GB2190043A

GB2190043A - Printing press component controlling device

Info

Publication number: GB2190043A
Application number: GB08709622A
Authority: GB
Inventors: Anton Rodi
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1986-04-24
Filing date: 1987-04-23
Publication date: 1987-11-11
Anticipated expiration: 2007-04-23
Also published as: FR2597791B1; FR2597791A1; DE3613968A1; GB8709622D0; JPS62257848A; GB2190043B

Abstract

This invention provides a device for exerting a force on a component of a printing press, comprising a force-exerting element and actuating means for said element, the arrangement being such that the force exerted by the said element is controllable by means of a control apparatus at a desired but adjustable value. More specifically, in one form of device in accordance with the invention the force-exerting element comprises a stalled electric motor wherein those components which move in relation to one another are, for a given input to the motor, and at least within a predetermined range of relative movement of the said components, subjected to a constant force produced by the motor or to a constant torque produced by the motor. Fluid pressure force generation is also disclosed. The control circuits for either electromagnetic or fluid pressure devices may include feedback. <IMAGE>

Description

SPECIFICATION Printing press component controlling device This invention relates to a device for exerting a force on a component of a printing press.

In many cases, components of printing presses require forces to be exerted on them which are to be kept constant, irrespective of variable or unknown quantities thatwouldtend to alterthoseforces.

Examples of this requirement that can be mentioned are devices for bringing rollers into engagement and for pressing them against each other, in which the force acting on the rollers is to be independent of the instantaneous positions ofthe rollers.

Sheet-conveying or sheet-guiding apparatuses, too, require forces which are, as far as possible, to remain constant. Furthermore, in sheet-guiding apparatuses, for example, it should be possible for the forces to be suitably selectable as a function of the sheet thickness, the number of sheets on top of each other (more particularly in a continuous-stream feeder), and the quality of the surface ofthe sheet.

Adjustable forces on components of printing presses are exerted in various ways. Thus, the force can be exerted by a spring. The force ofthe spring is proportional to the travel of the spring, however, and is therefore not constant if the part exposed to the force is moved. In addition, the spring represents an energy-storage device, and there is therefore a tendency towards resonance vibrations. Another possibility consists in utilising the weight of a body as the force in question. In this case, the mass inertia also increases with the force exerted, and the force is difficult to change.

It is an object of the present invention to provide a device of the initially mentioned kind in which the force is easily adjustable, and with which there is the possibility of obviating the aforementioned disadvantages.

According to the invention there is provided a deviceforexerting a force on a component of a printing press, comprising a force-exerting element and actuating means for said element, the arrangement being such that the force exerted by the said element is controllable by means of a control apparatus at a desired but adjustable value.

Desirably the force exerted is for the most part independentofthe position and of the movement of the component on which theforce is exerted.

An advantage of the invention is that the force can easily be varied by means ofthe control apparatus.

The force exerted may be either substantially independent of the position and movement of the component exposed to it, without this requiring any action on the part of the control apparatus; orthe aforementioned force may be kept substantially independent of the aforementioned parameters by virtue of the position of the component exposed to the force being utilised to control the force-exerting element.

The force-exerting element may operate with a fluid medium. Thus, a pneumaticforce-exerting element may be provided. Although, in this case, the fluid medium, compressed air for example, may mean thatthe force-exerting elementtendsto execute vibrations because the fluid medium is compressible, this vibrative tendency can be kept low by means of a feedback-control device which rapidly regulates the pressure of the fluid medium, and which, in doing so, advantageously also takes account of the instantaneous position of the piston exposed to the fluid medium.

If the device according to the invention operates with a liquidfluid medium, then the tendency to execute vibrations is low owing to the virtual absence of compressibility ofthe fluid. However, to enabletheforce-exerting element to follow quickly movements of the printing press component exposed to it, without there bei ng a noticeable change in the force exerted, it is advantageous to provide a feedback-control device which will act quickly to keep the pressure oftheflow medium constant.

