ADJUSTABLE VOLTAGE THYRISTOR-CONTROLLED HOIST CONTROL FOR A DC MOTOR

• US 3,746,954 A
• Filed: 09/17/1971
• Issued: 07/17/1973
• Est. Priority Date: 09/17/1971
• Status: Expired due to Term

• Current Assignee: Asa H. Myles, Fred Erb
• Original Assignee: Asa H. Myles, Fred Erb
• Inventors: Myles, Asa H., Erb, Fred
• Primary Examiner(s): Gilheany, Bernard A.
• Assistant Examiner(s): Duncanson, Jr., W. E.
• Application Number:
  US05/181,515
• Time in Patent Office: 669 Days
• Field of Search: 318/258,261,269,274,341,342,344,375,247,248
• US Class Current: 318/247
• CPC Class Codes: B66C 13/24 by dc motors
• CPC Class Codes: H02P 7/281 the DC motor being operated in four quadrants
• CPC Class Codes: H02P 7/298 controlling armature and field supply
• CPC Class Codes: Y10S 174/16 in a motive power system, e.g. electric motor control system

Abstract

A direct current series motor is powered by adjustable voltage from an alternating current source. The motor is series connected during hoisting and powered by a single AC-DC converter, and shunt connected during lowering with a second AC-DC converter supplying the field. An isolation resistor permits dynamic lowering and provides emergency dynamic braking even with the independently energized armature and field. A teaser field resistor which prevents overspeeding when the motor is hoisting a light load is automatically disconnected while the motor is hoisting a sufficiently heavy load and is reconnected if the load becomes too small. During lowering, a dynamic braking resistor may be removed from across the armature without any material change in motor speed.

Claims

1. A control system for operating a direct current motor having an armature and a series-wound field fRom an alternating current source, said system comprising a motor having an armature and a series-wound field, first and second AC-DC converter means each having control and power input terminals and output terminals, said source being electrically connected to the power input terminals of the first and second converter means, master switch means selectively operable in a first range for controlling operation of the motor in one direction of rotation and a second range for controlling operation of the motor in an other direction of rotation, signal means producing a voltage of a first polarity when the master switch means is in its first range and producing a voltage of a second polarity when the master switch is in its second range, reference control means electrically connected to the signal means and to the control input terminals of the first and second converter means and responsive to a voltage of the first polarity from the signal means to produce a direct current output from only the first converter means and responsive to a voltage of the second polarity from the signal means to produce direct current outputs from both the first and the second converter means, means serially connecting the armature and the field across the output terminals of the first converter means when the master switch means is in its first range, means connecting the armature across the output terminals of the first converter means and connecting the field across the output terminals of the second converter means when the master switch means is in its second range, and an isolation resistor serially connected between the armature and the field so that excitation of the field is related to the voltage across the armature when the master switch means is in its second range.

2. A control system as in claim 1 wherein said means serially connecting the armature and the field across the output terminals of a first converter means and said means connecting the armature across the output terminals of the first converter means and connecting the field across the output terminals of the second converter means maintains the polarity of the voltage impressed on the field the same for both ranges of the master switch and causes the voltage impressed on the armature to be of one polarity in the first range of the master switch and of a different polarity in the second range of the master switch.

3. A control system as in claim 1 wherein said first range of said master switch means is a non-overhauling range in which a load on the motor is normally non-overhauling and said second range of said master switch means is an overhauling range in which the load on the motor is normally overhauling.

4. A control system as in claim 1 wherein said system is for driving a crane hoist, said first range of said master switch means is a hoisting range, and said second range of said master switch means is a lowering range.

5. A control system as in claim 4 including an overhoist limit switch having normally closed limit switch contacts and wherein said means serially connecting the armature and the field across the output terminals of the first converter means when the master switch mean is in its hoisting range includes the limit switch contacts and wherein said means connecting the armature across the output terminals of the first converter means and connecting the field across the output terminals of the second converter means when the master switch means is in its lowering range is independent of the limit switch contacts.

