EP2995421A1 - Wide strip grinding machine with a device for controlling the tension roller for generating a pre-defined grinding pattern and method therefor - Google Patents

Abstract

A wide-belt sander and a method in which the edge of a sanding belt (12) is detected by a position detector (22), the position detector (22) generates a continuous actual signal depending on the position of the sanding belt (12) , A controller (S) generates an oscillating signal, which is fed as a reference variable (w) to a controller (24) which controls an actuator (32) s, o, that the grinding belt (12) its position corresponding to the time course of the reference variable ( w) changes to produce a predetermined grinding pattern on a surface of a workpiece (18).

Description

The invention relates to a wide-belt sanding machine with a sanding belt, which is guided over a grinding roller and a position-controlled tensioning roller. Furthermore, the invention relates to an associated method.

For 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 abrasive belt is designed as an endless belt. With the length and width ratios used, it is difficult to center the belt over spherical rollers without additional control. To make matters worse still band tolerance and elongation are added.

Each of these effects, during operation of the abrasive belt, causes the abrasive belt to travel on the rollers in the direction of the axes of rotation of the rollers. Therefore, there is a need to monitor the position of the abrasive belt on the abrasive roller and actively counteract the movement of the abrasive belt in the axial direction of the abrasive roller.

In the DE 33 31429 A1 a control is described in which the position of the edge of the sanding belt is detected with a light barrier. A pneumatic adjusting member is used to control the abrasive belt. Due to the control of the adjusting member is continuously operated, which is a continuous oscillation of the grinding belt with a certain hysteresis Episode has. The resulting traces of oscillation significantly affect the grinding result.

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

DE 10 2007 012 580 A1 describes a method for guiding the tape of a belt grinding machine, in which the lateral position of an abrasive belt is detected by means of an analog edge sensor. The signals from the analog edge sensor are fed to an electropneumatic governor, which regulates the pressure of a pneumatic oscillation cylinder, resulting in a nearly stationary abrasive belt. In order to carry out a conventional oscillation movement, the signal of the analog edge sensor can be acted upon via a control unit, so that a tensioning roller pivots about a pivot point.

DE 11 38 658 A describes a device for regulating and controlling the running of abrasive belts on belt grinders. A motor drive controls a pivotable tape roll to perform continuous, uniform forced oscillations about a swing axis. The frequency and amplitude of the vibrations is adjustable.

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

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

In the wide belt sander of the invention, the abrasive belt is passed over a sanding roller and a tension roller. The tensioning roller is adjustable in its position by means of an actuator in such a way that the grinding belt occupies a predetermined position on the grinding roller. For detecting the actual position of the grinding belt on the grinding roller, the position of an edge of the grinding belt is detected by means of a position detector, e.g. a photocell detected. This light barrier comprises a beam source and a detector. With the light barrier, the edge of the sanding belt is captured in a silhouette process. Thus, the detector generates a continuous analog actual signal, which is dependent on the position of the grinding belt with respect to the light barrier and thus also with respect to the position of the grinding belt on the grinding roller. The analog actual signal is fed to a controller which controls the actuator continuously so that by changing the position of the tensioning roller, the grinding belt on the grinding roller maintains a predetermined position.

According to the invention, a controller generates an oscillating signal, which is supplied as a reference variable to the controller. This controller controls the actuator so that the abrasive belt changes its lateral position with respect to the light barrier according to the time course of the reference variable. Accordingly, in conjunction with the forward movement of the workpiece under the abrasive roller, a grinding pattern defined by the guide size results.

The controller may generate as oscillating signal, for example, a sinusoidal signal, a triangular signal, a trapezoidal signal or an overlay of these signals. Accordingly, as a grinding pattern along the workpiece surface, a sinusoidal pattern, a triangular pattern, a trapezoidal pattern or an overlay of these patterns result. It should be noted that in the steady state of the control loop, the disturbances, e.g. a random emigration of the movement of the grinding belt, are corrected and no longer occur such disturbances in the grinding pattern.

