The present invention relates to an apparatus for the dynamic correction of the angular position of a driven roll. Apparatus of this kind is used primarily in the printing trade. Rolls which require angular correction can be found in several different units along a printing press line, e.g. at the infeeder, at the cooling roll position, at line index apparatus and at other places.

The present invention relates to an apparatus for dynamic control of the angular position and/or the angular velocity of a driven roll. Apparatus of this kind is primarily used in the printing trade and within process industry, e.g. in plastics extrusion.

Rolls requiring their angular positions and/or velocity to be controlled can be present in several different sub-processes along a printing press line, e.g. at the infeeder, at the cooling roll position, at the line registers in the printing section and in other places.

The task of the cooling roll is to cool the paper web which has been heated in a drying oven. Another task is to control the feed velocity of the paper web so that optimum web tension is obtained in the drying section and at the cooling roll.

Between the cooling roll position and the folding section, there is a folding index. The index comprises one or more movable rolls, the mutual positions of which can be controlled manually or automatically for adjusting the paper position relative the folding section.

A normal requirement for the cutting-off accuracy of the folding section is +0.2 mm. A fault in the cooling roll position directly affects the accuracy in the folding section. The requirement for positional accuracy at the cooling roll is therefore just as high. Let is be assumed that the circum¬ ference of the cooling roll is 1000 mm. The mentioned require¬ ment would then signify that a control accuracy of 0.2 permille

is needed at the cooling roll position.

The cooling roll position is usually driven from a cardan Shaft common to the entire press line, driving power being taken off from the shaft with the aid of angular gearing and toothed belt to a gearbox. Correction revolutions controlled by a motor and an infinitely variable gearbox (alternatively an electronically controlled motor) are supplied to a second input shaft on this gearbox. The two input revolutions are added in a differential gear of the type which has a great reduction ratio. The corrected revolutionary rate on the output shaft of the gear box is taken with the aid of a toothed belt or spur gear to the cooling roll shaft. The large number of transmission elements here give rise to superposed disturbance and easily cause a plurality of un¬ favourable natural resonances in the system.

As mentioned above in the example with the cooler roll control, the control requirement is 0.2 permille. The main power supplied to the cooler roll position is 1-5 kW. An alternative is to drive the cooler roll position directly, without being dependent on a cardan shaft. This however, requires very sophisticated motor control, if possible at all with today's technology. Normal motor controls in these power classes generally only promise a control accuracy of 0.5 %.

The object of the invention is to achieve an apparatus which allows dynamic control of the angular position and/or the angular velocity of a driven shaft with a control accuracy of less than a few permilles. Another object is to achieve this control with the aid of transmission elements rigidly connected to each other to form a unit mounted directly on the shaft which is to have its angular position and/or its angular velocity controlled.

In accordance with the invention, the above-mentioned objects are achieved with an apparatus of the kind disclosed in the claims. In relation to the state of the art, the apparatus,

which comprises motor, gearing and angle transducer/tachometer, affords the advantage that it is placed directly on the shaft end of the roll or cylinder it is to control. The output shaft of the differential gear is thus directly connected to the roll without any further transmission elements, the mechanical imperfections of which can affect the control. The gear is of the type described in my previous patent application PCT/SE88/00027 and has properties which are important in the present application, namely low inertia on the input shaft, freedom from play and high rigidity.

In accordance with the present invention, the known gear has been modified and utilised as a differential gear, mounted on its output shaft. The gear housing is exteriorly provided with . a toothed ring to which the incoming main power is transferred by a toothed belt. The second input shaft to the differential gear comprises the ^■• normal" input shaft of the gear. A control motor is connected to this "normal" input shaft for supplying correction revolutions.

An angle transducer or tachometer is connected directly to the load (the roll). For obtaining a compact servo unit which is easily exchangeable, the angle transducer/tachometer is placed in the end wall of the motor. The angle transducer/- tachometer shaft is directly connected to the output shaft of the servo unit by the motor and gear having a through bore with clearance for the long shaft of the angle transducer/- tachometer. This is .an advantage in such as cooling rolls, where both shaft ends must not be blocked.

Using a toothed belt as the final step in the transmission of the main power to the servo unit, there is obtained a certain filtration of high-frequency disturbances. With its large mass the roll has high inertia. The use of a toothed belt drive affords a dynamic system with relatively low natural frequency. The toothed belt can be likened to a lowpass filter. By the combination of motor-gear-angle transducer/- tachometer there is obtained a servo system with a high

roll off frequency which gives very accurate control of the roll.

