US3725756A

US3725756A - Hoist static control

Info

Publication number: US3725756A
Application number: US00068889A
Authority: US
Inventors: Connell H Mc; A Zeewy
Original assignee: Harris Intertype Corp
Current assignee: Harris Graphics Corp
Priority date: 1970-09-02
Filing date: 1970-09-02
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03

Abstract

A printing press includes an improved delivery pile hoist which supports a pile of sheets thereon and which lowers the pile of sheets so as to maintain the top of the pile between predetermined levels as sheets which travel through the press are added to the pile. The hoist includes a wound rotor motor for intermittently lowering the pile as the height of the pile increases as sheets are added thereto. The motor is operated intermittently by static circuitry which alternately renders the rotor windings conductive and non-conductive to currents induced therein. When the rotor windings are non-conductive, current will not flow through the rotor windings and the motor will not operate to move the hoist. When the windings are conductive, induced current will flow in the rotor windings and will cause the rotor to turn and lower the hoist. The present construction is operable to accurately control the height of the pile of sheets and has a simple and reliable construction which has a much longer life than conventional magnetic starters.

Description

United States Patent 1 McConnell et al.

[54] HOIST STATIC CONTROL [57] ABSTRACT [75] Inventors: Howard M. McConnell, Chagrin A printing press includes an improved delivery pile Falls; Abraham Zeewy, University hoist which supports a pile of sheets thereon and Heights, both of Ohio which lowers the pile of sheets so as to maintain the top of the pile between predetermined levels as sheets [73] Asslgnee Barns corporauon which travel through the press are added to the pile.

Cleveland, OhlO The hoist includes a wound rotor motor for intermit- [22] Filed: Sept. 2, 1970 tently lowering the pile as the height of the pile in- [211 App] 68 889 creases as sheets are added thereto. The motor is operated intermittently by static circuitry which alternately renders the rotor windings conductive and [52] U-S. Cl 318/482 non-conductive to currents induced therei r when the Int- Cl. rotor windings are norbconductive current not of Search 1 flow through the rotor windings and the motor not 271/62 operate to move the hoist. When the windings are conductive, induced current will flow in the rotor References Clted windings and will cause the rotor to turn and lower the hoist. The present construction is operable to accu- UNITED STATES PATENTS rately control the height of the pile of sheets and has a 3,529,224 9/1970 Bedford ..3l8/237 simple and reliable construction which has a much ,5 0 4/1970 u r et a ...3l8/237 longer life than conventional magnetic starters. 3,446,496 5/1969 Schwebel ..27l/62 Primary Examiner-Bernard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr. 5 Claims, 2 Drawing Figures AttorneyYount and Tarolli E J 2 r1 5'6 0 /84 -86 r88 44': I F 64 I l 424 I 1 gg 72%?? 2; 94 t e m FIR/N6 4/ 72 MODULE 70 PATENTEUAPRs 1073 lxx FIG1

F G /N VEN TORS l 2 Ham/A20 M m'colv/vaz ABRAHAM zs wy TTORNEYS HOIST STATIC CONTROL The present invention relates to a printing press having a delivery pile hoist which is controlled in an intermittent mode to adjust the pile height automatically and more specifically to a static control which intermittently renders the secondary windings of a wound rotor hoist motor alternately conductive and non-conductive.

The conventional way of controlling the operation of a motor is to connect a magnetic starter to the primary coils of the motor. While such a construction utilizing a magnetic starter is feasible, the life of a magnetic starter is limited and the magnetic starter must be periodically replaced. Replacement of the magnetic starter results in a shut-down of the machine with which the motor is associated. Moreover, since the magnetic starter controls the primary windings of the motor, the voltage and currents to be controlled by the magnetic starter are fixed by the requirements of the motor. This results in a disadvantage because freedom of choosing the voltages and currents to be controlled by the switching network is not readily obtained.

Accordingly, an object of the present invention is to provide a new and improved static switching system for controlling the intermittent operation of an apparatus driven incrementally by a wound rotor motor by rendering the secondary windings of the motor alternately conductive or non-conductive to respectively start and stop the motor and which overcomes the hereinabove disadvantages by providing a switching network wherein freedom of choosing voltages and currents to be controlled by the switching network is obtained and wherein the life of the switching system is increased over that of magnetic starters.

Another object of the present invention is to provide a new and improved pile hoist, such as a delivery hoist for a printing press, having a wound rotor motor for moving the hoist and a static switching system for controlling the pile hoist motor in an intermittent mode by rendering the secondary or rotor windings of the motor alternately conductive and non-conductive to induced current therein and which includes a plurality of controlled rectifiers which are rendered conductive in response to a variation in the pile height associated with the hoist to thereby enable the rotor windings to conduct induced current therein so that the rotor turns to move the hoist.

