US3847251A

US3847251A - Control apparatus for a powered hoist

Info

Publication number: US3847251A
Application number: US00343047A
Authority: US
Inventors: J Binns; K Ellis; D Craven; P Maltby; S Glaze
Original assignee: Lucas Aerospace Ltd
Current assignee: Northrop Grumman Properties Ltd
Priority date: 1972-03-21
Filing date: 1973-03-20
Publication date: 1974-11-12
Anticipated expiration: 1991-11-12
Also published as: JPS4912559A; GB1419641A; FR2176986B1; FR2176986A1; DE2313893A1; IT979910B

Abstract

A control apparatus for a powered hoist which has a winch drum, a variable torque motor for driving the drum, and a brake for the drum, includes a device for detecting the load torque applied by the drum to the brake, when the latter is engaged, a circuit for increasing the torque of the motor and for releasing the brake only when the motor torque exceeds the load torque, and a circuit for varying the motor torque when the brake has been released.

Description

United StatesPatent [191 Maltby et al.

[ CONTROL APPARATUS FOR A POWERED HOIST [75] Inventors: Peter John Maltby, Codsall; Stanley George Glaze, Brierlcy Hill; Kenneth Harold Ellis, Wolverhampton; Donald Craven, Wolverhampton; John Michael Binns, Lichfield, all of England l73| Assignce: Lucas Aerospace Limited,

Birmingham, England [22] Filed: Mar. 20, 1973 [21] Appl. No.: 343,047

[ 30] Foreign Application Priority Data Mar. 21, 1972 Great Britain 13213/72 [52] US. Cl 187/29 R [51] Int. Cl. G05d 17/02 [58] Field of Search 187/29 1451 Nov. 12, 1974 [56] References Cited UNITED STATES PATENTS 3,244,957 4/1966 Spiess ct al. 187/29 X 3,486.10] 12/1969 Rulli 187/29 X 3,614,996 10/1971 Saito et a1 187/29 Primary ExaminerRobert K. Schaefer Assistant Examiner--W. E. Duncanson. Jr. Attorney, Agent, or l irmHolman & Stern [57] ABSTRACT 23 Claims, 3 Drawing Figures Z /r34 7/ y 160 I 173 l8 -'l l\ PATENIEDnnv 12 1974 SHEET 2 BF 3 p gngmi 3,847,251

MENTE" SHEET 30F 3 1 CONTROL APPARATUS FOR A POWERED HOIST This invention relates'to control apparatus for powered hoists and has an object to provide such a control apparatus in a convenient form.

' According to theinvention a control apparatus for a means for modifying the second torque when the brake has been released.

An example of the apparatus according to the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 showsas a block a pair of powered hoists together with associated control apparatus;

FIG. 2 is a diagram of a control apparatus, and

FIG. 3 is a circuit diagram of a part of the control apparatus.

Referring first to FIG. 1, a pair of powered hoist arrangements l0, 11 each comprises a winch drum 12 coupled by means of a shaft 13 to a gas turbine 14. A brake assembly 15 is mounted on the shaft 13 to arrest the drum in a manner later to be described. The turbines l4 and brake assemblies 15 are substantially as described in our co-pending application No. 1404/72. Brake assemblies 15 are spring-biased to arrest rotation of the drums 12 and are movable to release drums 12 by a gas pressure from a source 16 which also acts to drive turbines 14. Gas supply to each brake assembly 15 is under control of an associated solenoid valve 140 ('FIGJZ) responsive to electrical signals on lines 19 from-a pair of control apparatuses 17, 18 respectively associated with the hoist arrangements 10, 11.

Each turbine 14 includes a control valve operable by means of an electric motor to reverse the direction of rotation of the turbine and also to control the amount of gas flow through the turbine, and hence the turbine power output. Electrical signals to control the motors are supplied from the associated control apparatus via lines 20. The positions of the control valves are fed back to the associated control apparatus via lines 21.

Between each turbine 14 and the gas supply 16 is a shut-off valve 22 which is spring-biased to a shut position and which is operable to open by gas pressure from supply 16 under control of a solenoid valve 23. Valves 23 are responsive to signals on lines 24 from the associated control apparatus to open valves 22.

Each drum 12 is arranged so that associated cables 25 are laid up on drums 12 in a single layer only. The torque applied to each drum 12 by a given load W thus remains constant. The brake assemblies 15 respectively include a load-

sensing elements

26, 27 which are operable, when the associated brake assembly 15 is holding the drum 12, to supply a voltage signal corresponding to the torque on the drum 12 to the control apparatus via lines 27a.

Brake assemblies 15 also include microswitches 40, 41 (FIG. 2) operable, when the associated brake assembly 15 is holding its drum 12, to provide an electrical signal via line 28 to the control apparatus as soon 2 as the torque supplied by turbine 14 overcomes the torque due to load W.

Associated with each drum 12 are microswitches 29, 30 (FIG. 2) which apply voltage control signals-to the associated control apparatus via

respective lines

31, 32 when the drum 12 is at opposite extremes of its travel, that is when the cable 25 is respectively wound fully in and fully out. Potentiometers 183, 184 (FlG. 2) associated with the respective drums 12, provide signals on lines 33 indicating the positions of the drums l2, and hence the amounts by which cables 25 are wound in or out.

Each control apparatus l7, 18 includes a

respective control panel

34, 35 later to be described. Panels 34,

35 conveniently comprise hand-held units arranged so that control may be effected using one hand only.