6. A control system as in claim 1 and including an electromagnetically-released brake means having a release winding connected serially with said armature and field and energized by the direct current output of only said first AC-DC converter means when said master switch means is in its first range and by the direct current outputs of both said first and second AC-DC converter means when said master switch means is in its second range.

7. A control system as in claim 1 wherein said Master switch means includes means for changing the voltage of said signal means, and wherein said reference control means includes means responsive to a change in the voltage of the first polarity from the signal means to produce a change in the direct current output of said first AC-DC converter means and means responsive to a change in the voltage of the second polarity from said signal means to produce a change in the direct current outputs of both said first and second AC-DC converter means.

8. A control system as in claim 1 and including a teaser field resistor, switching means for connecting the teaser field resistor across the armature, and current sensitive means for operating the switching means at a predetermined magnitude of the direct current output of the first converter means while the master switch is in the first range, the teaser field resistor being connected across the armature at low magnitudes of the direct current output and being disconnected from the armature at high magnitudes of the direct current output.

9. A control system for operating a direct current motor having an armature and a series-wound field from an alternating current source, said system comprising a motor having an armature and a series-wound field, AC-DC converter means having control and power input terminals and output terminals, said source being electrically connected to the power input terminals of the converter means, master switch means having an operating range for controlling operation of the motor, signal means for producing a voltage of a selected polarity and of a magnitude controlled by said master switch means, reference control means electrically connected to said signal means and to the control input terminal on the converter means and responsive to the magnitude of the voltage from said signal means to control a direct current output from the converter means at said output terminals, means serially connecting the armature and the field across said output terminals, a teaser field resistor connected across the armature, and current sensitive means for disconnecting the teaser field resistor at a predetermined magnitude of the direct current output of the converter means;

said current sensitive means comprising current-indicating means interposed in the motor circuit for producing a current-magnitude signal indicating the magnitude of direct current output of said AC-DC converter means, and load sensing means connected to said current-indicating means and responsive to a first predetermined magnitude of said current-magnitude signal to disconnect said teaser field resistor and responsive to a second predetermined magnitude of said current-magnitude signal to connect said teaser field resistor;

said load sensing means comprising biasing means providing a biasing signal, comparison means connected to said current-indicating means for comparing said current-magnitude signal to said biasing signal and producing a voltage of one polarity if said current-magnitude signal is of greater magnitude than the biasing signal and of an other polarity if said current-magnitude signal is of smaller magnitude than the biasing signal, time delay means connected to said comparison means and providing an output after a time delay, and relay means responsive to the output of the time delay means for selectively connecting and disconnecting said teaser field resistor.

10. A control system as in claim 9 wherein said time delay means comprises amplifier means having an input terminal and an output terminal, a first capacitor connected between the input terminal and the output terminal, a first input resistor providing a time delay of a first predetermined duration, a second input resistor providing a time delay of a second predetermined duration, and rectifier means applying voltage of said one polarity from said comparison means to the first input resistor and applying voltage of said other polarity from said comparison means to the second input resistor.

11. A control system as in clAim 10 wherein said time delay means includes switching means connected to the output terminal of said amplifier means for conducting current when a voltage of said one polarity is applied to said time delay means and blocking current when a voltage of said other polarity is applied to said time delay means, said switching means being connected to a source of voltage of said other polarity, a second capacitor connected between the source of voltage and the input terminal of said amplifier means for discharging through said amplifier means when said switching means begins to conduct.

12. A control system as in claim 9 wherein said biasing means includes means connected between said relay means and said comparison means providing a first predetermined magnitude of said biasing signal and when said teaser field resistor is connected across said armature and a second predetermined magnitude of said biasing signal when said teaser field resistor is disconnected.

13. A control system as in claim 9 wherein said reference control means includes amplifier means having an input terminal, a first input resistor connected to the amplifier input terminal for receiving voltage of said selected polarity from said signal means, a second input resistor connected between the amplifier input terminal and a source of voltage of said selected polarity, and voltage divider means connected between the first and second input resistors and having a wiper connected at a voltage of predetermined magnitude.

