claim 9, characterized in that the oscillating signal contains time segments of constant signal height in its time profile.
11. Method for grinding the surface of a workpiece by using a wide-belt grinding machine, comprising a grinding belt (12) which is led over a grinding roll (16) and a tensioning roll (14),

    in which the tensioning roll (14) is adjustable in its position by means of an actuator (32) in such a way that the grinding belt (12) assumes a predetermined position on the grinding roll (16),

    the position of an edge of the grinding belt (12) is detected by a position detector (22),

    the position detector (22) generates a continuous measured signal depending on the position of the grinding belt (12),

    and in which the measured signal is fed to a closed-loop controller (24), which controls the actuator (32) continuously in such a way that the grinding belt (12) maintains a predetermined position on the grinding roll (16),

    characterized in that an open-loop controller (S) generates an oscillating signal which is supplied as a reference variable (w) to the closed-loop controller (24) of a control loop (10), and

    in that the closed-loop controller (24) controls the actuator (32) in such a way that the grinding belt (12) changes its position in accordance with the time profile of the reference variable (w) in order to produce a predefined grinding pattern (S) on a surface of a workpiece (18) that is constantly moved forward, wherein the workpiece (18) is moved under the grinding roll (16) and the grinding roll (16) presses the grinding belt (12) onto the workpiece (18) to be ground, wherein, as a result of a constant forward movement of the workpiece (18), a grinding pattern is produced on its surface which, in the settled state of the control loop (10) follows the time profile of the reference variable (W) to a close approximation,

    wherein the open-loop controller (S) comprises a programmable function generator for generating periodic and non-periodic signals which form the oscillating signal as a reference variable (w),

    and wherein a plurality of grinding patterns and the associated signal profiles for the oscillating signal are stored in a memory and, when one of the grinding patterns is selected, the open-loop controller (S) feeds the associated signal profile to the closed-loop controller (24) as the reference variable (w).

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