The control apparatuses l7, 18 are interconnected in a manner later to be described, whereby both hoist arrangements 10, 11 may, if required, be controlled from a single one of the

panels

34, 35.

Each control apparatus 17, 18 incorporates a plurality of NAND gates whose input connections are such that both a +5 volt potential and an open circuit to these connections are logically equivalent to l and an earth potential applied to the connections is logically equivalent to 0. 1

Referring to FIG. 2, control apparatus 17 includes pair of switches 36, 37 which are respectively connected between positive and negative voltage sources and a common terminal 38. The winding of a potentiometer 39 is connected between terminal 38 and earth. Switches 36, 37 and potentiometer 39 form part of the control panel 34.

Apparatus 17 includes an end stop circuit 54 to which terminal 38 is connected. Circuit 54 includes a diode 42 having its cathode connected to terminal 38 and its anode connected via a resistor chain 43 and an inverter 44 to one input 45a of a NAND gate 45. An intermediate point of resistor chain 43 is connected via a diode 46 to earth so that a current can flow from earth via diode 42 to terminal 38 when the latter is at a negative potential. Input 45b of gate 45 is connected via line 32 and microswitch 30 to a +5 volt supply, and via a resistor 47 to earth.

Tenninal 38 is also connected to the anode of a diode 48 whose cathode is connected via a resistor chain 49 to one input 50a of a NAND gate 50. An intermediate point on resistor chain 49 is connected to earth viaa resistor 9. A second input 50b of gate 50 is connected via line 31 and microswitch 29 to a +5 volt supply, and also via a resistor 8 to earth.

The outputs of

NAND gates

45, 50 provide two of the inputs of a three input NAND gate 51, whose third input is provided in a manner later to be described. An inverter 52 has as an input the output of gate 51, the output of inverter 52 being connected to an output line 66 for the end stop circuit 54.

The wiper of potentiometer 39 is connected via a resistor 55 to the input terminal of an amplifier 56. The output tenninal of amplifier 56 is connected, via resistors 57, 58 in series, to the input terminal of a further amplifier 59. The common point 60 of resistors 57, 58 is connected, via

diodes

61, 62 respectively. to negative and positive reference voltages of predetermined values. The arrangement of

diodes

61, 62 is such that if the magnitude of the voltage at point 61 exceeds that of the reference voltages, current flows in the appropriate diode to maintain point 60 at the reference voltage.

The output terminal of amplifier 59 is connected to one input terminal of each pair of

differential amplifiers

63, 64 whose other input terminals are respectively connected to negative and positive voltages. The output terminals of

amplifiers

63, 64 are commonly connected to the third input of NAND gate 51 via a line 53.

Amplifiers

56,59, 63, 64 and the associated resistors and diodes form, in conjunction with end-stop circuit 54 a speed and direction selector circuit 65, having an output line 67 provided by the output of amplifier 59, and whose manner of operation is as follows. Assuming that the associated drum 12 is not at either end of its travel, switches 29, 30 are open. Then if switch 36 is closed to select an upward direction for the asso ciated hoist, a 1 will appear at input 50a of gate 50. The input of inverter 44 is earthed, i.e., volts providing a l at input 45a of gate 45. Since, however,

inputs

45b and 50b are both at 0, both

gates

45, 50 have a 1 output.

Movement of potentiometer 39 to select a hoist speed will cause

amplifiers

63, 64 to provide a positive output signal. All inputs to gate 51 will thus be at 1 and gate 51 will have a 0 output, which is converted to a l on line 66 by inverter 52. If however, switch 29 is closed indicating that the hoist is at the top limit of 50 to have an 0- output. Gate 52 will then provide a 0 output on line 66. M I

- In a'simil'ar manner gate 45 will have an 0 output when switches 30, 37 are both closed, and will have a 1 output in other conditions. A l signal thus appears on an output line from circuit 65 only when a speed and direction isfseleeted and the hoist is also free to move in theselected direction; If both switches 36, 37 are open, then both

gates

45, 50 will have a 1 output. lnthis circumstance a l on line 53 derived in a manner to'be described later, will result in a 1 output on line 66 from end stop circuit 54.

Lines 68, 69 are connected to the input terminals of

amplifiers

56,59 respectively. Lines 68, 69 carry signals which are more or less positive or negative when the selected direction is respectively up or down. The

- signal online 68 is not subjectto the speed limitation imposed by

diodes

61, 62.

Microswitch 40 is connected between a 5 volt supply and the signal line 28. A brake indicator latching circuit 70 comprises NAND gates 71, 72. Line 28 is connected to one input 71a of gate 71. Input 71a is also connected via a resistor to earth. The output of gate 71 is connected to an input 72a of gate 72, whose other input 72b is connected to a latching circuit reset line 73. The output of gate 72 is connected to an input 71b of gate 71. Microswitch 40 is operated by brake 15, when the latter is engaged with the associated winch drum 12, so that when a torque applied by the turbine 14 overcomes the torque due to load W, microswitch 40 opens.

