Control device for blowing and suction air in printing presses
United States Patent 3916790
A device for use in a sheet-fed printing press for controlling the application of air at an air head cooperating with a cyclically moving element connected to the press drive. "On" and "off" valves are interposed in the air line operated by cams coupled to the press drive. The valves have "on" and "off" control elements operated by individual servo systems so arranged that the interval during which air is applied is shifted in phase automatically in accordance with press speed. In the preferred embodiment adjustment to the reference voltage and the link adjustment are provided in at least one of the servo systems for changing the servo gain and for changing the control point to permit changing the length of the interval during which air is applied as well as the phase of the interval, respectively. More specifically, "on" and "off" valves are connected in series in the line, the respective servos producing arcuate shifting movement about respective cams.
US Patent References:
Apparatus for controlling web tension
George et al. - May 1962 - 3032245
/3074712.html
Holt, Jr. et al. - January 1963 - 3074712
Sheet handling apparatus
Staines - July 1967 - 3330554
Web lapping apparatus
Nystrand et al. - August 1967 - 3338575
AIR AND VACUUM CONTROL MECHANISM FOR A DUPLICATING MACHINE
Gallagher - September 1969 - 3469526
Apparatus for controlling web tension
George et al. - May 1962 - 3032245
/3074712.html
Holt, Jr. et al. - January 1963 - 3074712
Sheet handling apparatus
Staines - July 1967 - 3330554
Web lapping apparatus
Nystrand et al. - August 1967 - 3338575
AIR AND VACUUM CONTROL MECHANISM FOR A DUPLICATING MACHINE
Gallagher - September 1969 - 3469526
Application Number:
05/516668
Publication Date:
11/04/1975
Filing Date:
10/21/1974
View Patent Images:
Export Citation:
Assignee:
Roland Offsetmaschinenfabrik Faber & Schleicher AG
Primary Class:
Other Classes:
271/108, 271/96, 493/418
International Classes:
B65H3/08; B65H3/48; B41F13/24
Field of Search:
271/90-108,3R,3A,5 101/232,233-243 270/69,1,7,8,9-15,17,18,19,38,42,43,44,45,47,52,54,58,60,70,71 226/10,20,39,130,131,157,158,165,188 95/53D,53AC
US Patent References:
| 3512479 | AUTOMATED OVERCHUTE FEED MECHANISM FOR A PRINTING PRESS AND CONTROL SYSTEMS THEREFOR | May 1970 | McHenry et al. | |
| 3635159 | OVERCHUTE FEED APPARATUS FOR ROTARY PRINTING MACHINE | January 1972 | Keeler et al. | |
| 3785640 | APPARATUS FOR SEPARATING AND FEEDING DOCUMENTS | January 1974 | Delcano et al. | |
| 3831930 | PAPER FEEDING APPARATUS FOR USE IN PRINTING MACHINE | August 1974 | Shimizu |
Primary Examiner:
Michell, Robert W.
Assistant Examiner:
Millin V.
Attorney, Agent or Firm:
Wolfe, Hubbard, Leydig, Voit & Osann Ltd.
Claims:
What is claimed is
1. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element, valve means interposed in the line, a first valve operator coupled to the press drive and having a phase adjusting element for turning on the valve means at a first phase position of the cyclically moving element, a second valve operator coupled to the press drive and having a phase adjusting element for turning off the valve means at a second phase position of the cyclically moving element, means providing an output signal in accordance with press speed, and means responsive to the output signal for acting upon the phase adjusting elements for shifting the phase of application of air at the head automatically in accordance with changes in press speed.
2. The combination as claimed in claim 1 in which the means responsive to the output signal is in the form of separate servo systems separately acting upon the phase adjusting elements.
3. The combination as claimed in claim 2 in which at least one of the servo systems includes means for controlling the servo gain thereby to change the magnitude of phase differential between the "on" and "off" points in accordance with changes in press speed.
4. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, an "on" air valve and a "off" air valve connected in series with the line, cams coupled to the press drive for operating the air valves, shiftable "on" and "off" control elements associated with the respective valves for shifting the phase of the "on" and "off" positions with respect to the press drive, means providing an output signal in accordance with press speed, a first servo system responsive to the output signal for shifting the "on" control element, and a second servo system responsive to the output signal for shifting the "off" control element in the same direction thereby to shift in phase the interval during which air is applied to the head automatically in accordance with changes in press speed.
5. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, valve means interposed in the air line including first and second valve elements, cams driven by the press drive for operating the valve elements so that air is turned on and turned off at predetermined points of phase with respect to the press drive, the valve elements having respective control elements which are relatively shiftable about the respective cams, and separate servo systems having their outputs coupled to the respective control elements for shifting the control elements simultaneously in accordance with changes in press speed.
6. The combination as claimed in claim 5 in which means are provided in at least one of the servo systems for changing the servo characteristics thereof thereby to vary the length of the angular interval of application of air as a function of press speed.
7. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, an "on" air valve and a "off" air valve connected in series with the line, overlapping cams coupled to the press drive for sequentially operating the air valves to produce an "on" condition in which the two valves are both open to flow of air, "on" and "off" control elements associated with the respective valves and separately shiftable for separate control of the "on" and "off" points of phase, and separate means for adjusting the control elements in accordance with changes in press speed for shifting in phase the interval during which air is applied to the head as well as varying the angular duration of the interval.
1. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element, valve means interposed in the line, a first valve operator coupled to the press drive and having a phase adjusting element for turning on the valve means at a first phase position of the cyclically moving element, a second valve operator coupled to the press drive and having a phase adjusting element for turning off the valve means at a second phase position of the cyclically moving element, means providing an output signal in accordance with press speed, and means responsive to the output signal for acting upon the phase adjusting elements for shifting the phase of application of air at the head automatically in accordance with changes in press speed.
2. The combination as claimed in claim 1 in which the means responsive to the output signal is in the form of separate servo systems separately acting upon the phase adjusting elements.
3. The combination as claimed in claim 2 in which at least one of the servo systems includes means for controlling the servo gain thereby to change the magnitude of phase differential between the "on" and "off" points in accordance with changes in press speed.
4. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, an "on" air valve and a "off" air valve connected in series with the line, cams coupled to the press drive for operating the air valves, shiftable "on" and "off" control elements associated with the respective valves for shifting the phase of the "on" and "off" positions with respect to the press drive, means providing an output signal in accordance with press speed, a first servo system responsive to the output signal for shifting the "on" control element, and a second servo system responsive to the output signal for shifting the "off" control element in the same direction thereby to shift in phase the interval during which air is applied to the head automatically in accordance with changes in press speed.
5. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, valve means interposed in the air line including first and second valve elements, cams driven by the press drive for operating the valve elements so that air is turned on and turned off at predetermined points of phase with respect to the press drive, the valve elements having respective control elements which are relatively shiftable about the respective cams, and separate servo systems having their outputs coupled to the respective control elements for shifting the control elements simultaneously in accordance with changes in press speed.
6. The combination as claimed in claim 5 in which means are provided in at least one of the servo systems for changing the servo characteristics thereof thereby to vary the length of the angular interval of application of air as a function of press speed.
7. In a device for controlling the application of air at an air head in a sheet-fed printing press, the combination comprising a press drive, a cyclically moving element in the press coupled to the press drive, an air supply including an air line, an air head connected to the air line and cooperating with the cyclically moving element in phased relation, an "on" air valve and a "off" air valve connected in series with the line, overlapping cams coupled to the press drive for sequentially operating the air valves to produce an "on" condition in which the two valves are both open to flow of air, "on" and "off" control elements associated with the respective valves and separately shiftable for separate control of the "on" and "off" points of phase, and separate means for adjusting the control elements in accordance with changes in press speed for shifting in phase the interval during which air is applied to the head as well as varying the angular duration of the interval.
Description:
In a sheet-fed printing press it is conventional to control the sheets, particularly during transfer, by air heads which apply pressure or suction synchronized with a cyclically moving element connected to the press drive. Means have been provided for manual adjustment of the phase and duration of the applied air. However, in spite of careful phase adjustment, the results are often disappointing and a sheet often gets out of control requiring shut-down of the press and associated conveyor system and setting up the possibility of a jamming situation which might result in damage to the press or hazard to the operator.
It is, accordingly, an object of the present invention to provide an improvement in devices for controlling application of air which has been found to produce more reliable and consistent results, particularly when changing the speed of the press drive as is required under practical press room conditions.