14. A control system for operating a direct current motor comprising an armature and a series-wound field from an alternating current source, said system comprising a motor having an armature and a field, first and second AC-DC converter means each having control and power input terminals and output terminals, said source being electrically connected to the power input terminals of the first and second converter means, master switch means having an operating range for controlling operation of the motor when the motor is subject to an overhauling load, signal means for producing a voltage of a first polarity and of a magnitude controlled by said master switch means, reference control means electrically connected to said signal means and to the control input terminals of both the first and second converter means and responsive to the magnitude of the voltage from the signal means to control direct current output from both the first and second converter means, means connecting the armature across the output terminals of the first converter means and connecting the field across the output terminals of the second converter means, a dynamic braking resistor connected across the armature, and current sensitive means for disconnecting the dynamic braking resistor at a predetermined magnitude of direct current output from both the first and second converter means.

15. A control system as in claim 14 wherein said current sensitive means comprises current-indicating means for producing a current-magnitude signal indicating the magnitude of the direct current output from both said first and second AC-DC converter means, and load sensing means connected to said current-indicating means and responsive to said current-magnitude signal produced at said predetermined magnitude of direct current output to disconnect said dynamic braking resistor.

16. A control system as in claim 15 wherein said load sensing means comprises comparison means connected to said current-indicating means comparing said current-magnitude signal to a biasing signal of predetermined magnitude and producing a voltage of one polarity if said current-magnitude signal is greater than the biasing signal and of an other polarity if said current-magnitude signal is less than the biasing signal, time delay means connected to said comparison means and providing an output after a time delay, and relay means responsive to the output of the time delay means for disconnecting said dynamic braking resistor.

17. A control system as in Claim 16 wherein said time delay means comprises amplifier means having an input terminal, a first input resistor providing a time delay of a first predetermined duration, a second input resistor providing a time delay of a second predetermined duration, and rectifier means applying voltage of said one polarity from said comparison means to the first input resistor and applying voltage of said other polarity from said comparison means to the second input resistor.

18. A control system as in claim 14 wherein said reference control means includes matching means preventing material change in speed of said motor when said dynamic braking resistor is disconnected.

19. A control system as in claim 18 wherein said reference control means includes first amplifier means having an output terminal connected to said first AC-DC converter means and an input terminal, second amplifier means having an output terminal from which an output voltage is transmitted to the first amplifier means in response to an input voltage from said signal means, and third amplifier means having an output terminal and from which an output voltage is transmitted to the first amplifier means in response to an input voltage from said signal means, and said matching means includes switching means limiting the output voltage of the second amplifier means when said dynamic braking resistor is connected across said armature and limiting the output voltage of the third amplifier means when the dynamic braking resistor is disconnected, and means connected between the input terminal of the first amplifier means and the output terminals of the second and third amplifier means permitting the output voltage of greater magnitude to be applied to the first amplifier means.

20. A control system as in claim 19 wherein said reference control means includes fourth amplifier means having an output terminal connected to the control input terminal of said second AC-DC converter means and inverting a non-inverting input terminals, the inverting input terminal being connected to receive said voltage of said first polarity from said signal means, a source of voltage of a second polarity, opposite from said first polarity, connected to the inverting input terminal of the fourth amplifier means, and resistance means providing a portion of said signal means voltage to the non-inverting input terminal of the fourth amplifier means, and wherein said switching means includes means diverting said signal means voltage from the non-inverting input terminal when said dynamic braking resistor is connected across said armature.

21. A control system as in claim 20 including an additional current-indicating means serially connected with the output terminal of said second AC-DC converter means and wherein said reference control means includes means connected between said additional current-indicating means and the non-inverting input terminal of said fourth amplifier means for applying a voltage of said first polarity indicating the magnitude of direct current output of said second converter means to the non-inverting terminal.