Still another object of the invention is to provide a new and improved pile hoist as noted in the next preceding paragraph wherein the hoist motor is a threephase wound rotor motor and a single resistor is utilized to load the plurality of rotor windings associated with the motor.

A further object of. the present invention is to provide a new and improved pile hoist having a threephase wound rotor motor for incrementally moving the hoist, a static switching system for controlling the motor in an intermittent mode by rendering the secondary of the motor alternately conductive and non-conductive to respectively start and stop the motor, means for continuously energizing the primary of the motor when the motor is operated in the intermittent mode and means for changing the phase relationship between the primary windings so as to reverse the direction in which the motor moves the hoist.

Further objects and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment of the present invention taken in conjunction with the following drawings wherein:

FIG. 1 is a schematic view of a delivery pile hoist associated with a printing press; and

FIG. 2 is a schematic representation of the control circuitry associated with the hoist motor.

The present invention generally relates to automatically controlling the pile height in a pile hoist associated with a printing press. As sheets are removed from or added to a pile, the height of the pile incrementally changes. When the height of the pile has changed by a predetermined amount, a pile hoist motor is actuated to bring the top of the pile back to a predetermined position. The pile hoist motor which is a wound rotor motor is utilized to adjust the position of the top of the pile automatically during feeding of sheets to the pile. The pile hoist motor is controlled by a switch which senses a predetermined incremental change in the height of the pile and operates to render the normally non-conductive secondary of the motor conductive to thereby enable induced current to flow in the rotor windings so as to allow the motor to lower the pile height.

Referring to the drawings, FIG. 1 illustrates a delivery pile hoist 10 which is associated with a printing press 12. The printing press 12 operates to print on a plurality of sheets in a well-known manner. After the sheets have been printed they are transferred to a transfer conveyor unit 14 disposed within the press. The transfer conveyor unit 14 delivers the sheets from the printing units to the suckers 18 which engage with the sheet and transfer the sheet to the pile 16 on the delivery pile hoist 10 in a well-known manner.

The delivery pile hoist 10 includes a platform 22 upon which the sheets 16 are supported. The platform 22 is supported by

cables

24 and 26 which are preferably attached to the four corners of the platform 22. For illustrative purposes, only two of the

cables

24 and 26 are illustrated but it should be understood that additional cables are located on the corners of the platform 22 which are not illustrated in FIG. 1.

The cable 24 extends upwardly from the corner of the platform 22 and is connected to a drum 28 which is supported for rotation with the shaft 30. The cable 26 extends vertically upward and around the drum 32 and is also associated with a drum 28 which is mounted on the shaft 30 for rotational movement therewith. It should be apparent that rotation of the shaft 30 in a clockwise direction will cause the

cables

24 and 26 to wrap around the drums 28 and the platform 22 will move upwardly. Rotation of the shaft 30 in a counterclockwise direction will effect counterclockwise rotation of the drums 28 and the

cables

24 and 26 will unwrap therefrom so as to lower the platform 22.

A worm wheel 34 is connected to the shaft 30 and rotation of the worm wheel 34 effects rotation of the shaft 30. The worm wheel 34 is meshed with a worm gear 36 which is disposed on the shaft 38 of a hoist motor 40. When the motor 40 is energized, the shaft 38 will be rotated and the worm gear 36 will rotate therewith. Rotation of the worm gear 36 will effect rotation of the worm wheel 34 in a counterclockwise direction to thereby rotate the shaft 30. Thus, it should be apparent that energization of the motor 40 will lower the platform 22.

The motor 40 is preferably a three-phase wound rotor induction motor. As is indicated diagrammatically in FIG. 2, three leads 42, 44, 46 supply power from a 3 phase power supply to energize the primary or operate to both raise and lower the hoist, i.e., the motor may rotate in either direction depending on the phase relationship of the windings. When the leads 42, 44 and 46 are normally energized the motor 40 will be operable to lower the hoist but when the phase relationship of the leads is reversed by

opening contacts

48, 50 and 52 and

closing contacts

41, 43 and 45 the motor will be operable to raise the hoist as is well known. As described hereinbelow'the

contacts

48, 50 and 52 will normally be closed and the

contacts

41, 43 and 45 will normally be opened during operation of the press 12.