Assume initially that there is an 0 on line 73 and that microswitch 40 is closed-The output of gate 72 will be at l and this last signal combines with the 1' from switch 40 to set the output of gate "71 to 0. The

state of circuit 70 does not, therefore, change if the signal on line 73 becomes l lf with signal on line 73 at l the microswitch 40 opens, the output of gate 71 becomes 1 and the output of gate 72 becomes 0. This last 0' output is also applied to gate 71 to latch the out; put of gate 72. Circuit thus has an 0 output only Switching circuit 78 forms part of a power-demand indicating circuit 79 and has a pnp transistor 80 with its base connected to connection 77, via a resistor 81. The emitter and collector of transistor 80 are respectively connected to a +5 volt supply and, via a resistor 82, to a 12 volt supply. The collector of transistor 80 is also connected via a resistor 83 to the gate of a field effect transistor 84. The source of transistor 84 is connected to earth. A positive potential at connection 77 cuts ofi' transistor 80, applying l2 volts to the gate of transis tor 84, which then becomes non-conductive. Similarly, an earth potential at connection 77 causes transistor 84 to conduct.

Circuit 79 also includes an amplifier 85 which receives an input from the load sensing device 26 on the associated brake assembly 15. The output terminal of amplifier 85 is connected to the drain of transistor 84. A tacho-generator 86 is responsive to the speed of the associated drum 12. The drain of transistor 84 and tacho-generator 86 are connected by

respective resistors

87, 88 to an output terminal 89 of circuit 79.

The output line'67 of circuit'65 is connected via resistors 90, 91 to the output terminal 89 of circuit 79. Terminal 89 also forms the input terminal of a position control circuit 93 for a synchro motor 94, which operates the direction and speed control valve in the turbine 14.

Circuit 93 includes an amplifier 95, to the input terminal of which the terminal 89 is connected. The out I common point of resistors 102, 103 is connected to earth via a switching circuit 104, identical with circuit 78 previously described.

A latching circuit 105, identical with latching circuit 70, is responsive both to the output from gate 75 and to the signal on line 73. A signal on a line 106 between the output of circuit and a control connection 107 for switching circuit 104 is thus maintained at l when there is an 0 output from gate 75.

A pair of

switches

110, 111 are included in the

respective control panels

34, 35.

Panels

34, 35 also respectively include

potentiometers

112, 113 and associated respective spring-loaded switches 114, 115. Switch 114 is connected between a +5 volt supply and an inverter 116 which forms part of a synchronising control circuit 117. The input of inverter 116 is also connected via a resistor to earth. Switch 114 and potentiometer 112 may be adjusted, in a manner later to be described, to obtain a condition in which both drums 12 are moved in unison but with different amounts of their associated cables wound out.

Switches

110, 111 are connected between a +5 volt supply and one input of a NAND gate 118 whose other input is connected to the output of inverter 116. The output of gate 118 is connected via inverter 119 to one input of aNAND gate 120. The output of gate 120 is connected to one input of a NAND gate 121 and the output of gate 121 is connected via an inverter 122 to a line 123 which provides an output connection for synchronising circuit 117 as a whole. Circuit 117 also includes an inverter 124 which is connected between output line 74 from latching circuit 70 and a second input of gate 120. A NAND gate 125 has one input also connected to the Output of gate 124 and a second input connected to the output of gate 118. A further output line 126 for circuit 117 extends from the output of inverter 119. Synchronising circuit 117 also includes a latching circuit 164 identical with circuit 70 and including

NAND gates

165, 166. One input of gate 165 is connected to earth via a resistor and also via one of lines 28 and microswitch 41 to a +5 volt supply. A reset line 167 for circuit 164 is connected to control apparatus 18 and corresponds to line 73 in apparatus 17. Signals on

lines

73, 167 are obtained in a manner later to be described.

The output of latching circuit 164 is connected via an inverter 129 to a third input of gate 120, and also via a line 163 to one input of a gate (not shown) in apparatus 18 and corresponding to gate 75 above described.

Line 123 is connected via an inverter 130 to one input of a NAND gate 131, whose other input is connected to the output line 66 from circuit 65. The output of gate 131 is connected via an inverter 132 to the control connection 133 of a switching circuit 134 which is identical to switching circuit 78. Circuit 134 is operable to connect the common point of resistors 90, 91 to earth, and circuit 134, together with inverters 130, 132 and gate 131, comprises an output control circuit 135 for signals on line 67 from speed selection circuit 65. End stop circuit 54 and circuit 135 together comprise a switching arrangement for isolating a speed and direction demand signal from the position control circuit 93.

A solenoid 140 for the gas control valve for the brake is responsive to a brake control circuit 141, comprising a NAND gate 142, an inverter 146, a latching circuit 147, identical with circuit 70, and power stage switching circuit 148, identical with circuit 78. Control circuit 141 has as its inputs the

lines

66 and 123 and a third input provided by a differential amplifier 145 responsive to the output of the tacho-generator 86. Amplifier 145 is biased so as to provide a 1 output when the drum 12 is stopped, and an 0 output when drum 12 is rotating.

A reset circuit 128 is also responsive to an output signal from amplifier 145 and comprises

NAND gates

144, 154, 155, 157 159, and

inverters

143, 153, 158, 160, 169.

Line 66 is connected to one input of gate 142 and via inverter 143 to one input of gate 144. Gates 142, 144 also have inputs provided by differential amplifier 145. Line 123 is connected via inverter 146 to a third input of gate 142. The output of gate 142 is connected, via latching circuit 147, to a control connection of the power stage 148. Stage 148 is in series with relay contacts 149 to control current flow from a 28 volt supply through solenoid 140. As above described the turbine 14 includes a gas shut-off valve 22. The shut-off valve 22 is controlled by a servo-valve 23 operable by a solenoid 150 which is connected in parallel with solenoid and stage 148. Solenoid is not, however, responsive to control circuit 141, but to operation of relay contacts 149 as a result of operation of a relay 151 by either of a pair of emergency stop switches 138, 139 on the

respective panels

34, 35.