It is more specifically an object to provide a device, or system, for controlling application of air in the form of either pressure or suction in which the phase of the point of turn-on and the phase of the point of turn-off are promptly and automatically shifted in a coordinated manner automatically in accordance with changes in press speed. It is a related object to provide an air supply system in which the length of the air supply interval may be changed automatically in accordance with press speed in addition to gross shifting of the interval with respect to the phase of the press drive. It is yet another object of the present invention to provide an air supply system which is automatic and consistent in operation, which is highly reliable, and which may be constructed at low cost for application to new presses or presses of existing design already in the field and which is substantially free of maintenance problems.
Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:
FIG. 1 is a diagram illustrating a system constructed in accordance with the present invention.
FIG. 2 is a typical phase shift diagram showing characteristics obtainable with the system of FIG. 1.
In the following description it will be assumed that suction is to be applied by the air head, and the description of operation will be set forth in terms of suction, but it will be one understood by one skilled in the art that the invention is not limited thereto and that the system is equally applicable to an air head intended for the blowing of a stream of pressurized air on an accurately phased, cyclical basis. The term "air supply" is accordingly used herein in a generic sense.
Turning to FIG. 1, a press drive indicated at 10 has a mechanical connection 11 to a cyclically moving press element indicated generally at 12. Such cyclically moving element may, in a practical case, be any element which transfers or transports individual sheets on a timed basis, or the element 12 may, if desired, be considered as a cyclically moving sheet. Positioned adjacent the path of movement of the sheets is an air head 13 connected to a line 14, the other end of which is connected to a source of suction 15 although, as stated, a source of pressure 16 may be substituted therefor.
For controlling flow of air through the line 14 an "on" valve 20 is provided having a spool or plunger 21, at the lower end of which is a cam follower 22. Cooperating with the cam follower is a cam 23 mounted upon a shaft 24.
Similarly, for turning off the air flow, a second or "off" valve 30 is provided having a plunger 31 and cam follower 32 cooperating with a cam 33 mounted upon a shaft 34. Where the shafts 24, 34 are separate, they may be coupled together by a timing belt 35 or equivalent, but in a practical case the shafts 24, 34 will be integral with one another, with a mechanical connection 36 to the press drive 10. For convenience in making changes in initial phasing, the cams 23, 33 may have an adjustable "set screw" type of connection with their shafts or driving elements, but the cams should be kept in overlapping relation.
With the valves 20, 30 oriented as shown, and with the cams rotating in the direction indicated by the arrows, it will be apparent that both of the valves will be shut off during most of the rotative cycle. In a typical on-off cycle, the leading edge of cam 33 will turn on valve 30. This will not initiate flow of air; however, when the leading edge of cam 23 turns on valve 20 a continuous air passage is established. Air flow continues until the cam follower of valve 30 drops off of the end of cam 33 to terminate a single air cycle.
In accordance with the present invention the cam followers associated with the valves have associated control elements for relatively shifting the cam followers with respect to the associated cams. Further in accordance with the invention means are provided for generating a signal which varies in accordance with press speed, and respective servo systems, responsive to such speed signal, are provided for shifting the respective control elements to bring about a shifting in the phase of the "on" and "off" points of the air valves thereby to shift the air application interval constantly and automatically, preferably on a linear basis, with respect to press speed.
Taking up first the servo system which controls the "on" valve 20, the control element is in the form of a plate 40 which holds the valve and which is arcuately shiftable about the center of the cam 23. To permit free shifting movement the plate 40 has arcuate slots 41 slideably engaged by respective studs 42 anchored in the press frame. For moving the control element 40 a motor 43 is provided having a worm gear set 44 which positions an output arm 45 which is connected by a link 46 to the control element 40. For positioning the arm 45 with servo action in accordance with press speed, a servo system 50 is provided which includes a tachometer generator 51 which has a driving connection 52 to the press drive and which is capable of producing a direct output voltage in accordance with press speed. Positional follow-up is provided by a potentiometer 53 having a slider 54 which is connected to the arm 45 by a mechanical connection, or link, indicated at 55. Bridging the potentiometer is a variable source of reference voltage 56 which is normally maintained constant but which is nonetheless adjustable as will be later discussed.
The tachometer generator 51 and the potentiometer "output" circuits are connected in a loop with opposing polarity. For the purpose of increasing power capability, the servo loop circuit is fed into an amplifier 57 having linear output characteristics and of a type, employing solid state, available in the market.