In order to produce attractive grinding patterns, the oscillating signal generated by the controller may include time periods with constant signal level in its time course. These are expressed in the grinding pattern as path sections with a constant abrasive structure.

It is advantageous if the controller comprises a function generator for generating periodic and non-periodic signals. In this way, a variety of waveforms can be provided for the command variable, resulting in a wide range of patterns.

It is particularly advantageous if the controller is designed as a programmable logic controller (PLC). Such a controller has a modular construction and is easy to adjust in its application by an operator, so that a high flexibility in the selection of a desired grinding pattern is given.

As a position detector, in addition to the above-mentioned forked light barrier, an optical reflex sensor, a mechanical contactor, a capacitive or inductive sensor, an ultrasonic sensor or a compressed air sensor, e.g. according to the nozzle-flapper principle works to be used. It is essential that the position detector used in each case detects the web edge continuously and continuously images its position in a signal, preferably analog.

In an advantageous embodiment, the actuator is pneumatic and comprises at least one bellows cylinder, which operates against a restoring element. These bellows cylinders have no slip-stick effect, whereby the control process is more continuous. Alternatively, a pneumatic muscle cylinder with similar functional behavior can be used.

In an advantageous embodiment of the belt grinding machine, the axis of rotation of the tensioning roller is adjustable 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 particularly simple.

In an advantageous development of the controller is a proportional controller. This proportional controller is particularly simple in construction and can be easily implemented, e.g. in the form of a solenoid valve which adjusts the pneumatic pressure supplied to the actuator.

In another development, the control loop additionally has an integral and / or differential behavior. This integral behavior of the control loop improves the control to minimize the permanent setpoint value deviation typical of a proportional controller. A differential behavior increases the control speed of the control loop.

It is particularly advantageous if the tensioning roller is centrally supported by means of a tower shaft and can be rotated about the longitudinal axis of the tower shaft. A gimbal is achieved when the tension roller is mounted so that it can oscillate about a third axis which is aligned perpendicular to the longitudinal axis of the tower shaft. By this suspension, the tension roller can be particularly easily aligned so that a grinding belt with different circumferential lengths touches the tension roller at each point.

In another development of the wide-belt sanding machine, the sanding roller is driven by motor means. This improves the control in that the mass of the drive does not have to be moved with the tension roller from the actuator. As a result, the actuator can be constructed simpler.

According to another aspect of the invention, there is provided a method of producing predetermined abrasive 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 will be explained below with reference to an embodiment with reference to the figures. Show in it

FIG. 1

a schematic structure of a control loop for position control of an abrasive belt,

FIG. 2

a schematic structure of a detector,

FIG. 3

a layer of tension roller and sanding belt after FIG. 1 at an adjustment by the regulator, and

FIG. 4

possible positions of the tension roller after FIG. 3 according to the section AA.

FIG. 1 shows a schematic structure of a control loop 10 for position control of an abrasive belt 12. The sanding belt 12 is guided over a tension roller 14 and a grinding roller 16. The sanding roller 16 presses the sanding belt 12 onto a workpiece 18 to be sanded.

The sanding belt 12 is an endless sanding belt with a width of up to about 3 meters. Due to the manufacturing process, such an abrasive belt 12 is not quite uniform, ie the circumference at one edge of the belt usually differs from the circumference at the other edge of the belt. Therefore, in the grinding operation, the grinding belt 12 tends to emigrate along a rotation axis 20 of the grinding roller 16 in the predetermined direction in addition to the rotation direction indicated by the arrow P1. The lateral movement in the direction of the axis of rotation 20 is a disturbance. With the help of the control loop 10, the position of the grinding belt 12 is monitored on the grinding roller 16 and counteracts the disturbing movement actively.

An in FIG. 2 Depending on the position of the band edge, a detector in the light barrier 22 generates a continuous analog actual signal. Preferably, the analog actual signal is a DC signal, in this embodiment, a voltage between 0 volts and +10 volts. In this case, a signal of 0 volts corresponds to a position of the belt edge of the sanding 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 sanding belt 12 at the other detection limit of the light barrier 22.