The output of gate 144 is connected via inverter 153 to one input of each of gates 154, 155. Output line 126 from circuit 117 is connected to the other input of gate 155, to one input of gate 157 and via inverter 158 to an input of gate 154. The outputs of

gates

154, 155, 157 provide inputs for gate 159. A further input for gate 159 is provided from a +5 volt supply when either of

switches

138, 139 in

panels

34, 35 respectively are made. The output of gate 159 is connected via inverter 160 to the reset line 73, which forms an output line from reset circuit 141. Line 73 provides an input into one gate of each latching

circuit

70, 105 and 147, as described above.

A switching circuit 161, identical to

circuits

78, 104, 134 is operable, when an earth potential is applied to its control connection 162, to connect the common point of

resistors

98, 99 to earth. Connection 162 is connected to the output of inverter 132 in circuit 135. A line 168 is connected, via an inverter 169 to a second input of gate 157. Line 168 is connected, in apparatus 18, to the output of a gate which corresponds to gate 144 as described above. The output gate 144 is similarly connected, via a line 179 to an inverter in apparatus 18 corresponding to inverter 169.

The parts of the control apparatus 17 so far described are these necessary to effect control of the associated hoist arrangement 10 only, by means of the control panel 34, in which cases switches 110, 111 will not be made, and there will always be a 0 on line 126. Before starting operation the amplifier 145 has a 1 output, and if speed and direction have not been selected there is a 0 on line 66 from circuit 65. Both inputs of gate 144 are therefore at l and the resulting 0 at the output is inverted to provide a l at one of the inputs of gate 154. The other input of gate 154 is also at l as a result of the inverted 0 on line 126. The output of gate 154 is thus at 0 producing a l at the output of gate 159 and a 0 on reset control line 73. The outputs of all the latching

circuits

70, 105, 147 are thus at l, irrespective of the states of the other inputs of these latching circuits.

The 0 on line 66 causes the output of gate 142, and hence that of latching circuit 147, to be 1 causing the switching circuit 148 to de-energise brake solenoid 140. The brake assembly 15 is thus holding the shaft 13.

If, however, there is a l on line 66 and an-O on line 126, all the inputs of gate 159 will be at l The signal on line 73 is thus, in this condition, not affected by the signal on line 168 from apparatus 18. If, however, there is a l on line 126, i.e., synchronised operation selected by either of

switches

110, 111 and switches 114, 115 are in their normally open condition, the output of gate 157 will be 1 only if the input to gate 169 is also 1. The input to gate 169 is 1' only when the output of the gate in apparatus 18, corresponding to gate 144', is 1, that is when the output of the end stop circuit in apparatus 18 is 1. When synchronised operation is selected, i.e., when there is a l on line 126, the reset circuit in apparatus 18 will have a 1 output only when end stop circuit 54 in apparatus 17 has a 1 output.

Selection of a speed and direction provides a l on line 66 which, by applying an to one input of gate 144, causes the output of the latter to become 1. An 0 is thus applied to one input of gate 154, causing its output to become 1. The states of

gates

155, 157 remain unchanged, and the output of gate 159 therefore becomes 0. The signal on line 73 is thus l, whereby the states of latching circuits70, 105, 147, may be changed.

Assuming initially that the brake assembly is hold ing drum 12 against the load W, there is a l on line 74 from latching circuit 70 as above described. This l is inverted and causes gate 125 to have a 1 output. The 0 remaining on line 126 is inverted by inverter 120, and the two 1 inputs to gate 121 cause the latter to have an 0 output which is inverted to provide a 1 on line 123. An 0 is applied to one input of gate 131, and the resultant 1 output is inverted to cause switching circuit 134 to earth the common point of resistors 90, 91. A speed and direction demand signal from circuit 65 is thus earthed. The common point of

resistors

98, 99 is also earthed by circuit 61.

The l on each of

lines

66, 74 causes the output of is thus applied to terminal 89 of position control circuit 93. Since the common point of

resistors

98, 99 is *earthed the torque load signal appearing at terminal 89 is routed to amplifier 97. The 0 at the output of gate 75 also causes latching circuit 105 to maintain a 0 at the control connection of switching circuit 104, earthing the common point of resistors 102, 103. Capacitor 101 thus provides the feedback path for amplifier 97, causing the latter to act as an integrator. The input signal to amplifier 100 thus increases at a rate dependent on the magnitude of the torque sensed by element 26. Motor 94 thus operates to increase the torque delivered by turbine 14.

When the turbine torque exceeds the torque due to load W, brake assembly 15 is rotated against the load by shaft 13, and microswitch 40 becomes open circuit. The resultant 0 at the input of latching circuit 70 causes an 0 to be set on line 74, and also causes the signals at both inputs of gate 125 to become l The resulting O on one input of gate 121 places an 0 on line 123. All inputs to gate 142 then become l and circuit 147 latches an 0 on to the switching circuit 148, energising solenoid 140 and releasing the brake assembly 15 from the shaft 13.

The 0 on line 74 is inverted by gate 75 and is applied to latching circuit 105, which does not, however, change its state. Switching circuit 104 thus remains in its closed circuit condition and amplifier 97 continues to integrate. The 1 from gate 75 is again inverted and switching circuit 78 earths the output from load sensing element 26.

