Speed control device for single phase motors

Claim 2

A speed control device for controlling the speed of a universal motor comprising a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element.

Claim 3

A speed control device according to claim 1, wherein said second circuit means comprises switch means selectively changeable between a first position where said series circuit is connected directly between said both terminals of said AC power source and a second position where said series circuit is connected through said motor between said both terminals.

Claim 4

A speed control device according to claim 1, further comprising a temperature-sensitive resistance means thermally coupled to said thyristor and connected in parallel with said capacitor.

Claim 5

A speed control device according to claim 1, wherein said movable shutter of said variable resistance means is urged in one direction of the movement of the same by a spring means.

Claim 6

A speed control device according to claim 3, wherein said thyristor and said trigger signal generator means are accommodated in a casing provided with a cover pivoted to said casing, the movement of said movable shutter being interlocked to the pivotal motion of said cover.

Claim 7

A speed control unit to be used for controlling the speed of a universal motor comprising a speed control device which comprises a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element; a casing having an open space for mounting therein said control device, a cover mounted on said casing so as to enclose said open space and to be pivotally movable in a pedal action, spring means for biasing said cover in one direction of said pedal action, means for movably mounting said movable shutter in said casing, and means for mechanically transmitting the movement of said cover to said movable shutter thereby causing said movable shutter to move with said pedal action.

Claim 8

A speed control unit to be used for controlling the speed of a universal motor comprising a speed control device which comprises a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element; a casing having an open space for mounting therein said control device, a cover mounted on said casing so as to enclose said open space and to be pivotally movable in a pedal action, spring means for biasing said cover in one direction of said pedal action, means for movably mounting said movable shutter in said casing, and means for mechanically transmitting the movement of said cover to said movable shutter thereby causing said movable shutter to move with said pedal action.