EP0038054B2 - Apparatus for the automatic regulation of a roller mill comprising a product-feed control - Google Patents

Abstract

According to the method, a mechanical control signal is generated according to the product supply for the control of a metering valve (9). To obtain powerful control operation with a high precision and reliability and of a simple and compact construction, the mechanical control signal is first transformed into a pneumatic signal which is transmitted as an input signal to a servocontrol (41) for regulating the product supply and/or to a servocontrol (18) for the start up or shut down of the milling cylinder. A device specially adapted to this method is a cylinder mill which comprises a mechanical signal transmitter (13, 15) operating a pneumatic regulating valve (17) of which the output is connected to the input of a servocontrol (18) actuating the metering valve (9) and/or the start up and shut down of milling cylinders (1, l', 2, 2').

Description

adjustable metering slide is carried out, a mechanical signal transmitter depending on the product supply deflects a transmitter element which actuates a switch contact which can be pressed into a pneumatic valve and which is pressed in by the transmitter element when the product supply increases, the input of the valve being connected to a compressed air line and for adjustment of the metering slide a servo device is provided.

In CH-A 418791 a milling roller mill is described, the performance-dependent elements of which are controlled via a central electrocapacitive feed quantity measuring device, by means of which the presence of a sufficient product depot in the dining area is ascertained via a feed roller and corresponding electrical control signals at electropneumatic valves for control and. a. be given the position of a metering slide. In the case of particularly difficult products, however, this shows that the regulation of the feed power is not always completely harmonized because the product can stick to the capacitive probe, which makes fine adjustment difficult.

DE-C 582423 describes a combination of electrical and mechanical control means which are also suitable for use with larger control forces, but the structural outlay is very considerable, in particular due to the use of a mechanical and an electrical system.

In the arrangement from DE-C 817069, the mechanical output signal is used directly to control a downstream servo motor, with the mechanical transmitter element acting directly on the on / off control valve on the housing of the servo motor. Depending on the deflection of the mechanical encoder element due to the load, the servo motor directly actuates the metering slide via its output and an intermediate gear reduction. Fluctuations in the supply of the product result in corresponding fluctuations in the metering control.

Finally, CH-A 275417 describes a control arrangement of the type mentioned at the outset, in which, depending on the product supply, the mechanical encoder member is deflected and actuates a control pin of a pneumatic cylinder. The housing of the pneumatic cylinder is rigidly attached to the roller frame, and the displacement movement of the piston of the pneumatic cylinder triggered by the control pin depending on the deflection of the encoder member is in turn used directly via intermediate levers to adjust the metering slide.

Proceeding from this, the object on which the invention is based is to further develop a device of the type mentioned at the outset in such a way that, with a relatively simple structure and little effort, it enables a particularly constant product feed and a particularly good maintenance of the product level even in the event of large fluctuations in performance.

According to the invention, this object is achieved in a device of the type mentioned in the introduction in that the output of the pneumatic valve is connected to the input of the servo device via a control line, the pneumatic valve in an off position, in which the switch contact is in the extended position, and in a switch-on position, in which the switch contact is fully depressed, and switchable into a zero position between the two switch positions, in which the switch contact is in a middle press-in position and both lines are blocked, the switch contact when pressed in the direction of its extended position is preloaded, and that during an adjustment movement of the servo device, the housing of the pneumatic valve is always moved relative to the transmitter element in the direction of setting its zero position. The invention makes it possible, with a mechanical signal transmitter, to regulate the product feed for a roller mill sensitively via a servo device by means of a follow-up control using a valve with an intermediate zero switching position. The use of a three-position valve, which is required according to the invention and which follows every movement of the transmitter element with a delay, leads, as practice shows, to a regulation in which a really constant product supply line and an excellent constant level of the product level in the dining area, even in the case of strong short-term ones Shock loads in the product feed can be achieved.

An advantageous embodiment of the device according to the invention also consists in that a second valve, acted upon by the control pressure in the control line of the pneumatic valve, is provided for controlling the engagement and disengagement of grinding rollers.

A particularly simple construction of an effective and reliable design of the device according to the invention is achieved in that a lever arm is attached with its one end pivotable to the roller frame, on which both the housing of the pneumatic valve and an adjusting member for the metering slide as well as the piston rod also are provided servo devices arranged on the roller mill frame, the housing of the pneumatic valve being seated at the free end of the lever arm, the servo device further comprising a pneumatic cylinder with piston and piston rod, and the control side of the piston being acted upon by the control pressure of the pneumatic valve via the control line, while the other side of the piston is under the influence of a preload. In this embodiment, the servo device forms together with the lever articulated on one side on the roller mill poor a functional unit in which effective and reliable control of the feed power is possible with just a few moving parts. The structural effort required is surprisingly low. It is advantageous if links for adjusting the speed of the feed rollers are also attached to the lever arm, wherein regulation of the feed power is possible alternatively or simultaneously by means of a metering slide on the one hand and feed roller speed on the other.