The 0 on line 123 causes both inputs to gate 131 to be 1 and the resulting 1 output from inverter 132 places switching circuits 134, 161 in their open circuit condition. The speed and direction demand signal from circuit 65 can thereby pass to terminal 89 to be summed with the output of tacho-generator 86 to provide a speed error signal. The amplified signal from terminal 89 can also pass via

resistors

98, 99 to amplifier 100. A potentiometer 181 is responsive to the position of the air control valve for turbine 14 in hoist arrangement 10. The voltage on the wiper of potentiometer 181 is supplied via line 21 and a resistor to the input of amplifier 100.

The input signal to amplifier is thus a positionerror signal for the air control valve.

In the absence of a speed error signal at terminal 89 the integrating amplifier 97 has an output signal which remains at the level at which load torque was overcome. In this condition the motor 94 has positioned the air control valve so the turbine torque balances load torque and the hoist is stationary. A speed-error signal at terminal 89, corresponding to a requirement for upward movement of the load, causes the output signal from amplifier 97 to increase at a rate corresponding to the magnitude of the speed-error signal. This increasing signal is summed at the input of amplifier 100 with the output of amplifier 95, and with the feedback signal from potentiometer 181, to provide a fresh position-error signal which reduces to zero as the air control valve is moved by motor 94.

A speed-error signal corresponding to a downward movement of the load similarly causes the input signal to amplifier 100 to be reduced, and motor 94 moves the air control valve so that the torque output of the turbine falls below that imposed by the load W. The winch is thus rotated by the load against the reduced lifting torque of the turbine. v

If there is no external load on the cable, the weight of the cable which remains off the drum, even in the wound in position, is sufficient to provide a torque load signal at terminal89. The turbine torque thus increases until the brake is released, as before. The voltage level at the output of integrating amplifier 97 is nevertheless small and a downward speed-error signal causes motor 94 to drive the gas control valve to reverse the direction of rotation of the turbine.

If the turbine is stopped, either by movement of potentiometer 39 to a zero-speed position or by opening switches 36, 37, an 0 appears at the output of end-stop circuit 54 and is applied via line 66 to reset circuit 128, causing the signal on line 73 to change from l to 0. The 0 on line 73 is applied to one input of each of latching

circuits

70, 105, 148 whose outputs are then set to l irrespective of the signals at the other inputs of these latching circuits. The 1 output of circuit 70 is applied to synchronising circuit 117 and causes the signal on line 123 to change from 0 to l. The l on line 123 and the O on line 73 are each sufficient to cause brake control circuit 141 to apply the brake. At the same time the output of inverter 76 is set to 0 and switching circuit 78 conducts, earthing the output of load-sensing element 26. The l on line 123 operates via output control circuit 135 to cause switching circuit 134 to earth the junction of resistors 90, 91, and also operates to cause switching circuit 161 to earth the junction of the

resistors

98, 99. Finally, the l output from latching circuit renders switching circuit 104 non-conductive, and amplifier 97 ceases to act as an integrator. The signal level from amplifier 97 thus disappears. Apparatus 17 is thus set to its pre-start condition, from which it cannot depart until there is once again a 1 from end-stop circuit 54.

If, while hoist arrangement 10 is running, either of emergency stop switches 138, 139 is opened, relay 151 is de-energised and contacts 149 open. Solenoids 150 and 140 are in consequence de-engergised and the brake is applied. At the same time the input to gate 159 causes an 0 to be set on line 173. The output of all latching

circuits

70, 105, 147 thus becomes l and the apparatus is reset, as before to its pre-start condition.

The input of amplifier 56 is connected via a resistor 170 to earth via a switching circuit 171 which is identical to circuit 78. The control connection of circuit 171 is connected to a volt supply via the

switches

110, 111. The common point of resistor 170 and circuit 171 is also connected via a resistor 172 to a line 173 which extends to the wiper of a speed demand potentiometer 174 forming part of control panel 35. Apparatus 18 is identical to apparatus 17 as above described, except that apparatus 18 has no equivalent of synchronising control circuit 117.

A synchronising circuit 180 is connected to apparatuses 17, 18, to control

panels

34, 35 and via lines 33 to the potentiometers 183, 184 respectively associated with the drums 12.

In the convention of the diagram of FIG. 2 upward movement of the wipers of potentiometers 183, 184 corresponds to rotation of the associated drums to provide upward movement of a load thereon. The wiper potentiometer 183 is connected via a resistor 185,an inverting amplifier 186 and a further resistor 187 to a summing junction 188. The wiper of potentiometer 184 is connected via a resistor 182 to junction 188. The

wipers

112a, 113a of

potentiometers

112, 113 are also connected to junction 188.

Wipers

112a, 113a are biased towards the mid-points of their respective tracks. Associated with

wipers

112a, 113a are latching means indicated at 189, 190, for retaining these wipers in required positions. Operation of the latching means 189, 190 to disengage the

respective wipers

112a, 113a causes'the associated switches 114, 115 to be closed.

Summing junction 188 provides an input connection for an amplifier 191 whose output terminal is connected to earth via a resistor 192 and a switching circuit 193, identical to switching circuit 78. The common point of resistor 192 and circuit 193 is connected via a line 206 and a resistor 207 to the input of amplifier 59. The output terminal of amplifier 191 is also connected to earth via a resistor 194, an inverting amplifier 195 a further resistor 196 and a further switching circuit 197. The common point of resistor 196 and circuit 197 is connected via a line 208 to a part of control apparatus 18 corresponding to resistor 207 and amplifier 59.