In operation an increase in speed brought about by the speed control associated with the press drive causes an increase in the output voltage of the tachometer generator. Such output signal is applied to the input of the amplifier 57 energizing the motor 43 to swing the arm 45 to the left causing the valve 20 to rock counterclockwise to turn on the valve at an earlier point of phase. Movement of the control element 40 is accompanied by follow-up movement of the potentiometer slider to cancel out the increase in tachometer voltage so that the motor 43 comes to rest with the valve 20 in its new position.
Conversely, any decrease in press speed from the reference level causes a drop in the tachometer signal applying a voltage of opposite polarity to the amplifier 57 rotating the motor 43 in the opposite direction to rock the valve 20 in the clockwise direction to retard the turning on of the valve and accompanied by follow-up action at the potentiometer.
A similar control element, motor, and servo system are employed for adjusting the "off" valve 30 with corresponding parts being indicated by similar reference numerals with addition of subscript a. Since the two servo systems 50, 50a share the same tachometer generator 51, isolating diodes 58, 58a are connected to the output terminal of the generator although, if desired, separate, matched tachometer generators may be employed without departing from the invention.
The coordination between the two servo systems is apparent upon inspection of FIG. 2 where the variation in phase as a function of press speed for the valve 20 is indicated at 61 and for the valve 30 at 62. The stop motion positions in FIG. 1 indicated at R will be assumed to be the zero reference angle indicated at the ordinate of FIG. 2. Point 63 indicates the angle of the "on" point of cam 23, which angle is approximately -20° (positive values being indicated in the counterclockwise direction). Similarly, the point of turn-off indicated at 64 in FIG. 2 bears an angle of approximately 60° with respect to the reference R.
With the two servo systems adjusted for symmetry, the characteristics 61, 62 will be parallel to one another so that the effect of a change in press speed will be to advance and retard the "air on" and "air off" times in the same direction and to equal degree. In the illustrated embodiment an increase in press speed serves to advance, in phase, the interval during which air is applied without changing the angular length of the interval.
However, the invention is not limited thereto and it is one of the features of the invention that the servo gain and control point of one of the servo systems may be varied with respect to the other to cause the phase characteristics to be non-parallel, for example, divergent. This may be of distinct advantage where it is desired to increase the angular length of the air interval to secure a greater relative time during which the air acts, as the press speed is progressively increased. Thus the position and slope of the characteristic curve 61 may be varied, with respect to the curve 62, by relative adjustment of the reference voltage 56 and by providing means, in the connection 55, for changing the effective length of such connection. Such adjusting means has been referred to in FIG. 1 as the "link adjustment" 59.
It will be apparent to one skilled in the art that elements 56, 59 may both be adjusted to shift the phase response curve from position 61, in FIG. 2, to the "divergent" (dot-dash) position 65. Alternatively, if desired, the "on" and "off" curves 61, 62 may be made convergent by adjusting elements 56, 59 in the opposite sense, in either event producing an automatic change in phase differential as a function of speed. Moreover, if it is desired primarily to change, for example increase, the angular length of the "air on" time without changing its phase, this, too is possible in the present system by adjusting the sense and gain of the servo system 50a so that its response curve 62 slopes upwardly while the response curve 65 slopes downwardly, as shown.
It will be understood by one skilled in the art that the servo systems 50, 50a are shown by way of example only. While an electrical system employing a tachometer generator is preferred, it will be apparent that a purely mechanical servo system may be employed without departing from the invention and that the term "output signal" used in connection with the tachometer generator is not necessarily limited to a signal of an electrical nature.
It will be apparent that the present air control system enables the timing of the air interval to be optimum, not only for a particular reference press speed but over a wide range of speed as encountered in a practical press room. Moreover, by changing the servo gain and control point of the respective systems, the "on" and "off" points of phase may be independently controlled as a function of speed providing a wide adjustment capability and a degree of flexibility which enables the control system to be employed in any press and for any air controlling purpose. In the illustrated embodiment the air interval is limited, because of the length of the cam surfaces 23, 33, to a maximum of about 120°. It will be apparent, however, that the cam surfaces may be lengthened or shortened as a matter of designer's choice as long as an integral relationship is maintained between the cam drive and the cyclically moving element 12 which cooperates with the air head.
It is, accordingly, an object of the present invention to provide an improvement in devices for controlling application of air which has been found to produce more reliable and consistent results, particularly when changing the speed of the press drive as is required under practical press room conditions.