The force-exerting elementofthe device of the invention may comprise an electric motorwherein those components which move in relation to one another(e.g. statorand rotor) are,fora given inputto the motor, and at least within a predetermined range of relative movement of the said components, subjected to a constant force produced by the motor orto a constant torque produced by the motor.

In the force-exerting element is a motor suitable for a continuously rotating drive, the motor, when used astheforce-producing element, does not in general rotate continuously, but is braked to a stop by the component on which it exerts its force. It is possible without difficulty to find (or, if necessary, to design specially) a motor which, for a g iven input, produces a sufficiently constant force within the margin of movement possible for the respective application.If a standard type of electric motor can be used, then the advantage lies in the great simplicity of the device. Afurther advantage is that the force produced by the motor or the torque produced by the motor is, at least within a specified range of movement, independent of the respective positions ofthe components ofthe motor that move in relation to one another. Finally, an advantage lies in the fact that the force exerted can be set and kept constant by electrical means, particularly by means of the motor current, more particularly the armature current. The setting and regulation of the motor current can be achieved cheaply, quickly and accurately with known simple means.

Since, despite the supply of armature current, the motor used to exert the force is stationary, the motor must be suitably rated and/or be separately cooled in orderto prevent damage due to overheating.

In the device of the invention, the force-exerting element may be a rotary motor. This can be realized in a particularly simple manner, and, in this case,in numerous applications, it will be possible to use a commercially available electric motor to produce the force or the torque, particularly a direct-current shunt-wound motor or a motorofsimilarelectrical behaviour.

In the device ofthe invention,the possible angle of rotation of the motor (as in a moving-coil pointer instrument) may be limited to an angle of less than 360 degrees. This may be appropriate in individual applications and has the advantage that, although use may be made of a direct-current motor, it does not in all cases require slip rings. In moving-coil pointer instruments, there is a uniform magnetic field only within a range of rotation of, for example, 90 degrees or 120 degrees ofthe moving coil. In contrast to moving-coil instruments, this form of device according to the invention does not necessarily require a return spring.

In the last-described case as well as in further forms of device according to the invention, it is possible, if or when the force exerted is to havethe value zero orthe component on which the force is exerted isevento be lifted off its base,forthisto be achieved by reversing the direction of the armature current.

A device according to the invention may employ an arm which at one end is mounted on the shaft of the motor and which at the other end is in contact with the component on which the force is to be exerted. Inthiscase, by appropriate selection ofthe length ofthe arm and of the angle enclosed by the longitudinal direction ofthe arm relative to the direction of the force exerted, it is possible forthe force to be made largely independent of changes in position ofthe component exposed to the force.

The motor may, as already mentioned, preferably be a direct-current motor.

A device according to the invention may employ a feedback-control device whereby the armature current of the motor is kept constant at a selected value. Thus one can ensure the particularly accurate maintenance of a constantforce.

It is also possible, in a device according to the invention,to have the motor in the form of a linear motor. In this case, the motor may, in particular, be in the form of a polyphase motor, in particular a three-phase motor. Various other kinds of motor (e.g. hydraulic, pneumatic) may, in principle, also be used.

So far, it has been contemplated that the force exerted by the present device isto be independentof the movement ofthe component exposed to the force. It is also possible, however, as provided for in accordance with a modified form of the i nvention, to provide a control apparatus, said control apparatus varying in a predetermined mannertheforce orthe torque of the motor as a function of the movement of the component exposed to the force orto the torque.

This makes it possible, in particular, to achieve any predeterminable characteristic ofthe force, or ofthe torque, as a function of the movement.

Furtherfeatures and advantages of the invention will become apparent from the following description with reference to the accompanying diagrammatic drawings, in which: Figure lisa schematic representation of a device forexerting aforceactingona pressure roller in a printing press; and Figure2 is a block diagram of a control device.