Load sensing element 26 is connected via an amplifier 198 to one input of a differential amplifier 199. Load sensing element 27, associated with hoist arrangement l l, is connected via an amplifier 200 to the other input of amplifier 199. Amplifier 199 is such that when the loads are equal or that sensed by element 26 is the greater there is, an 0 at the output of amplifer 199, and when the load sensed by element 27 is the greater there is a l at the amplifier output.

The output of amplifier 199 is connected to one input of a NAND gate 201 and via an inverter 202 to one input of a NAND gate 203. The other inputs of gates 201', 203 are connected to the +5 volt supply via

switches

110, 111. The output of gate 201 is connected via an inverter 204 to the control connection of switching circuit 193. The output of gate 203 is connected via an inverter 205 to the control connection of switching circuit 197.

A switching circuit 209 forming part of control apparatus 18 has its control connection connected to the +5 volt supply via

switches

110, 111. A pair of resistors 210, 211 also form part of apparatus 18 and are connected in series in a line 212 between the wiper of potentiometer 39 and the input connection of an amplifier 213 which also forms part of apparatus 18 and corresponds to amplifier 56 in apparatus 17.

Resistors

170, 172, 210, 211 have the same value. This value is twice that of resistors 55 in apparatus 17 and also twice that of a resistor 214 at the input of amplifier 213 in apparatus 18. The impedance between the wiper of potentiometer 39 and the amplifier 56 is the same as that between potentiometer 39 and amplifier 213, when switching circuit 171 is open. Similarly the impedance between potentiometer 171 and

amplifiers

56 and 213 are the same when switching circuit 209 is open.

In use, with either one of

switches

110, 111 made, a 1 is applied to one input of gate 118. If switches 114, are open, there is also a 1 at the other input of gate 118. The resulting 0 output from gate 118 causes the output of gate 125 to be at l even after the torque load on hoist arrangement 10 has been overcome and microswitch 40 has opened. Since at least one of the inputs of gate 121 must be at 0 if there is to be an 0 on line 123 to allow the hoist to start, all the inputs to gate must be at l This last condition will only obtain when the output of latching circuit 164 is at 0, i.e., when the torque load on hoist arrangement 11 has also been overcome.

Assume, in use, thatboth hoist arrangements 10, 11 are to be controlled from control panel 34, and assume also that the load W on hoist arrangement 11 is the heavier. There will then be, as above described, a 1 output from the amplifier 199. Both inputs of gate 201 are thus at 1 and the resulting l at the control connection of switching circuit 193 causes the latter to be open-circuit. The l output from amplifier 199 is inverted by inverter 202 and causes the output of inverter 205 to beat 0. Switching circuit 197 thus earths the output of amplifier 95, and there is no signal on line 208. A signal from amplifier 191 is thus applied via line 206, and resistor 207 to the input of amplifier 59 in apparatus 17.

When

switch

110 or 111 is closed, both switching circuits 171, 209 are rendered open-circuit. The inputs of

amplifiers

56 and 213 in apparatus 17 and 18 respectively are thus inter-connected via

resistors

170, 172, 210, 211. A speed and direction selected on either of

control panels

34, 35 will be applied to both of control apparatuses 17, 18. As described above with reference to the operation of end-stop circuit 54, even if both direction selection switches on the associated

panel

34 or 35 are open, a speed and direction signal at the inputs of

amplifiers

56, 213 applies a l to line 53 and to the corresponding line in apparatus 18, thereby causing the output signal from the associated end-stop circuits to be 1. Neither of hoist arrangements 10, 11 will, however, start up until the torque load on both has been overcome, as described above in connection with the synchronising circuit 117 of apparatus 17.

With both hoists operating to lift their loads, and the load on hoist arrangement 1 1 being the heavier, it is to be expected that drum 12 in arrangement 10 will lead the drum of arrangement 11. The wiper of potentiometer 183 thus becomes more positive than that of potentiometer 184. The input of amplifier 191 becomes negative and a negative signal is applied via line 206 to the input of amplifier 59. This negative signal opposes the signal from control panel 34 by an amount dependent on the amount by which the drum arrangement 10 leadsthat of arrangement 11.

Similarly, if arrangement 10 lags behind arrangement 11, the'speed demand signal from control panel 34 is enhanced by the signal on line 206. It will be understood thatif the loads are being lowered the operation of the apparatus is substantially the same, the signal on line 206 opposing any tendency of hoist arrangement 10 to lag or lead arrangement 11. It will also be understood that if the load arrangement on 10 is the same as that on arrangement 11 or is the heavier, signals are then applied via line 208 to apparatus 18 to reduce any tendency of hoist arrangement 11 to lag or lead arrangement 10. In general the arrangement having the lighter load is caused to follow that having the heavier load. With loads swinging the heavier load may alternate between arrangement 10, 11 and the functions of master and slave apparatus then alternate between apparatus 17 and apparatus 18 under control of switching circuits 193, 197.

If when arrangements 10, 11 are being operated in synchronism, it is required that, say the drum 12 in arrangement 10 is to be moved with respect to the other drum, this may be effected by adjustment of either potentiometer 112 or potentiometer 113 in the

respective control panels

34, 35. Disengagement of the latching means '189 to move potentiometer 112 causes switch 114 to be made. The resulting at the output of inverter 116 causes the output of gate 118 to be l The effect on circuit 117 is thus as if

switches

110, 111 were not closed, while switch 114 or switch 115 are closed.