A particularly advantageous embodiment of the device according to the invention also consists in the pneumatic valve being designed as a diaphragm valve which is switched by a tappet or a roller lever which has a vent opening. The piston side facing away from the control side of the piston for adjusting the metering slide is preferably biased by a compression spring in the direction of a closed position of the metering slide.

The application of the device according to the invention in practice has shown that with a uniform product supply, the product level in the dining area above the metering rollers also remained constant. Furthermore, it has been shown that even if very strong power fluctuations occurred, the metering power was optimally adapted to these power fluctuations by the arrangement according to the invention, with a strong smoothing being achieved at the same time in the control behavior. It has always been shown that the functional reliability was extremely high.

• Figur 1 eine schematisch dargestellte Ausführungsform für eine erfindungsgemässe Steuerungsanordnung;
• Figur 2 und Figur 3 den gemessenen Druckverlauf eines pneumatischen Regelsignales zu einer Ausführung gemäss Figur 1;
• Figur 4 ein vollständiges Steuerschema bei einer erfindungsgemässen Anordnung an einem Müllerei-Walzenstuhl mit Speiseregulierung, kombiniert mit automatischer Walzenein- und -Ausrückung;

The invention is explained in more detail below in principle by way of example with reference to the drawings. Show it:

• Figure 1 is a schematically illustrated embodiment for a control arrangement according to the invention;
• Figure 2 and Figure 3 shows the measured pressure curve of a pneumatic control signal for an embodiment according to Figure 1;
• FIG. 4 shows a complete control diagram in the case of an arrangement according to the invention on a milling roller mill with feed regulation, combined with automatic roller engagement and disengagement;

A product feed control is shown schematically in FIG. 1: in the left half of the figure, the feed area 70 is shown, which is closed at the bottom by a distribution roller 71, a feed roller 72 and a metering slide 73. A probe 74 is arranged in the dining area 70 and is supported on a pivot pin 76 by a support 75. The carrier 75 has a transmitter 77 which is operatively connected on the one hand to a tension spring 78 and on the other hand to a roller lever 79 of a pneumatic valve 80. The pneumatic valve 80 is connected on the input side to a compressed air line 81; a control line 82 leads from the pneumatic valve 80 to a servo cylinder 83 to act on a piston 84 located therein on one side thereof. Furthermore, a piston rod 85 is provided, which is fastened at the end with a hinge pin 86 to a lever arm 87, which in turn is articulated on the fixed frame structure 89 about a swivel joint 88. The pneumatic valve is fastened to the other end of the lever arm 87 and follows the lever laws, the movement of the piston rod 85 and the lever arm 87. A metering slide 73 is also non-positively fastened to the latter via a connecting bracket 91 or planks 92 and 93. The metering slide 73 can be tilted about a pivot bearing 94, a metering gap being established between it and the feed roller 72, depending on its current position. The entire system is fed by a pressure supply 95.

The compressed air for the control side can also be interrupted via a hand switch 98, for example to carry out service work. The system pressure is kept constantly at a constant pressure by the supply mentioned, which pressure (e.g. at a value of 6 bar) is delivered via a line 99 as a counterpressure to the side of the piston 84 which is away from the control pressure. Instead of the constant pressure mentioned via line 99, a spring 100 or both can also be used together. The use of a spring 100 has the advantage that the metering slide closes securely if the compressed air fails.

FIG. 2 shows the pressure curve of the control signal, as can be determined in the control line 82 using a pressure recorder. The values correspond to the measurement on a roller mill of a B passage. During a first phase of about 50 seconds, the pressure is remarkably stable and only briefly (at about 29 seconds) is interrupted by a short pressure increase. The essentially horizontal course of the curve shows that very short-term power variations are passed on in the control signal. At approx. 50 seconds, the entire control loop is artificially interrupted by manually disengaging the grinding rollers, which means that the control signal immediately drops to zero. The rapid response of the control to a corresponding malfunction is very advantageous. However, it is particularly important to start the control after the grinding rollers are engaged. According to the measurement of the pressure recorder, the control signal runs out for about 1 sec. The restart of the signal occurs almost without delay and, which is particularly interesting from a control point of view, the signal immediately goes to an approximately medium value, then swings for about 10 seconds this value and then immediately leads back to a stable control behavior. Particularly noteworthy is the quick reaction to the change, which takes place with almost no oversteer and no rocking.