It is more specifically an object to provide a device, or system, for controlling application of air in the form of either pressure or suction in which the phase of the point of turn-on and the phase of the point of turn-off are promptly and automatically shifted in a coordinated manner automatically in accordance with changes in press speed. It is a related object to provide an air supply system in which the length of the air supply interval may be changed automatically in accordance with press speed in addition to gross shifting of the interval with respect to the phase of the press drive. It is yet another object of the present invention to provide an air supply system which is automatic and consistent in operation, which is highly reliable, and which may be constructed at low cost for application to new presses or presses of existing design already in the field and which is substantially free of maintenance problems.
Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:
FIG. 1 is a diagram illustrating a system constructed in accordance with the present invention.
FIG. 2 is a typical phase shift diagram showing characteristics obtainable with the system of FIG. 1.
In the following description it will be assumed that suction is to be applied by the air head, and the description of operation will be set forth in terms of suction, but it will be one understood by one skilled in the art that the invention is not limited thereto and that the system is equally applicable to an air head intended for the blowing of a stream of pressurized air on an accurately phased, cyclical basis. The term "air supply" is accordingly used herein in a generic sense.
Turning to FIG. 1, a press drive indicated at 10 has a mechanical connection 11 to a cyclically moving press element indicated generally at 12. Such cyclically moving element may, in a practical case, be any element which transfers or transports individual sheets on a timed basis, or the element 12 may, if desired, be considered as a cyclically moving sheet. Positioned adjacent the path of movement of the sheets is an air head 13 connected to a line 14, the other end of which is connected to a source of suction 15 although, as stated, a source of pressure 16 may be substituted therefor.
For controlling flow of air through the line 14 an "on" valve 20 is provided having a spool or plunger 21, at the lower end of which is a cam follower 22. Cooperating with the cam follower is a cam 23 mounted upon a shaft 24.
Similarly, for turning off the air flow, a second or "off" valve 30 is provided having a plunger 31 and cam follower 32 cooperating with a cam 33 mounted upon a shaft 34. Where the shafts 24, 34 are separate, they may be coupled together by a timing belt 35 or equivalent, but in a practical case the shafts 24, 34 will be integral with one another, with a mechanical connection 36 to the press drive 10. For convenience in making changes in initial phasing, the cams 23, 33 may have an adjustable "set screw" type of connection with their shafts or driving elements, but the cams should be kept in overlapping relation.
With the valves 20, 30 oriented as shown, and with the cams rotating in the direction indicated by the arrows, it will be apparent that both of the valves will be shut off during most of the rotative cycle. In a typical on-off cycle, the leading edge of cam 33 will turn on valve 30. This will not initiate flow of air; however, when the leading edge of cam 23 turns on valve 20 a continuous air passage is established. Air flow continues until the cam follower of valve 30 drops off of the end of cam 33 to terminate a single air cycle.
In accordance with the present invention the cam followers associated with the valves have associated control elements for relatively shifting the cam followers with respect to the associated cams. Further in accordance with the invention means are provided for generating a signal which varies in accordance with press speed, and respective servo systems, responsive to such speed signal, are provided for shifting the respective control elements to bring about a shifting in the phase of the "on" and "off" points of the air valves thereby to shift the air application interval constantly and automatically, preferably on a linear basis, with respect to press speed.
Taking up first the servo system which controls the "on" valve 20, the control element is in the form of a plate 40 which holds the valve and which is arcuately shiftable about the center of the cam 23. To permit free shifting movement the plate 40 has arcuate slots 41 slideably engaged by respective studs 42 anchored in the press frame. For moving the control element 40 a motor 43 is provided having a worm gear set 44 which positions an output arm 45 which is connected by a link 46 to the control element 40. For positioning the arm 45 with servo action in accordance with press speed, a servo system 50 is provided which includes a tachometer generator 51 which has a driving connection 52 to the press drive and which is capable of producing a direct output voltage in accordance with press speed. Positional follow-up is provided by a potentiometer 53 having a slider 54 which is connected to the arm 45 by a mechanical connection, or link, indicated at 55. Bridging the potentiometer is a variable source of reference voltage 56 which is normally maintained constant but which is nonetheless adjustable as will be later discussed.
The tachometer generator 51 and the potentiometer "output" circuits are connected in a loop with opposing polarity. For the purpose of increasing power capability, the servo loop circuit is fed into an amplifier 57 having linear output characteristics and of a type, employing solid state, available in the market.