The motor 40 includes an armature or rotor 54. The rotor 54 constitutes the secondary of the motor and has three phase Y-connected windings, not illustrated, which are connected by the brushes and slip rings 56, 58 and 60 in series with the

secondary conductors

78, 80 and 82 respectively in a well-known manner. The brushes and slip rings are shown schematically in FIG. 2 and are associated with circuitry 62 which is generally operable to render the secondary circuit of the motor conductive or non-conductive by opening and closing the circuits between the slip rings 56, 58 and 60. When the circuits between the slip rings are opened, the secondary circuit of the motor is non-conductive and, therefore, the rotor 54 doesnot turn in response to a field on the primary windings when the

contacts

48, 50 and 52 are closed. When the secondary circuit is closed the current flows through the circuitry 62 and the currentcauses rotation of the rotor 54 and a corresponding rotation of the worm gear 36 and the shaft 30.

The circuitry 62 includes a resistor 64, a plurality of diodes 66, 68 and 70 and a plurality of controlled rectifiers which are preferably the silicon controlled rectifiers or SCRs 72, 74 and 76. The slip rings 56, 58 and 60 are connected by the

leads

78, 80 and 82, respectively, to lines 84, 86, and88, respectively, of the circuitry 62. The lines 84, 86 and 88 are respectively disposed between the diode 66 and the SCR 72, the diode 68 and the SCR 74, and the diode 70 and the SCR 76. When the circuitry 62 is conducting secondary current which is induced in the secondary windings from the primary windings will flow between the slip rings and through the rotor windings so as to cause the rotor to turn. The current will flow through one of the loops in the circuitry 62 such as from the slip ring 56 through the lines 78, through the line 84, through the SCR 72, through the resistor 64 and then back through the

lead

80 or 82 to one of the other slip rings 58 or 60 depending upon the polarity of the slip ring 58 and 60 with respect to the polarity of the slip ring 56.

The SCRs 72, 74 and 76 are normally non-conductive. When the SCRs are non-conductive, the rotor windings are non-conductive and current cannot flow from the slip rings 56, 58 and 60. The SCRs 72, 74 and 76 include gates 72a, 72b and 720, respectively. As is well known, when the gate of an SCR is triggered and the anode is positive relative to the cathode, the SCR will conduct and will continue to conduct until the anode becomes negative with respect to the cathode. The SCR will then cease conducting and will not conduct again even if the anode becomes positive relative to the cathode unless a triggering pulse is applied to the gate terminal thereof.

It should be apparent that the slip rings 56, 58 and 60 will not be able to complete circuits therebetween unless at least one of the SCRs is conducting. When the SCRs are conducting, a current will flow from the slip rings through one of the lines 84, 86 and 88 through at least one of the SCRs through the resistor 64 and through at least one of the diodes 66, 68, back to one of the slip rings to thereby complete the circuit through the rotor windings so as to allow current induced in the rotor winding to flow through the rotor windings and through the load resistor 64. The primary or stator windings are preferably continuously energized and when induced current flows in the rotor windings the rotor will turn relative to the stator in a well-known manner. When the rotor windings are nonconductive, induced current will not flow therein even if the stator windings are energized and, therefore, the rotor will not turn.

The diodes 66, 68 and 70 are disposed in the circuit 62 and cooperate with the SCRs 72, 74 and 76 to form a full wave rectifying bridge when the SCRs are conducting. As is Well known, the full wave rectifying bridge will direct the current through the load resistor as it flows from the secondary windings. The current from the secondary windings flows through the SCR through the load resistor 64 and then through the diodes back to the secondary windings.

A firing module or circuit 90 is provided to trigger the gates of the SCRs. The firing circuit 90 preferably comprises a simple relaxation oscillator which would provide enough power at a sufficiently high frequency to make sure that any of the three SCRs would turn on at the beginning of a cycle. A line 92 isconnected to the firing module 90 and includes a switch 94 therein. The switch 94 is a pile height detector which detects variations in the height of the pile 16. When the height of the pile changes a predetermined amount, the switch 94 closes to energize the firing module 90. When the firing module 90 is energized, triggering pulses will be applied to the gates 72a, 72b and 720 of the SCRs 72,

74 and 76 respectively. When a triggering pulse is applied to the SCRs, the SCRs will be rendered conductive if the anode thereof is positive relative to the cathode thereof and circuits may be completed between the slip rings 56, 58 and 60 through the load resistor 64. This will cause the induced currents in the rotor field to flow and the rotor 54 will turn to effect turning of the shaft 38 and the worm gear 36 to thereby lower the platform 22.