FIG. 2 shows constantly recurring constant control periods of 5 to 10 seconds, all of which lie within a relatively narrow control range. For the grinding rollers and this is very important for the roller bearing, since it can be prevented by the feed control device from vibrating due to constantly changing grinding forces.

In Figure 3, the control signal is shown for a C passage (i.e. a rear passage) in which the amount of product fed to the roll mill hardly varies over shorter and longer periods. This case is particularly easy to control in terms of control technology. About 5 seconds after the start of the measurement, the product supply was briefly disrupted, which immediately triggered a corresponding drop in the control signal. In terms of control technology, the curve curve that follows is almost a kind of “ideal curve”. In this case too, the grinding rollers were briefly removed by hand after about 115 seconds and then immediately reinserted without delay. The diagram shown shows, surprisingly, that after a very slight override, the same control value as before the artificial disturbance is restored after about 1 to 2 seconds and the original curve continues.

FIG. 4 shows an embodiment in which the feed regulation shown essentially in FIG. 1 is combined with a roller engagement and disengagement.

FIG. 4 shows an embodiment for a typical mill roller mill with a double design for the actual grinding unit.

By means of a central control valve 96, all the rollers Wa ₁ , Wa ₂ ... can be disengaged with the aid of the quick breather 97.

The piston 120 is coupled to the movable roller or the corresponding roller bearing via a piston rod 121.

In addition, however, it is also shown that the servo cylinder for the roller engagement and disengagement is provided at each roller end, ie a total of 4 times.

The operation of a mill mill according to one of the exemplary embodiments shown corresponding to Figures 1 to 4 is as follows:

The grinding gap of the grinding rollers is selected according to the material to be ground using a handwheel. If no regrind is being fed in via the dining area 70, the probe 74 is pressed upwards by a tension spring 78. The transmitter 77 does not touch the switch contact 79 of the pneumatic valve 80, so that no pressure is built up in the control line 82. The spring 100 or the pressure from the line 99 (or both, depending on the choice of system) push the lever arm 87 counterclockwise and thus the metering slide 73 into a closed position. The metering gap is closed so that no product is metered onto the grinding rollers. If there is no control signal in the control line 82 or 115, there is also no control pressure at the booster valve 116, which is why the grinding rollers are in the disengaged position via the cylinders 118.

If ground material is now fed to the roller mill via the dining area 70, the impulse of the flowing material or a corresponding weight component acts immediately on the probe 74, which is thereby pressed downwards. The encoder 77 moves to the right, presses in the switch contact 79, and thereby triggers a control signal.

A pressure now builds up in the control line 82, but this initially does not cause any change in the signaling. However, as soon as the pressure has reached a set threshold, the grinding rollers are engaged. This is a dynamic process. The probe 74 is in motion with the transmitter 77, i. H. the switch contact 79 is fully pressed onto the pneumatic valve 80 in one go. The transmitter 77 releases the maximum control pressure in the control line 82 even with the smallest movements, particularly when using a very sensitive diaphragm valve for the pneumatic valve 80. As a result, the piston rod 85 with the lever 87 and the pneumatic valve 80 are set in motion in a period of hundredths or tenths of a second, with the directly connected metering slide starting to open and product being fed onto the grinding rollers. Both the cylinder 118 and the cylinder 83 are designed as pneumatic servo cylinders, as a result of which the workforce is generated quickly but not suddenly. In contrast to hydraulic media, the air in the cylinder forms a kind of “shock absorber”. It has been shown that a suitable choice of the tension and compression springs of the cross-sections in the pneumatic lines and corresponding preloads of the springs can achieve a perfect synchronization of the control functions with regard to the machine elements concerned. This applies to both the entry and exit cases.

For the further sequence of movements, reference is made to FIGS. 1 and 4: the lever arm 87 executes a small swiveling movement clockwise when the product feed is inserted as the first phase. Simultaneously with this, the switching contact 79 also runs away from the transmitter 77. The tension spring 78 tensions in proportion to the distance of the encoder 77. If only a small amount of product is fed in via the glass cylinder, then a balance is established very quickly between the regrind forces on the probe 74, in which the feed segment 73, the lever arm 87 and the pneumatic one Valve 80 remain in position. At the same time, however, the transmitter 77 and the switching contact 79, which can be inserted into the pneumatic valve 80 via a spring, are in constant mutual interaction, whereby the smallest movements occur, which, however, which is a significant advantage, no longer have a direct influence on the changed. exert pneumatic control signal. The pneumatic valve 80 remains in this phase in a zero position, with all on and off aisles are closed. As a result, the pressure value of the pneumatic control signal generated in the first phase remains unchanged and the piston 84 is rigidly clamped by relatively large forces due to the stable pressure conditions on both piston sides. The metering slide 73 remains quietly in its position. If the supply of the goods is now increased or the power supplied in the dining room is greater than the power discharged through the metering gap for other reasons, the transmitter 77 continues to move in the direction of the switching contact 79 or on the pneumatic valve 80, the latter being the transmitter 77 runs on and, at a set threshold value, again emits a corresponding control signal as an increased pressure value in the control line 82. Depending on the circumstances, e.g. also when it comes to a start-up process or the like. acts, a pneumatic control signal is predetermined or triggered approximately according to FIG. 2 or FIG. 3. Depending on the precondition, a stable equilibrium can be established over a uniform signal curve, as can be seen from FIG. 3. However, even with constantly fluctuating feed rates, individual periods of stable positions, in which the pneumatic valve 80 is located at any point on the lever arm 87, can alternate in the zero position. The control shown is thus able either to generate a very uniform control signal (see FIG. 3) or, if the supply power is very variable, to have a signal of repeatedly stable phases (see FIG. 2).