In certain applications, it is perhaps preferable to use a spur .gear transmission instead of toothed belts. The servo roll off. frequency, which can be increased up to a relatively high value by increasing the revolution rate, will then put a limit to the accuracy of the system with respect to position- al and revolutionary rate.

The invention will now be described in more detail and in connection with the accompanying drawings, where

Figure 1 is an exploded sectional view of the apparatus in accordance with the invention,

Figure 2 is a side view, partially in section, of the ap¬ paratus in accordance with the invention, and

Figure 3 is a sectional view of the gear now functioning as a differential gear with the aid of which the revolu¬ tionary rate of the driven roll is corrected.

Figure 1 illustrates a roll frame 2 in which a roll 2 with a shaft 3 is mounted with the aid of bearings 4 and 5. One end of the shaft 3 has a flange 6, and in Figure 1 the latter is illustrated combined with a toothed wheel 7, the function of which is described in more detail below. A gear is generally denoted by the reference numeral 8, and has the shape of a short cylinder with large diameter. It is of the general type described in my- international patent application PCT/SE88/-

5 ^* 00027. In accordance with the present invention, this known gear is modified so that the surface of the gear housing is provided with external teeth forming a toothed ring 9. In the embodiment according to Figure 1, the toothed ring is adapted to be driven by a,toothed belt, in turn driven by the unil- lustrated main shaft of the printing press. A correction motor 10 with aμ. output shaft 11 is carried by a motor support

12 and a mounting plate 13 on the roll frame 1. The output shaft 11 of the motor is rigidly connected to one input shaft on the gear 8 serving as a differential gear. The other input shaft of the differential gear consists of the toothed ring 9. A conventional type of tachometer 14 has been provided, in accordance with the invention, with an extended shaft 15 which is rigidly connected to the output shaft 16 of the tachometer 14. The extended shaft 15 passes through the motor shaft 11, as well as the gear 8 and is fixed to the output shaft (denoted by 17 in Figure 1) of the gear. This output shaft is adapted to be rigidly connected to the flange 6 on the shaft 3 of the roll 2. The tachometer 14 will accord¬ ingly measure the revolutionary rate of the cylinder.

The output signal from the tachometer is fed to an unil- lustrated control circuit as an actual value for the angular position of the roll 2. A set value for the angular position of the roll is obtained from some other part in the press, e.g. the angular position of a preceding or subsequent roll along the press line. The unillustrated control circuit forms a difference signal which changes the revolutionary rate of the correction motor until the actual valve equals the set values. Such control circuit are known and therefore not described in more detail, since they do not form any part of the present invention.

Figure 2 illustrates the apparatus in Figure 1 in an assembled state. It will be seen from the Figure that the unit formed by tachometer, motor, gear and toothed wheel is a physical unit mounted on one end of the shaft 3. Figure 2 also schemati¬ cally illustrates the case where the roll is a cooling roll, to which cooling water is fed via a sleeve 18, from where the water goes into a cooling cylinder 20 to cool its exterior circumferential surface from the inside, the water departing via a sleeve 19. The sleeves 18 and 19 are here arranged on the side of the roll opposite to the servo unit formed by the tachometer 14, motor 10, gear 8 and the unillustrated elec¬ tronic control circuit. This arrangement is advantageous,

since no fragile components are on the side where the cooling water sleeves are situated. Such sleeves always leak sooner or later, and can damage or otherwise disturb the units included in the servo.

Figure 3 is a cross-section view of the gear and its connection to the correction motor and to the toothed wheel 7 and shaft 3. Figure 3 also illustrates how the extended shaft 15 of the tachometer is fixed to a fixing ring 21 with the aid of a screw 22. With the aid of a screw 23 the fixing ring 21 is in turn screwed to the output shaft 24 of the gear, this shaft having the form of a wheel. The cylindrical housing 25 of the gear 88 carries the toothed ring 9. A ring 26 with internal teeth forming a toothed ring 27 rests against a shoulder 28 in the cylinder housing 25. An eccentrically mounted spur gear 29 rolls in the ring 27. In the preferred embodiment, the ring 27 has only one tooth more than the gear wheel 29. This gear wheel 29 is mounted via a bearing 30 on a sleeve 31, which is eccentrically mounted on a second sleeve 32, which is άn turn eccentrically mounted on the input shaft 33 of the gear. The mutual angular position of the sleeves 31, 32 is fixed. A balancing weight 34 projects out in a radial direction from the sleeve 32 and is made integral therewith. The input shaft 33 of the gear is mounted in bearings 35 and 36. The rotating movement of the gear wheel 29 is transmitted via a transmitter member to the output shaft 24 of the gear. The transmitter member is of the kind described in my interna¬ tional patent application PCT/SE88/00028, and since it does not form any part of the present invention it will therefore not be described in any more detail. It is sufficient to say here that the transfmitter member includes a pivoting stirrup 37 which, with the aid of claws, is in movement transmitting engagement with the gear wheel 29 for transmitting its rotating and translating movement to the output shaft 24. The stirrup 37 is slidably mounted on a shaft 38 rigidly connected to the gear wheel 29 at one end and pivotably mounted at its other end on a pivoting pin 39, about which the stirrup pivots. The gear described so far functions as a differential. One input