The pile height detector switch 94 has a relay, not illustrated, associated therewith and when the switch 94 is closed, the relay will be energized to close hold-in contacts 96 which are disposed parallel to the switch 94. The switch 94 may be any suitable type of switch and in this case, when the pile height increases, a predetermined amount, the switch 94 will close and the firing module will be energized to energize the motor 40 to lower the platform 22. The hold-in contacts 96 keep the firing module 90 continuously firing while the platform 22 is lowered and the switch 94 is opened due to the decrease in height of the pile. It should be apparent that the switch 94 will open on an incremental downward movement of the platform 22. The hold-in contacts 96 enable the hoist to be lowered a predetermined amount when the switch 94 is opened due to lowering of the pile 16.

Means can be connected to the relay with which the contacts 96 are associated so that when the motor 40 lowers the platform 22 a predetermined incremental amount, the relay contacts 96 will be opened. The means may be in the form of a proximity switch, such as the one disclosed in the Reif et al. U.S. Pat. No. 3,035,835 entitled Pile Feeder" and assigned to the assignee of the present invention. Thus, after the platform 22 has been lowered a predetermined amount, the proximity switch will be energized to open the contacts 96. It should be apparent that when the contacts 96 are opened, the firing module will cease to fire and the SCRs 72, 74 and 76 will sequentially cease conducting when the anodes thereof become negative relative to the cathodes thereof. This will happen once during every cycle of the phase winding across which each SCR is connected and therefore, the rotor 54 of the motor 40 will stop rotating approximately one cycle after the firing module 90 has been de-activated.

The provision of a static switching circuit to render the rotor windings conductive or non-conductive of a wound rotor motor increases the longevity of the control for the hoist and less shut down time for the printing press is required than if a magnetic starter had been used. Moreover, because a wound rotor motor has been used, the speed of the motor goes up as the load in the platform 22 decreases, and therefore, the present system effectively provides high hoist speeds when there is no load on the platform 22 and it is desired to move the platform 22 at a very high speed, as when an empty skid is being positioned to initially receive sheets.

While the present invention has been illustrated as utilized in a pile delivering hoist, it should be obvious that the motor and circuitry could easily be employed in a pile feeder hoist to raise the hoist as sheets are fed therefrom or in similar load carrying machines.

From the foregoing, it should be apparent that a new and improved hoist for use with a printing press has been provided which is operable to raise or lower a pile of sheets so as to keep the top of the pile within a predetermined height. The hoist is raised or lowered by a wound rotor motor whose stator field is continuously energized and the motor is controlled in an intermittent mode by rendering the rotor windings alternately conductive and non-conductive to thereby control the flow of current which is induced in the rotor winding by the stator field.

What we claim is:

1. An apparatus for handling a pile of sheets whose height is varied by the feeding of sheets relative thereto and whose top is to be maintained between first and second horizontal levels, a motor for moving said pile from said first level to said second level, pile lever detecting means for sensing the level of said pile and energizing said motor when the top of said pile is at said first level and stopping said motor when the top of said pile is at said second level, the improvement wherein said motor is a wound-rotor motor having a primary winding and a secondary rotor winding, means for energizing said primary winding while said motor is operating and while stopped, and control means responsive to said detector means for rendering said secondary winding nonconductive at said second level and conductive at said first level to stop and start said motor while said primary winding remains energized, said control means including controlled rectifiers in series with said secondary windings for rendering said secondary windings alternately conductive and nonconductive, and triggering means responsive to said detector means for applying triggering signals to said rectifiers to enable said rectifiers to conduct to render said secondary windings conductive when said wound rotor motor is to operate.

2. An apparatus as defined in claim 1 wherein said triggering means comprises means for repeatedly applying pulses to said rectifiers in response to said detector means.

3. An apparatus as defined in claim 2 wherein said control means further includes means for rendering said triggering means inoperable to apply pulses to said rectifiers when the motor brings the top of the pile to said first level.

4. An apparatus as defined in claim 3 wherein said control means further includes diodes and a resistor, said diodes and said controlled rectifiers cooperating to form a rectifying bridge with said resistor connected across the output of said bridge.

5. An apparatus as defined in claim 4 wherein said detector means includes detector contact means in series with said triggering means, said detector contact means closing to energize said triggering means when the pile height reaches said second level and opening as the height of said pile varies from said second level toward said first level and wherein said means for rendering said triggering means inoperable to apply pulses to said controlled rectifiers includes second contact means disposed in a parallel circuit to said detector contact means, said second contact means closing in response to said detector contact means closing and opening in response to the pile being moved to said first level, said second contact means enabling said triggering means to remain energized as said motor moves the pile to said predetermined position and said detector contact means open as the height of the pile varies from said second level toward said position.