Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
  • H02P7/06—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
  • H02P7/18—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power
  • H02P7/24—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices
  • H02P7/28—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices
  • H02P7/285—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only
  • H02P7/2855—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value

Definitions

• This invention relates to a device designed to provide automatic control of a DC motor speed or torque.
• the magnetic field is generally obtained by means of either a magnet or two or more windings, while the armature usually consists of three to five field poles in which the direct current flowing through the windings is switched by a commutator comprising two stationary brushes that slide on a rotating segmented commutator to automatically control the switching sequence.
• DC motors of this type are known to have several drawbacks, the main one being that temporary switching shorts occur on the segmented commutator and on brushes while the motor is running, and these shorts reduce the motor life in addition to generating switching noise.
• One such control is based on a switch operated by centrifugal force to open as soon as a preset speed is exceeded and close as soon as speed drops below that value.
• This type control constantly switches from one state to the other and generates switching noise as well as random stresses and vibrations during operation which may prove detrimental in certain applications.
• the main object of this invention is, therefore, to provide a device for automatic control of a DC motor whereby no commutator switching is used though operating a switched rotating armature motor in order to obtain unaltered power output without increasing the motor size.
• Another object of this invention is to provide a highly accurate most reliable control device able to operate under heavy operating conditions.
• One more object of this invention is to provide a multipurpose control device, easy to operate to obtain different control modes.
• One further object of this invention is to provide a control device of simplified and low-cost construction suitable for mass production.
• the DC motor automatic control device is characterized in that one armature current control unit is mechanically attached to the motor rotor so as to rotate along with it and receives positive and negative DC supply voltage through two continuous slip rings cooperating with two brushes which are in turn connected to the DC power source, while appropriate information transmission media outside the motor provide the control unit with the information required to accomplish armature current control.
• An additional advantage is the ability to change the motor operating parameters, as required, through the action of information transmission media, and extend this ability to the point of providing step-by-step mode of operation.
• closed loop control can be provided in the motor by simply comparing within the control unit the motor output parameters, e.g. position and speed, with the externally provided information.
• figure 1 is a schematic perspective view showing the position of the control device according to this invention
• figure 2 is a bloch diagram of the control device circuitry according to this invention
• figure 3 is a circuit diagram of one embodiment of the power circuit
• figure 4 is a time-phase diagram of the rotor winding supply currents
• figure 5 is a circuit diagram of a second embodiment of the power circuit.
• the present preferred embodiment of the automatic DC motor control device is comprised of a control unit 10, which is mechanically attached to the motor rotor to rotate along with it and is connected to windings 12, 14, 16 which produce magnetic fields on the rotor field poles.
• Control unit 10 receives positive and negative DC supply voltage through two slip rings 18 and 20 and two brushes 22 and 24 which are in turn connected to the DC power source that supplies the power required for operation of the motor.
• control unit 10 includes a decoding circuit 56 that detects the desired speed information, the present rotation revolutions per minute information, and the desired rotation timing and direction information.
• the desired speed information is sent, through lead 58, to oscillator circuit 60 whose frequency is present on lead 62 and can be varied according to the information conveyed by the desired speed signal in the form of one voltage value.
• This error signal is processed in a speed control circuit 70 and converted into a supply voltage error which is sent, through a lead 72, to a power circuit 74 which also receives the phase timing signals supplied by decoding circuit 56 through leads 76, 78, 80, 82, 84, and 86.
• Power circuit 74 supplies in turn the three windings 12, 14, and 16. Referring to figure 3, power circuit 74 includes six power transistors 88, 90, 92, 94, 96, and 98 which are connected and driven in such a way that the corrected voltage current supplied by control circuit 70 will alternately flow through windings 12, 14, and 16, as better shown in figure 4, the current flow time and direction being according to the desired rotation timing and direction information.
• the time axis is subdivided into 60-degree fractions of the motor rotation period and the ordinates show the phase relationship between current flows through windings 12, 14, and 16, respectively.
• a desired speed and desired rotation speed voltage is set in control signal generator 54 and applied to brush 52.
• the voltage on brush 52 is applied to the lead, out of the six 26, 28, 30, 32, 34,and 36, which comes into contact with brush 52 through the six-segment commutator 50.
• decoding circuit 56 will receive the following information while the motor is running: the desired speed information in the form of a voltage on the live lead, the desired rotation direction information in the form of a voltage polarity on the live lead, and the present rotor position information in the form of switching pulses between leads 26, 28, 30, 32, 34, and 36.
• the control voltage amplitude generates a signal on lead 58 and the switching frequency generates a speed signal on lead 64.
• the detected switching times together with the desired rotation direction data is used by decoding circuit 56 to generate saturation and cutoff signals for transistors 88, 90, 92, 94, 96, and 98, and the speed error signal present on lead 68 is used to cause a change in power circuit 74 supply voltage and hence a change in motor speed i.e. acceleration or deceleration.
• Switching of the control signal supplied by generator 54 does not cause any switching noise since no significant power is involved in the transmission of information contained in the control signal.
• the information conveyed by the control signal genera ted by generator 54 may be affected by parameters other than its amplitude: for instance the information may be conveyed by a square wave signal and may be affected by its mark-to-space ratio or its frequency.
• the present rotation rate information and the rotor winding power supply timing information can be generated by Hall effect sensors incorporated in the rotor and sequentially operated by either the motor stationary magnetic field or magnets placed on the stator. In that casen the desired speed and rotation direction information can be introduced by superimposing it to the supply voltage through brushes 22, 24.
• the desired speed and rotation direction can be generated locally at the control unit 10 input instead of being supplied by external sources.
• the only external information required will be the present rotation rate and timing which would be transmitted through the Hall effect sensors, as mentioned previously.
• a motor including a device according to this invention can be easily operated in the step-by-step mode: the only provision needed would consist in having the motor stopped upon the occurrence of an appropriately selected value of one of the information parameters that control the armature currents.
• the stop signal as decoded in control unit 10, would cause the supply voltage to be applied to one or more coils forming one phase of the armature winding, thus immediately stojj ping the motor.
• the step-by-step mode of operation would thus be obtained by sequentially supplying the windings.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)
• Control Of Multiple Motors (AREA)
• Connection Of Motors, Electrical Generators, Mechanical Devices, And The Like (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Cites Families (2)

• 1985
  • 1985-10-11 IT IT48662/85A patent/IT1182912B/it active
• 1986
  • 1986-10-11 WO PCT/IT1986/000073 patent/WO1987002527A2/en unknown
  • 1986-10-11 EP EP86906425A patent/EP0241531A1/en active Pending

Non-Patent Citations (1)

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