' lf wiper 1 12a is moved a desired amount from its central position the associated interlock 189 is then released to maintain the position of wiper 112a, thereby re-opening switch 114. As a result of movement from its central position wiper 112a cause a biasing voltage to be applied to junction 188. If the load on hoist arrangement 11 is the greater, then this biasing voltage is applied to the'input of amplifier 59 in apparatus 17. If the biasing voltage is positive then, when the hoist arrangements are started by selection of a speed and direction by either of

panels

34, 35, this positive bias will increase the upward speed of hoist arrangement until balanced by the increasing negative bias dueto the difference in the positions of potentiometers 183, 184 after which both hoists move in synchronism. Similarly, if the load on arrangement 10 is the heavier, then a positive voltage from potentiometer 112 applies a negative bias via amplifier 195 and switching circuit 197 to the input of an amplifier in apparatus 18, corresponding to amplifier 59 in apparatus 17. Once again hoist arrangements 10, 11 are driven at different speeds until the signal at junction 188 is zero, both hoists moving in synchronism thereafter.

We claim:

l. A control apparatus for a powered hoist having a winch drum, a motor capable of variable output for driving the drum and a brake for the drum, said control apparatus comprising means for detecting a first torque applied by the drum to the brake when the latter is en gaged to arrest the drum, control means for causing a second torque supplied by said driving motor to be increased, brake control means responsive to movement of said drum by said second torque, said brake control means for releasing said brake only when the second torque exceeds the first torque, and further control means, operative only when the brake has been released, for modifying the second torque.

2. A control apparatus for a powered hoist having a winch drum, a motor capable of variable output for driving the drum and a brake for the drum, said control apparatus comprising means for generating a first electrical signal dependent on a first torque which is applied by the drum to the brake when the latter is engaged to arrest the drum, means responsive to the magnitude of said first electrical signal to generate a second electrical signal, said motor supplying a second torque, means for increasing said second torque at a rate dependent on the magnitude of said second electrical signal, means for releasing said brake only when the second torque exceeds the first torque, and furthercontrol means, operative only when the brake has been released, for modifying the second electrical signal.

3. An apparatus as claimed in claim 2 which includes a synchro motor responsive to said second electrical signal to vary said second torque from said driving motor.

4. An apparatus as claimed'in claim 3 in which said means for releasing the brake comprises afirst'switching means, operable by the brake, when a part-thereof is urged against said first torque by said second torque, to provide a third electricalsignal, said brake being released in response to said third electrical signal.

5. An apparatus as claimed in claim 4 which includes second switching means responsive to said third electrical signal to provide a fourth electrical signal, and an electro-magnet device responsive to said fourth electrical signal to release said brake. f

6. An apparatus as claimed in claim 5 which'includes third switching means responsive to said third electrical signal to isolate'said first electrical signal from said second electrical signal generating means.

7. An apparatus as claimed in claim 5 which includes means for generating a fifth electrical signal dependent on the rotational speed of said drum, said means for generating the second electrical signal being responsive to said fifth electrical signal. r

8. An apparatus as claimed in claim 7 in which said means for modifying the second torque includes means for generating a sixth electrical signal dependent on a desired speed and direction-of rotation of said drum, said means for generating the second electrical signal being responsive to said sixth electrical signal.

9. An apparatus as claimed in claim 8 which includes fourth switching means operable when said drum has reached a permitted limit of its rotation in either direction, for isolating said sixth electrical signal from said second electrical signal generating means.

' 10. An apparatus as claimed in claim 9 in which said second electrical signal generating means includes means for summing said fifth and sixth electrical signals and a first amplifier responsive to the output of said summing means to provide an eighth electrical signal.

11. An apparatus as claimed in claim in which said second electrical signal generating means includes a further amplifier responsive to said eighth electrical signal and to the output of said summing means to provide said second electrical signal.

12. An apparatus as claimed in claim 11 which includes means for generating a feedback signal dependent on the rotational position of said synchro motor, said further amplifier also being responsive to said feedback signal.

13. An apparatus as claimed in claim 12 which includes fifth switching means responsive to said third electrical signal to isolate said further amplifier from the output of said summing means, whereby said further amplifier is responsive only to said eighth electrical signal only when said first switching means is not operated by said brake.

14. An apparatus as claimed in claim 11 which includes a feedback arrangement associated with said first amplifier to cause the latter to operate as an integrator, and sixth switching means responsive to operation of said sixth electrical signal generating means and to operation of said fourth switching means to render said feedback arrangement operative, whereby said first amplifier acts as an integrator when said sixth electrical signal is present and when said drum is not at one of its limits of angular rotation.

15. An apparatus as claimed in claim 14 which includes a logic circuit responsive to said fifth electrical signal and to operation of said fourth switching means and said sixth electrical signal generating means, to generatev a ninth electrical signal, whereby said ninth electrical signal is present only in the presence of said sixth electrical signal and when said drum is not at one of its limits of rotation, and a plurality of latching circuits responsive to said ninth electrical signal to cancel said third and fourth electrical signals and to cause said sixth switching means to render said feedback arrangement inoperative.

16. An apparatus as claimed in claim 15, in combination with a further, similar, control apparatus for a further powered hoist, similar to the first-mentioned hoist, and an interconnection arrangement energisable to cause said control apparatus to coact, whereby the second torque supplied by both of said driving motors may be modified by the torque modifying means of one of said control apparatuses.

17. A combination as claimed in claim 16 which includes seventh switching means operable to provide a tenth electrical signal, said interconnection arrangement being responsive to said tenth electrical signal to cause said control apparatuses to coact.

