DE2152648A1 - Method and device for regulating the speed of rotation of a roller - Google Patents

Description

AGi ¹ A-GEYAEET AG LEVERKUSEN

Method and device for regulating the speed of rotation

a role.

Priority: Great Britain, October 23, 1970? Arm No. 50 498/70

This invention relates to a method and apparatus for regulating the speed of rotation of a roller, particularly a film or paper web-bearing roll to make such a web a coating system to lead along.

When coating, the casting composition is immersed, Extrusion, cascade or similar processes on a continuously moving web which is on the back by a so-called back-up roller is worn, applied on one side.

The ratio of the wet coating composition applied per unit surface area of the web depends on the web speed especially when the casting composition must be stretched in a coating device, in which the web speed is greater than the feed speed the composition.

In the manufacture of photographic photosensitive The material is the regulation of the web speed at the benchmarking point of great importance. For this reason, the web speed in the modern photographic coating machines is becoming slower is no longer regulated by driven rollers arranged in front of and behind the support roller, it is on the contrary, the back-up roller itself is driven. The back-up roll

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is driven by a motor that runs directly on one end of the shaft the roller is mounted. This motor has high torque and low inertia like a printed motor. Fluctuations in the web speed due to the fluttering of the web in the drying room, the sticking of a fresh web to the running one Trajectory, etc. can be corrected almost immediately by such a drive system.

By using the known devices for measuring the speed of rotation of a roller, it is not possible to have the advantages to fully exploit the drive system described, because the response of these devices is too slow. The usual devices contain a disc that is attached to its circumference equally large light-absorbing and translucent areas is provided, and is arranged on the shaft end of the roller to be measured. There is a built-in measuring head above the disc Incandescent lamp and photocell have been arranged so that the successive points of the disc generate pulses, their Frequency is a measure of the rotational speed to be measured. These devices have the following disadvantages.

The pulse-generating elements of the disc must have exactly the same characteristics because of the smallest difference can affect the registered pulse frequency so that it is no longer a measure of the speed to be measured represents.

It can be due to parallax or an imprecise setup of the measuring head with respect to the disk, errors easily occur, and therefore the free distance between the pane and the photocell or between the pane and of the lamp is usually not a few tenths of a millimeter.

The pulse repetition frequency has to be converted into an analog value which is an instruction for the speed of rotation of the roller is. Indeed, this conversion represents the main disadvantage

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of the "known devices, because the period of the measurement signal becomes too big.

For example, a disk that rotates at 1 rev / sec and is provided with 1000 opaque strips on a transparent base generates a frequency of 1000 Hz, which corresponds to a pulse period of 1 msec. Since the signal has a 100% ripple, it has to be electronically smoothed by an RC circuit (resistor-capacitor circuit) so that it only contains about 1% ripple at the end. This ripple component is reached after only 50 pulses, so that the time constant r of the system is 328 msec ( _r = 2 jf = 6.28 χ 50).

It is possible to achieve short time constants by using what is known as the "phase lock system". at this system becomes the highest for the pulse-generating element Precision is required and, moreover, a very complicated electronic wiring is necessary because the phase measurement with a frequency measurement must be coupled, and consequently an electronic arrangement with very special transmission functions is obtained.

The present invention aims at a method for regulating the speed of rotation of a roller with a short response time, which enables optimal use of the advantages of modern drive motors with high torque.

Another object of the invention is to provide an improved control device, the pulse-generating element of which is not restricted Is tolerance-bound and its arrangement is not critical.

Finally, this invention aims to provide one Control device that does not require complicated electronic wiring.

According to the present invention, the method includes Regulation of the rotational speed of a roller measuring the

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Speed of rotation of this roller, the comparison of the measured value with a nominal value of the rotation speed, the supply of the deviation between the two signals to a controller, which controls a motor driving this roller, and the measurement of the rotation speed of this roller by means of an element that moves synchronously with this roller and is provided with a plurality of pulse-generating elements, two detectors being arranged at fixed locations so that they are excited one after the other and cause the successive signal pulses to be generated by the movement of these pulse-generating elements, and the time periods between the successive ßignalimpuls compared with the setpoint of the Γ rotation speed can be used.