As can be seen from FIG. 4, the control pressure in line 119 can be used for the optical display of the respective position of the rollers. With compressed air e.g. a colored buckle can be moved behind a glass eye 120, so that the engagement or disengagement of the grinding rollers by appropriate colors, for. B. red and green, is displayed.

Furthermore, the pneumatic control signal in the control line 82 can also be used to set the grinding rollers independently of the power. For example, the grinding gap can be kept constant when the metering capacity is increased by increasing the grinding pressure, or it can also be reduced or enlarged. A corresponding grinding gap control device can consist directly of a pneumatic cylinder or other suitable mechanical or electrical means, which can also be connected to a remote control (such as a computer or process computer), which then specifies a basic value for the respective grinding task, which Depending on the output, the pneumatic control signal adjusts the instantaneous output in the roller mill. It goes without saying that other training courses can also be carried out here or other functions can be carried out, e.g. B. with regard to the limit value, with regard to safety circuits, etc. Particularly advantageously, it can also be controlled as a function of the feed power or by means of the pneumatic control signal. It is also noteworthy that the pneumatic control signal can be used to control both the feed rate and the engagement and disengagement of the grinding rollers.

Claims (6)

1. A system for automatically controlling a milling roll stand having product feed control, product feed being adjusted through the agency of an adjustable dispenser (73), a mechanical detector or sensor (74-77) deflecting an element (77) thereof in dependence upon product feed, the element (77) operating an actuating contact (79) adapted to be pressed into a pneumatic valve (80), the latter contact (79) being pressed in by the detector element (77) as product feed increases, the input of the valve (80) being connected to a compressed air line (81), a servo device (83) being provided to adjust the dispenser (73), characterised in that the outlet of the pneumatic valve (80) is connected by way of a control line (82) to the input of the servo device (83); the pneumatic valve (80) can take up an "off" position, in which the contact (79) is in its extended position, an "on" position, in which the contact (79) is in its fully pressed-in position, in which the contact (79) is in its fully pressed-in position, and a neutral position which is disposed between the "off" and "on" positions and in which the contact (79) is in a middle pressed-in position and the two lines (81, 82) are in the closed state, the contact (79) being biased towards its extended position when pressed in; and when the servo device (83) makes an adjusting movement, the casing of the pneumatic valve (80) moves continuously towards an adjustment of its zero position relatively to the detector element (77).

2. A system according to claim 1, characterised in that a second valve (116) actuated by the control pressure in the control line (82) of the pneumatic valve (80) is provided to control the engagement and disengagement of milling rolls (1, 1 1; 2,21).

3. A system according to claim 1 or 2, characterised in that a lever arm (87) secured pivotally at one end to the frame (89) of the milling roll stand is provided and has secured to it the casing of the pneumatic valve (80) an adjusting element (91) for the dispenser (93), and the piston rod (85; 121) of the servo device (83; 116, 118), the same also being disposed on the last-mentioned frame (89), the casing of the pneumatic valve (80) being disposed at the free end of the lever arm (87); the servo device has a pneumatic cylinder (83; 118) associated with a piston (84; 120) and a piston rod (85; 121); and the piston (84; 120) has its control side acted on by way of the control line (82) with the control pressure of the pneumatic valve (80) and its other side acted on by a biasing force (99, 100).

4. A system according to claim 3, characterised in that members for adjusting the speed of the feed rolls (71, 72) are secured to the lever arm (87).

5. A system according to any of claims 1 to 4, characterised in that the pneumatic valve is a diaphragm valve actuated by a tappet or a cam follower lever having an airvent opening.

6. A system according to claim 3 or 4, characterised in that the piston side remote from the control side of the dispenser-adjusting piston (84; 120) is biased by way of a compression spring (100) towards a closed position of the dispenser (73).

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