Braking device for a small DC motor

• US 3,919,611 A
• Filed: 12/07/1973
• Issued: 11/11/1975
• Est. Priority Date: 12/11/1972
• Status: Expired due to Term

• Current Assignee: Kazuo Onishi, Tadashi Takahashi
• Original Assignee: Kazuo Onishi, Tadashi Takahashi
• Inventors: Takahashi, Tadashi, Onishi, Kazuo
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Duncanson, Jr., W. E.
• Application Number:
  US05/422,723
• Time in Patent Office: 704 Days
• Field of Search: 318/379,380
• US Class Current: 318/380
• CPC Class Codes: H02P 3/12 by short-circuit or resistive braking

Abstract

A small DC motor has its terminals connected to the collector and emitter of a transistor, respectively, to reduce the time required for stopping the revolution of the motor, and the transistor is rendered conductive by a counter electromotive force of the motor. The counter electromotive force generated by rotation of the motor due to inertia thereof upon interruption of a motor driving power supply causes the transistor to be made conductive and a short-circuit current to flow therethrough with the result of generation of a braking force.

Claims

1. A braking device for a D.C. motor comprising a D.C. power supply for said D.C. motor;

switching means for controlling said D.C. power supply, said switching means enabling said D.C. power supply to supply power to said D.C. motor when said switching means is in its closed position and disabling said D.C. power supply when said switching means is in its open positions;

a first transistor having an emitter, collector and base, said emitter being connected to one terminal of said D.C. motor and said collector being connected to the other terminal of said D.C. motor;

a first resistor connected between said base and said collector of said first transistor;

a second transistor having an emitter, collector and base, said collector of said second transistor being connected to said one terminal of said D.C. motor, and said emitter of said second transistor being connected to said base of said first transistor and to one terminal of said switching means, so that said first transistor is reverse biased when said switching means is in its said closed position and automatically acts to brake said D.C. motor when said switching means is in its said open position; and

speed detector means, responsive to the rotational speed of said D.C. motor, for supplying the base current of said second transistor in proportion to said rotational speed, whereby said power supplied to said D.C. motor is varied to keep said rotational speed constant when said switching means is in its said closed position.

2. a braking device as claimed in claim 1, wherein said the speed detecting the comprises an A.C generator mechanically coupled to the axis of said motor, rectifying means for rectifying an output from said generator and a smoothing capacitor for storing the rectified output, a voltage across said capacitor being adapted to cause the base current of said second transistor to be varied.

3. A braking device as claimed in claim 2, further including a third transistor having an emitter, collector and base, said collector of said third transistor being connected to said base of said second transistor, said emitter of said third transistor being coupled to said other terminal of said DC motor and to one terminal of said DC power supply, and said base of said third transistor being connected to a common terminal to which said smoothing capacitor and said rectifying means are both connected.

4. A braking device as claimed in claim 3, further including a second resistor connected between said emitter of said third transistor and said smoothing capacitor, and a third resistor connected between said common terminal and said base of said first transistor.

5. A braking device as claimed in claim 1, wherein said speed detector means comprises means for detecting a counter electromotive force of said motor including a bridge circuit having at one branch said motor and at three other branches separate resistors, and control means for varying the base current of said second transistor depending on said counter electromotive force.

6. A braking device as claimed in claim 5, further including a third transistor having an emitter, collector and base, said collector of third transistor being connected to said base of said second transistor, said base of said third transistor being connected to said base of said first resistor and said emitter of said third transistor being connected to rectifying means, said rectifying means being connected across respective terminals of two of said separate resistors.

7. A braking device as claimed in claim 1, wherein the base of said first transistor is provided with means for amplifying the base current thereof.

8. A braking device as claimed in claim 1, wherein the collector of said first transistor is connected to the terminal of the motor through resistor means.