In Figure 1, an arm 2 carries at one of its ends a pressure roller 4; the other end of the arm 2 is attached to the shaft 6 of a motor 8, this being a d.c.

shunt-wound motor. The longitudinal direction of the arm 2 deviates by a small angle from the horizontal plane. Disposed between the pressure roller 4 and a flat base 10 is an object which is to be pressed into contact by the pressure roller 4, this being in the present example a sheet 12 of paper (shown only in part, its thickness being greatly exaggerated in the drawing). An excitation winding ofthe motor 8 is supplied via electric leads 14with the excitation current from an excitation unit 16, said excitation unit 16 providing a constant current. Via leads 22, a control apparatus 20 supplies the armature currentforthe motor 8. It is possible also to use a motor whose field is provided buy a permanent magnet. Other motors may additionally be used.

The direction of the current is such thatthetorque exerted by the motor 8 on the arm 2 acts in an anticlockwise direction. A rotary motion is prevented by the fact that the pressure roller4 is supported on the base 10, through the intermediary ofthe sheet 12.

In this connection, the pressure roller 4 exerts a force F on the sheet 12. If the weight of the pressure roller4 and the arm 2 is neglected, the force F can be calculated as F = M/(1 cos p), where M is the torque ofthe motor 8 and 1 is the length of the arm 2.

Provided that, in the event of a change in the thickness of the sheet 12, there is sufficiently little change in the value cos , theforce F will be sufficiently independent of the position of the pressure roller 4. It is assumed in this connection that, for all relevant positions of the arm 2, the motor 8 produces the same torque, given that the electrical input is kept constant.

If the change in the rotary position of the arm 2 becomes so great that the change in the value cos p is not negligible, there is the possibility of measuring the rotary position of the arm 2 by means of a suitable sensor, for example by means of a potentiometer, and of controlling the armature current as a function of the rotary position of the arm 2, in such a mannerthat, irrespective ofthecurrent position of the arm 2, theforne F has (with sufficient accuracy) the desired value. The arrangement may be such that the influence of the weight of the arm 2 on the force F, which varies as a function ofthe respective position of the arm, is also taken into account.

If the arrangement can be made such that the arm 2 extends horizontally and such that the pivoting motions of the arm 2 are negligible, then cos will have the value 1, and control of the armature current is not necessary.

In the control apparatus 20 shown in Figure 2,the setpoint of the armature current ofthe motor 8, and thus the torque, can be selected either by means of a computer 41 or by means of a manually adjustable setpoint device 42. The outputs ofthetwo last-mentioned devices are connected to the inputs of a selector switch 44, by means of which it is possible to select either of the aforementioned devices.

From the selector switch 44, the signal supplied from one ofthe devices 41 or 42, present in the form of a d.c. signal, reaches the two-pole setpoint input of a current control loop 47, the output ofwhich supplies the armature currentforthe motor 8. A resistor48,through which the armature current flows, supplies a voltage which is proportional to the armature current, and which is fed to the (likewise two-pole) actual-valve input of the current control loop 47. The current control loop 47 regulates the armature current so that there is a zero difference between its two input voltages.

Sensors 50,51 may be connected to the computer 41, with the computer 41 generating setpointsforthe armature current that are dependent on the output signals from the sensors, preferably from a table contained in a memoryforthe armature current as a function of the respective sensor signal. One ofthe sensors may be the aforementioned potentiometer which measures the current position of the arm 2.

If the computer 41 is to deliver different output signals as a function ofthe signals supplied bythe sensors 50 and 51 inordertoensurethatthe armature current produced is dependent on the aforementioned signals, then the outputsignals of the computer may be formed as a function of tables that are contained in a memory in the computer. This makes it possible quickly and by simple means to store in the memory any desired characteristic ofthe dependence of the armature current on the aforementioned signals.Instead ofthis, it would also be possible to produce the desired characteristic by means of a network, set up using diodes, which, withoutthe participation of a controllable computing device,would supply an analogueoutputsignalasa function of an analogue input signal supplied to it.

With such a diode network, as in a case in which the aforementioned characteristic is formed by means of a computer, this characteristic will often be found, on close scrutiny, to be a joining-together of individual straight orvirtually straight lines.