The term "role" should be interpreted broadly enough. It also includes rotatable elements such as a one about a horizontal axis rotatable wheel capable of supporting a track with only part of its circumference, one about a vertical axis rotatable disc with a load bearing capacity on its upper surface, etc.

The device according to the invention for regulating the rotational speed a motor driven roller contains a regulator that controls the electrical current of the motor driving the roller regulates, a comparison knife for comparing the target value of the rotational speed with the measured rotational speed and for feeding the difference between the two values to the controller, and means for determining the measured rotational speed. These means contain a device with various pulse-generating elements, an electromagnetic one Radiation source with which a lot of energy is supplied to the device, two radiation-sensitive detectors, the depending on the direction of movement of the device are arranged with a gap and their radiation-sensitive surface facing a point of the device on which the radiant energy impinges, as well as means for determining the time

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span, which runs between the moment in which a point of the pulse edge passes through the first detector of the device is detected, and the moment at which this point is detected by the second detector.

Preferred embodiments of the device according to the invention are the following.

The device contains means for determining the reciprocal value of said period of time.

The device has multiple pulse generating elements. the shape of a transparent disk, which is provided with several radiation-absorbing fields in the vicinity of its circumference is.

The two detectors are equidistant from the center of rotation the disc arranged. This is the real circumferential speed of a pulse flank of a pulse disc measured on the circumference of a circle, the center of which coincides with the center of rotation of the pulse disc. Of the The advantage of such a measurement is to be seen in its independence from the centering of the pulse disk.

The invention will now be described in more detail with reference to the accompanying drawings, for example in which mean :

FIG. 1 is a block diagram of the control device according to the invention.

Figure 2 is a schematic representation of a coating station.

Figure 3 is a plan view of the means for determining the speed of rotation a role.

Figure 4 is a front view of the pulse disc of the assembly of Figure 3

Figure 5 is another embodiment of the optical assembly according to the figure 3

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Figure 6 is a further embodiment of this optical

Arrangement.
Figure 7 shows three electrical signals that

Explain proper procedures. Figure 8 is a diagram showing the relationship between a

Variable and their reciprocal is represented. Figure 9 is an electronic circuit for determining the Time span, and

FIG. 10 is an electronic circuit for determining the reciprocal value of the output signal of the circuit of Figure 9

According to the block diagram according to Figure 1, a rotatable Roller 70 driven by a high torque motor 71. The speed of rotation of the roller 70 is determined by means of an impulse disc 72, a measuring head 73 and an electronic Circuit 7 ^ · which is the reciprocal of the time between successive Pulses determined by the movement of a pulse edge of the disk in front of the two detectors in the Measuring head 73 are generated, measured. The reciprocal value represents the measured speed value ν and is used in a comparison circuit 75 with the target speed value ν, the is set in a circuit 76, compared. That through the comparison circuit determined deviation or error signal is fed to the controller 77, which the current of the motor 71 regulates to the desired speed of rotation of the roller to adjust.

The roller 70 can be the support roller in a dip coating system, as shown schematically in FIG. 2, in which a web 78 to be coated is drawn over a loose roller 79 and is moved around a substantial peripheral part of the support roller. The web is in the casting composition of the Tray 80 is immersed and is pulled over another roller 81 to a drying station, a second drying station, etc. Known means are used to reduce the tension

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to regulate the web, so that the frictional contact between the The back of the web 70 and the roller 70 is sufficiently large, to let the roller 70 regulate the web speed.

More details about the location of the pulse disc and of the measuring head can be found in Figure 3- The shaft 10 of the roller 70 (the drive motor is not shown in the figure) carries the pulse disk 72, which is provided with optically transparent and opaque fields alternately on its circumference. At one side of the pulse disc are two photocells 12 and 13 in a holder 15 which is mounted in the measuring head 73.