This analog actual signal is according to FIG. 1 a controller 24 which provides the pneumatic pressure for a pneumatic actuator. Furthermore, the controller 24 may be supplied in a variant of a generated by a desired value encoder 26 analog target signal. The desired signal corresponds to a desired position of the sanding belt 12 on the sanding roller 16. At the desired value encoder 26, the desired position of the sanding belt 12 is adjustable.

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

In a general embodiment, the controller 24 comprises a summing element 28 and a proportional controller 30. The summing element 28 is supplied with desired signal and actual signal. The formed deviation between Target signal and actual signal is supplied to the proportional controller 30, which generates a corresponding control signal. This exemplary pneumatic signal may process the pneumatic actuator 32.

The actuator 32, which includes, for example, a bellows cylinder, changes the position of a rotation axis 34 of the tension roller 14 to the effect that the grinding belt 12 complies with the target position predetermined by the desired signal on the grinding roller 16. The change in position of the rotation axis 34 will later in the Figures 3 and 4 described.

FIG. 2 shows as an example of a position detector, the light barrier 22, which is a fork light barrier in this embodiment, in which the abrasive belt 12 is immersed 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, light-emitting diode 36 and detector 38 are optimally aligned with one another on a U-shaped carrier 39. The edge of the sanding belt 12 is guided in such a way that, in its desired position on the sanding roller 16, it partially covers a light beam 40 emitted by the light-emitting diode 36 and thus partially shades 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 depends on the position of the band edge of the grinding belt 12. If the sanding belt 12 covers the entire light beam 40, then the detector 38 will output a signal of 0 volt. If the light beam 40 at the detector 38 is not shadowed by the abrasive belt 12 at all, then the detector 38 will output a signal of 10 volts. In a partial shading of the detector 38th the voltage signal of the detector 38 is proportional to the shading and thus dependent on the position of the grinding belt 12.

FIG. 3 shows a position of the tension roller 14 and the grinding belt 12 in an adjustment of the position of the tension roller 14 by the actuator 32. This actuator 32 has the position of the axis of rotation 34 of the tension roller 14 changed so that it occupies the position shown in dashed lines 14 '.

How out FIG. 4 shows, the tension 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 so as to provide the positions shown at 44 'and 44 "by the reference numerals 42, 42' and 42" Tensioning roller 14 denotes.

The tower shaft 46 supports the tension roller 14 in the center and can pivot about the rotation axis 15. If the tension roller 14 is gimbal connected to the tower roller 46 (gimbal suspension), it can also be pivoted in a third axis perpendicular to the axis of rotation 15, wherein the paper plane of the FIG. 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 sanding belts 12 of different lengths and to enable the replacement of sanding belts. In this case, the tensioning roller 14 is aligned by a movement about the third axis in such a way that the grinding belt 12 touches the tensioning roller 14 at each point of the tensioning roller 14. For generating a desired grinding pattern on the surface of the workpiece 18, the control circuit 10 (FIG. FIG. 1 ) controlled by the controller S, which is advantageously designed as a programmable logic controller (PLC). The signal generated by this control S is supplied as a reference variable w the controller 24, which controls the actuator 32 so that the grinding belt 12 changes its lateral position according to the time course 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 follows in the steady state of the control loop 10 in close approximation to the time course of the reference variable w. By the action of the control loop 10 and random disturbances are regulated, which can occur, for example, due to the unevenness of the grinding belt 12.

It is advantageous if the controller S comprises a preferably programmable function generator, with the aid of which periodic and non-periodic signals can be generated. For example, the signal generated by the controller in its time course may contain time segments with constant signal level. Here, the control circuit 10 causes a constant grinding pattern to be generated along a path on the surface of the workpiece. It is also possible to superimpose different sinusoidal signals, which lead to different time profiles of the reference variable w in accordance with the composition of Fourier components, thereby providing the user with a broad spectrum of grinding patterns for surfaces of workpieces.