If the armature current is varied as a function of the thickness of the sheet passing underthe pressure roller 4, which was mentioned above as a possibility, it may in certain cases be desired not to vary the armature current if there are only brieffluctuations in thickness of the kind that may arise, for example, from the roughness of the paper. In such a case, it is merely necessary so to select the control time constant ofthe control device 20 that such brief fluctuations in the thickness ofthe paper do not initiate feedback control, with the control device 20 therefore keeping the armature current constant.

Precisely in those cases in which, for example, the fluctuations in thickness occur in fractions of a millisecond, and the control device is unableto react to these brief fluctuations in thickness, owing to the time constant of the control being different from zero, it is of advantage for the force to remain constant. This largely prevents vibrations.

Frequently, a device for producing an adjustable force will not comprise all the components represented in Figure 2. Thus, frequently, the switch 44 will not be present, and the device will contain either the setpoint device 42 or, instead, the computer 41 with one sensor or two sensors 50,51.

In the arrangement shown in Figure 1, given that the armature current of the motor 8 is kept constant, there will be a noticeable change in the force F if the angle p deviates greatlyfrom 0 degrees,this corresponding to a substantial movement in height of the pressure roller 4. If, despite such a substantial movement in height of the pressure roller 4, the force F is to remain constant, given that the motorcurrent is kept constant, this can be achieved, in another form of device according to the invention, by having the pressure roller4 mounted on a lineariy displaceable straight rack, the teeth of said rack being engaged by a gearwheel, and said gearwheel being coupled directly or e.g. via intermediate gearwheels to the shaft of the motor 8. In this connection, it may be appropriateforthe direction of displacement of the aforementioned rack to be vertical. It may be sufficientforthe rack to press on the pressure roller.

In the construction described, an electric motor has been provided as the force-exerting element.

However, the principles described, particularly insofar as the control apparatus is concerned, may readily also be applied to a hydraulic or a pneumatic motor (rotating or linear), it being possible in this connection forthe control apparatus to be suitably modified without difficulty by those skilled in the art.

Generally, it will be understood that the invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

Claims

1. Device for exerting a force on a component of a printing press, comprising a force-exerting element and actuating means for said element, the arrangement being such that the force exerted by the said element is controllable by means of a control apparatusata desired butadjustablevalue.

2. Device according to claim 1, wherein a force-exerting element operating with a fluid medium is employed.

3. Device according to claim 2, wherein a pneumatic force-exerting element is employed.

4. Device according to claim 2, wherein an hydraulic force-exerting element is employed.

5. Device according to claim 1, wherein the force-exerting element comprises an electric motor wherein those components which move in relation to one another are, for a given input to the motor, and at least within a predetermined range of relative movementofthesaid components, subjected to a constantforce produced by the motororto a constanttorque produced by the motor.

6. Device according to any of the preceding claims, wherein the force-exerting element comprises a rotary motor.

7. Device according to claim 5 or 6, wherein the permitted angle of rotation ofthe motor is lessthan 360 degrees.

8. Device according to claim 6 or 7, wherein an arm is employed which at one end is mounted on the shaft of the motor and which atthe other end contacts the printing press component on which the force isto be exerted.

9. Device according to claim 6 or 7, wherein the shaft of the motor has coupled to it a gearwheel engaging the teeth of a linearly displaceable straight rack, said rack contacting or holding or otherwise being provided with a driving connection to the printing press component on which the force is to be exerted.

10. Device according to any of claims 5 to 9, wherein the motor is a direct-current motor.

11. Device according to claim 10, wherein a feedback-control device is provided whereby the armature current of the motor is kept constant art a selected value.

12. Device according to any of the preceding claims, wherein a feedback-control device is provided, the arrangement being such that the feedback-control device modifies the force orthe torque ofthe force-exerting element, as a function of asignal supplied to it, in accordancewitha predetermined characteristic.

13. Device according to any of claims 1 to 5, wherein the force-exerting element comprises a linear motor.

14. Device according to claim 1, substantially as described with reference to the accompanying drawing.