In operation an increase in speed brought about by the speed control associated with the press drive causes an increase in the output voltage of the tachometer generator. Such output signal is applied to the input of the amplifier 57 energizing the motor 43 to swing the arm 45 to the left causing the valve 20 to rock counterclockwise to turn on the valve at an earlier point of phase. Movement of the control element 40 is accompanied by follow-up movement of the potentiometer slider to cancel out the increase in tachometer voltage so that the motor 43 comes to rest with the valve 20 in its new position.
Conversely, any decrease in press speed from the reference level causes a drop in the tachometer signal applying a voltage of opposite polarity to the amplifier 57 rotating the motor 43 in the opposite direction to rock the valve 20 in the clockwise direction to retard the turning on of the valve and accompanied by follow-up action at the potentiometer.
A similar control element, motor, and servo system are employed for adjusting the "off" valve 30 with corresponding parts being indicated by similar reference numerals with addition of subscript a. Since the two servo systems 50, 50a share the same tachometer generator 51, isolating diodes 58, 58a are connected to the output terminal of the generator although, if desired, separate, matched tachometer generators may be employed without departing from the invention.
The coordination between the two servo systems is apparent upon inspection of FIG. 2 where the variation in phase as a function of press speed for the valve 20 is indicated at 61 and for the valve 30 at 62. The stop motion positions in FIG. 1 indicated at R will be assumed to be the zero reference angle indicated at the ordinate of FIG. 2. Point 63 indicates the angle of the "on" point of cam 23, which angle is approximately -20° (positive values being indicated in the counterclockwise direction). Similarly, the point of turn-off indicated at 64 in FIG. 2 bears an angle of approximately 60° with respect to the reference R.
With the two servo systems adjusted for symmetry, the characteristics 61, 62 will be parallel to one another so that the effect of a change in press speed will be to advance and retard the "air on" and "air off" times in the same direction and to equal degree. In the illustrated embodiment an increase in press speed serves to advance, in phase, the interval during which air is applied without changing the angular length of the interval.
However, the invention is not limited thereto and it is one of the features of the invention that the servo gain and control point of one of the servo systems may be varied with respect to the other to cause the phase characteristics to be non-parallel, for example, divergent. This may be of distinct advantage where it is desired to increase the angular length of the air interval to secure a greater relative time during which the air acts, as the press speed is progressively increased. Thus the position and slope of the characteristic curve 61 may be varied, with respect to the curve 62, by relative adjustment of the reference voltage 56 and by providing means, in the connection 55, for changing the effective length of such connection. Such adjusting means has been referred to in FIG. 1 as the "link adjustment" 59.
It will be apparent to one skilled in the art that elements 56, 59 may both be adjusted to shift the phase response curve from position 61, in FIG. 2, to the "divergent" (dot-dash) position 65. Alternatively, if desired, the "on" and "off" curves 61, 62 may be made convergent by adjusting elements 56, 59 in the opposite sense, in either event producing an automatic change in phase differential as a function of speed. Moreover, if it is desired primarily to change, for example increase, the angular length of the "air on" time without changing its phase, this, too is possible in the present system by adjusting the sense and gain of the servo system 50a so that its response curve 62 slopes upwardly while the response curve 65 slopes downwardly, as shown.
It will be understood by one skilled in the art that the servo systems 50, 50a are shown by way of example only. While an electrical system employing a tachometer generator is preferred, it will be apparent that a purely mechanical servo system may be employed without departing from the invention and that the term "output signal" used in connection with the tachometer generator is not necessarily limited to a signal of an electrical nature.
It will be apparent that the present air control system enables the timing of the air interval to be optimum, not only for a particular reference press speed but over a wide range of speed as encountered in a practical press room. Moreover, by changing the servo gain and control point of the respective systems, the "on" and "off" points of phase may be independently controlled as a function of speed providing a wide adjustment capability and a degree of flexibility which enables the control system to be employed in any press and for any air controlling purpose. In the illustrated embodiment the air interval is limited, because of the length of the cam surfaces 23, 33, to a maximum of about 120°. It will be apparent, however, that the cam surfaces may be lengthened or shortened as a matter of designer's choice as long as an integral relationship is maintained between the cam drive and the cyclically moving element 12 which cooperates with the air head.