Located between the pulse disc 72 and the photocells 12 and 13 a screen 14, which has two slits at the location of the photocells. For photocells 12 and 13 is it is important to be located at exactly the same distance from the axis of rotation of the pulse disk 72. This means righteous that the center of the disk must coincide with the axis of rotation of this disk, and consequently the disk does not need to to be precisely centered with respect to shaft 10.

On the other side of the pulse disk 72 is a light source 16 and an optical pilaster system 17? the one almost parallel light beam is directed onto the pane at the location of the photocells 12 and 13.

The number 18 in the arrangement of FIG. 3 relates to the light spot projected by the optical system I7 and is detailed in Figure 4-.

Examples of usable photocells are photoelectric transistors such as the LS-400 from Texas Instruments or the MRD 200 from Motorola (trade names). The diameter of this photoelectric transistors is approximately 2.5 mm, which limits the minimum pulse spacing on the disc. This However, the distance can be reduced if an optical system 69 is used for reading out, which is directed to the photocells an enlarged image of the flanks is projected (Figure 5)

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This optical system must provide a very faithful reproduction, because otherwise it will cause measurement errors. Another readout technique involves the use of light conducting elements e.g. optical fibers 68 and 67 * which the picture after photocells transmit, e.g., photomultiplier tubes 40 and 41 (Fig. 6).

The pulse-generating elements or windows can, for example, be arranged on a dimensionally stable and highly impact-resistant glass pane on which a hard gradation photographic emulsion in the form of a layer about 10 µm thick was coated became. The windows are formed on the pane, e.g. by taking successive slit-shaped flash exposures, while this disc is rotatably mounted on the distributor head of a milling machine.

Thanks to the insensitivity of the measuring system to a sequence irregular pulses along the circumference, the resulting accuracy will usually be sufficient.

Instead of photographic impulses, you can also use mechanical disks Manufacture pulse disks, i.e. pulse disks with mechanical interrupted wall parts. The quality of the latter slices, however, is due to an insufficiently abrupt transition from signaling often unsatisfactory in a non-signaling state. Usually there is a diffuse light scattering the relatively thick, crenellated walls. In comparison, the low layer thickness of photographic materials represents represents a significant advantage in that it allows very steep pulse edges.

The measurement of the time span between the detection of one and the same edge by both photocells is electronically done by spei nt an integrator with a constant input voltage during this period. The final voltage of the integrator is then directly proportional to this time span. This voltage can be stored in a memory

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can be entered so that at the end of the measuring time an exact value of the time span is available.

In FIG. 7, the current pulse 30, the integrator voltage 31 and the voltage 32 registered in a memory are illustrated.

In most cases, the angular velocity value of the disk or the element to be measured is of the greatest importance. This angular velocity is inversely proportional to the pulse period. For the electrical determination of the reciprocal value of a There are several known methods of tension. If you only intend a narrow speed range, you can use the tangent at a certain point to the hyperbola, which shows the relation of a variable E. to its inverse

value Ep = ψ- results. Pig. Fig. 8 shows the curve showing the relationship of E ^ to E £.

If you want a larger speed range, you can use non-linear techniques for converting the hyperbola Referring to Fig. 8 in a straight line, e.g. the "use of diode circuits, their attenuation of the applied voltage is inversely proportional. This method can be made to work very precisely, but it requires a lot of regular work. For this reason, it is mostly preferred to do the actual division without further ado.

In Fig. 9, an electrical circuit for measuring the pulse period is shown. The output signals of the photocells 12 and 13 are connected to triggers 50 "and 51, respectively. The output signals the trigger regulate a flip-flop 52, which the One after the other an integrator 53 regulates. At the end of the measurement period, a monostable multivibrator 57 creates a Pattern and hold circuit 5 ^ started, so a new one Measuring cycle can begin.

The output signal E ^ of the circuit of FIG. 9 is the period directly proportional. So their reciprocal values have to be determined

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will. An electronic dividing circuit is used for this, which is based on the division of time by modulating the pulse width.

Let E ^ be the output voltage of the circuit of FIG Reciprocal value is to be determined. The width of the pulses of a pulse train e- with a sufficiently high frequency is modulated with E ^ so that E ^, = ka, where α is the on / off ratio of the pulse train e- is.