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

Another development provides that a plurality of 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 supplies the associated signal profile to the controller 24 as a reference variable w and the wideband grinding machine thus controlled generates the grinding pattern on the surface of the workpiece.

LIST OF REFERENCE NUMBERS

10

loop

12, 12 '

sanding belt

14, 14 ', 14 "

tension roller

15

axis of rotation

16

grinding roll

18

workpiece

20

axis of rotation

22

photocell

24

regulator

26

Setpoint generator

28

summing

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 tension roller

44; 44 ', 44 "

End of the tension roller

46

tower shaft

P1

arrow

S

control

w

command variable

Claims (14)

Wide-belt sanding machine with a sanding belt (12) which is guided over a sanding roller (16) and a tensioning roller (14),
wherein the tensioning roller (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 roller (16),
the position of an edge of the sanding belt (12) is detected by a position detector (22),
the position detector (22) generates a continuous actual signal as a function of the position of the grinding belt (12),
and wherein the actual signal is fed to a controller (24) which continuously controls the actuator (32) so that the grinding belt (12) on the grinding roller (16) maintains a predetermined position, characterized
in that a controller (S) generates an oscillating signal which is fed to the controller (24) as a reference variable (w), and in that the controller (24) controls the actuator (32) so that the grinding belt (12) moves in accordance with the changes over time of the reference variable (w) in order to produce a predetermined grinding pattern on a surface of a workpiece (18). Wide-belt sanding machine according to claim 1, characterized in that the position detector as a light barrier (22), as an optical reflex sensor, as a mechanical Contactor, is designed as a capacitive or inductive sensor, as an ultrasonic sensor or as a compressed air sensor. Wide-belt sanding machine according to claim 1 or 2, characterized in that the actuator is a pneumatic actuator (32) or a motor actuator is provided. Wide-belt sanding machine according to claim 3, characterized in that the actuator (32) comprises at least one bellows cylinder. Wide-belt sanding 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. Wide-belt sanding machine according to one of the preceding claims, characterized in that the controller (24) comprises a proportional controller (30). Wide-belt sanding machine according to claim 5, characterized in that the control circuit (10) has an integral and / or differentiating behavior. Wide-belt sanding machine according to one of the preceding claims, characterized in that the tensioning roller (14) is gimballed. Wide belt sander according to one of the preceding claims, characterized in that the controller (S) as an oscillating signal Sinusoidal signal, a triangular signal, a trapezoidal signal or an overlay generated from these signals. Wide-belt sanding machine according to claim 9, characterized in that the oscillating signal contains in its time course periods of constant signal level. Wide belt sander according to one of the preceding claims, characterized in that the controller (S) comprises a preferably programmable function generator for generating periodic and non-periodic signals which form the oscillating signal. A method of grinding the surface of a workpiece with a wide belt sander comprising a sanding belt (12) passed over a sanding roller (16) and a tension roller (14),
in which the tensioning roller (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 roller (16),
the position of an edge of the sanding belt (12) is detected by a position detector (22),
the position detector (22) generates a continuous actual signal as a function of the position of the grinding belt (12),
and in which the actual signal is supplied to a controller (24) which continuously controls the actuator (32) so that the grinding belt (12) on the grinding roller (16) maintains a predetermined position, characterized
in that an oscillating signal is generated by a controller (S) which is fed as a reference variable (w) to the controller (24),
and that the controller (24) controls the actuator (32) so that the abrasive belt (12) changes its position in accordance with the timing of the guide amount (w) to a predetermined grinding pattern (S) on the surface of the workpiece (18) produce. A method according to claim 11, characterized in that a target grinding pattern is provided, with the aid of the controller (S) a signal curve for the oscillating signal is generated, which corresponds to the desired grinding pattern or comes as close as possible,
and that this waveform is supplied to the controller (24) as a reference variable (w). A method according to claim 12 or 13, characterized in that a plurality of grinding patterns and the associated signal waveforms for the oscillating signal are stored in a memory, and that the controller (S) in selecting one of the grinding patterns, the associated waveform to the controller (24) as a reference variable ( w) feeds.

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