shaft of the differential comprises the toothed ring 9 and its other input shaft is the gear input shaft 33, which is also the output shaft of the correction motor 10 in this case. Let it be assumed that the reduction ratio of the gear is 100:1. If the output shaft 24 and thereby the shaft 3 is to rotate at 500 rpm, the correction motor 10 must also rotate at 500 rpm, and the whole differential will then rotate as a unit. However, if the angular position of the cooling roll is incor¬ rect, e.g. it lags by 10°, the correction motor adds a velocity to the output shaft so that it will rotate somewhat faster than the revolutionary rate of the ring 9. Assume that the control circuit increases the speed of the correction motor from 500 rpm to 600 rpm. Since the reduction ratio is 100:1, the output shaft 24 now rotates at 501 rpm. This increased rate is maintained until the lag has been compensated and the shaft 3 assumes the desired angular position. On the other hand, if the shaft 3 has an angular position in advance of the one desribed, the control circuit decreases the velocity of the correction motor from the nominal 500 rpm to (say) 400 rpm. The roll 3 will then rotate at 499 rpm. This lower revolutionary rate is maintained until the control circuit sences that the desired angular position has been reached. The tachometer senses the actual value of the angular position of the shaft the whole time. As mentioned above, the set value of the shaft angular position can be obtained from some other machine compontent or alternatively it can be a fixed predetermined value.

The condition may arise that a disturbance occurs in the operation of the correction motor 10. Its output shaft could then cease to rotate the internally toothed wheel 29 and the revolutionary rate of the shaft 3 would be lowered considerab¬ ly. In order to enable continued operation of the printing press in such circumstances there is a loocking mechanism arranged in the end wall 40 of the gear housing. The mechanism includes an arm 41, at one end of which there is disposed a knob 42 or the like. The arm is fixed in one end of a shaft 42 passing through the end wall 40. A disc 43 is eccentrically

mounted at the other end of the shaft. When the locking mechanism is operated by manually gripping the knob 42 and turning the arm, the eccentrically mounted disc 43 is turned into engagement with the balancing weight 34, which forms a unit with the sleeve 32, this sleeve and the sleeve 31 being rigidly connected to the input shaft 33 by means of a pin 44. In this position of the locking mechanism, the rotational movement of the rotating housing 25 will be transmitted via the disc 43 to the input shaft 33 of the gear. Both input shafts of the differential gear now rotate at the same rate, and the differential rotates as a unit for transmitting the nominal input revolutionary rate to the output shaft 24.

In the illustrated embodiment, an additional V-belt pulley 7 is placed over, a tension sleeve 45, which in turn is placed over the shaft 3. The pulley 7 is rigidly connected to the output shaft 24 by means of screws 46. The pulley 7 may, but not necessarily, be included. With the pulley, the gear is suitable as a master drive unit for other slave driven rolls.

Although the invention above has been described in connection with a cooling roll, it can be used in connection with any driven roll. The invention has also been described as being intended for correcting the angular position of the driving roll, but it will be _^ understood that the revolutionary rate of the driven roll can also be corrected with the aid of the invention.

It will be understood that the gear housing does not have to rotate wijfch the aid of a toothed belt or with the aid of spur gears as described above, and of course other means can be used, e.g..a V-belt, in which case the circumferential surface of the housing is provided with the appropriate groove. In addition, the gear housing can be rotated with the aid of a toothed ring mounted at the end wall of the housing, the ring having skew-cut teeth and with the driving power transmitted by bevel-gears. What is important in this connection is that the gear housing is rotated with the aid of rotational force

transmitting means arranged on the housing.

A still further modification resides in the way in which the motor is mounted on the gear. In the illustrated embodiment the motor is carried by a strut, although of course it can be suspended by its own shaft. A torque strut is arranged in this case to prevent the motor housing from rotating, the strut extending between the housing and the roll frame. This strut can be such as a lever which is mounted for longitudinal displacement in the roll frame. Such a mounting permits the monitored roll to be displaced axially in the roll frame (for side indexing).

The invention can be modified in many ways and varied within the scope of the accompanying claims.