The feedback current of an operational amplifier 60 shown in FIG. 10 is modulated by means of the pulse sequence e-. A capacitor C is connected between the input and the output of the amplifier 60, and a resistor can also be connected via an amplifier by means of a switch 61 which is _{regulated by the pulse train β Ί} ·. The output voltage of the amplifier 60 is E ₂ = R _e ffi> where i_ denotes the input current of the amplifier and R _f ^ denotes the effective feedback resistance. However, it is Ep = Ri ¹ , where i_ is the current value through R when switch 61 is closed, and i ¹ = i, since no charge can be accumulated in capacitor C under steady-state conditions. Furthermore i '= α i', so that E ₀ = Ri '= ^ fi' = ^ i = R ik. ψ-

a α ±> s \

If i_ is kept constant, the circuit of FIG. 10 as a dividing device, the signal Ep with the Signal ν according to FIG. 1 coincides. The output ripple is determined by the modulation frequency and the time

CR
constant through - given.

A magnetic dividing device (the so-called Hall effect) or use a logarithmic or other fast dividing device.

In an embodiment according to the invention, the diameter amounts to a glass pulse disc to 50 cm, its thickness 3 mm, while its circumference with 600 narrow black fields

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was provided. The space between the logs and the Lamp, and between the disc and the photocell of the measuring head "amounted to 7 π & - It has been shown that the disc around 1 mm could be mounted off-center and the flutter deflection of the disk could be 2 mm and that nevertheless a control accuracy of 1/1000 for speeds of 0.1 to 10 rpm.

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Claims (10)

Expectations ^r 1Λ Method for regulating the rotational speed of a roller by measuring the rotational speed of this roller, comparing the measured value with the nominal value of the rotational speed, supplying the deviation between the two signals to a controller that regulates the drive motor of this roller, measuring the rotational speed of this roller takes place by means of an element which moves synchronously with this roller and is provided with several pulse-generating elements, characterized in that two detectors are arranged at fixed points so that they are excited one after the other by movement of these pulse-generating elements and cause successive signal pulses, and that the time span between the successive signal pulses is used in the comparison with the nominal value of the rotational speed. 2. The method according to claim 1, characterized in that when the pulse-generating element passes a fixed point, the edge of the generated pulse is detected by a detector, the same edge of another pulse, generated when passing a second fixed point through this element, detected by a second detector and the time between the instants in which these pulse edges are detected by these detectors is used when comparing with the target value of the rotation speed. 3- The method according to claim Λ or 2, characterized in that the reciprocal value of this time period is determined. 4. Device for regulating the speed of rotation of a roller driven by a motor, which has a regulator for the electrical Current of the drive motor, a controller for comparison 209819/0631 of the setpoint speed value with a measured speed swert and to supply the difference between these "two values to the controller and means for determining the contains measured speed values, characterized in that these means comprise a device with several pulse-generating elements, an electromagnetic one Radiation source with which a lot of energy is supplied to the device, two radiation-sensitive detectors, which are arranged according to the direction of movement of the device with a gap and their radiation-sensitive Surface facing a point of the device on which the radiant energy impinges and Contains means for determining the period of time which passes between the moment in which a point a Pulse edge is detected by the first detector of the device, and the moment at which this point through the second detector is detected. 5 · Device according to claim 4-, characterized in that the device has the shape of a transparent disk, which is in the vicinity of its perimeter with several radiation absorbers Fields is provided. 6. Device according to claims 4 and 5? characterized, that both detectors are arranged at the same distance from the center of rotation of the disk. 7. Apparatus according to claim 4, characterized in that it Contains means for determining the reciprocal of the period of time. 8. Device according to one of claims 5-7? characterized, that the electromagnetic radiation source is a light source, and that between the disc and the detectors an optical magnification system is arranged. GV.5O6 209819/0631 9 · Device according to one of claims 5-7> characterized in that
that light guides are arranged between the disc and the detectors. 10. Photographic web of paper or film, their speed has been regulated in the production according to the method according to claims 1-3. 209819/0631