18. A combination as claimed in claim 17 in which said interconnection arrangement includes a second logic circuit responsive to said third electrical signal and to said tenth electrical signal to provide an eleventh electrical signal, said fourth switching means and a corresponding switching means in said further control apparatus being responsive to said eleventh electrical signal, whereby, when said seventh switching means is operated, and said first switch means and a corresponding switching means in said further apparatus is operated, said sixth electrical signal, and a corresponding arrangement inoperative.

20. A combination as claimed in claim 19 in which said interconnection arrangement includes first and second means responsive to the rotational positions of the respective drums to provide thirteenth and fourteenth electrical signals, second summing means responsive to said thirteenth and fourteenth electrical signals to provide a fifteenth electrical signal, and first and second modifying means for respectively modifying said sixth electrical signal, and a corresponding signal in said further control apparatus, in accordance with said fifteenth electrical signal.

21. A combination as claimed in claim 20 which includes means for generating a sixteenth electrical signal dependent on the torque applied by the drum of said further hoist to the brake thereof when the latter is engaged, and ninth and tenth switching means responsive to said first and sixteenth electrical signals and to said tenth electrical signal and respectively operable to isolate said fifteenth electrical signal from said sixth electrical signal and from the corresponding signal in said further control apparatus.

22. A combination as claimed in claim 20 which includes means for modifying said thirteenth and fourteenth electrical signals in accordance with a desired difference in the rotational positions of said drums.

23. A combination as claimed in claim 17 which includes means for interconnecting said sixth electrical signal generating means and the corresponding generating means in said further control apparatus, and eleventh switching means responsive to said tenth electrical signal to render said interconnecting means inoperative.

Claims

1. A control apparatus for a powered hoist having a winch drum, a motor capable of variable output for driving the drum and a brake for the drum, said control apparatus comprising means for detecting a first torque applied by the drum to the brake when the latter is engaged to arrest the drum, control means for causing a second torque supplied by said driving motor to be increased, brake control means responsive to movement of said drum by said second torque, said brake control means for releasing said brake only when the second torque exceeds the first torque, and further control means, operative only when the brake has been released, for modifying the second torque.

2. A control apparatus for a powered hoist having a winch drum, a motor capable of variable output for driving the drum and a brake for the drum, said control apparatus comprising means for generating a first electrical signal dependent on a first torque which is applied by the drum to the brake when the latter is engaged to arrest the drum, means responsive to the magnitude of said first electrical signal to generate a second electrical signal, said motor supplying a second torque, means for increasing said second torque at a rate dependent on the magnitude of said second electrical signal, means for releasing said brake only when the second torque exceeds the first torque, and further control means, operative only when the brake has been released, for modifying the second electrical signal.

4. An apparatus as claimed in claim 3 in which said means for releasing the brake comprises a first switching means, operable by the brake, when a part thereof is urged against said first torque by said second torque, to provide a third electrical signal, said brake being released in response to said third electrical signal.

5. An apparatus as claimed in claim 4 which includes second switching means responsive to said third electrical signal to provide a fourth electrical signal, and an electro-magnet device responsive to said fourth electrical signal to release said brake.

6. An apparatus as claimed in claim 5 which includes third switching means responsive to said third electrical signal to isolate said first electrical signal from said second electrical signal generating means.

7. An apparatus as claimed in claim 5 which includes means for generating a fifth electrical signal dependent on the rotational speed of said drum, said means for generating the second electrical signal being responsive to said fifth electrical signal.

8. An apparatus as claimed in claim 7 in which said means for modifying the second torque includes means for generating a sixth electrical signal dependent on a desired speed and directioN of rotation of said drum, said means for generating the second electrical signal being responsive to said sixth electrical signal.

10. An apparatus as claimed in claim 9 in which said second electrical signal generating means includes means for summing said fifth and sixth electrical signals and a first amplifier responsive to the output of said summing means to provide an eighth electrical signal.

11. An apparatus as claimed in claim 10 in which said second electrical signal generating means includes a further amplifier responsive to said eighth electrical signal and to the output of said summing means to provide said second electrical signal.

15. An apparatus as claimed in claim 14 which includes a logic circuit responsive to said fifth electrical signal and to operation of said fourth switching means and said sixth electrical signal generating means, to generate a ninth electrical signal, whereby said ninth electrical signal is present only in the presence of said sixth electrical signal and when said drum is not at one of its limits of rotation, and a plurality of latching circuits responsive to said ninth electrical signal to cancel said third and fourth electrical signals and to cause said sixth switching means to render said feedback arrangement inoperative.

18. A combination as claimed in claim 17 in which said interconnection arrangement includes a second logic circuit responsive to said third electrical signal and to said tenth electrical signal to provide an eleventh electrical signal, said fourth switching means and a corresponding switching means in said further control apparatus being responsive to said eleventh electrical signal, whereby, when said seventh switching means is operated, and said first switch means and a corresponding switching means in said further apparatus is operated, said sixth electrical signal, and a corresponding signal in said further apparatus, are respectively isolated from said second electrical signal generating means and from a corResponding generating means in said further apparatus.

19. A combination as claimed in claim 18 which includes eighth switching means, corresponding to said first switching means and operable by the brake of said further powered hoist to provide a twelfth electrical signal, and in which said second logic circuit includes a further latching circuit responsive to said ninth and twelfth electrical signals to render said interconnection arrangement inoperative.