Printing apparatus

Claim 2

A printing apparatus which includes an image forming means for forming a toner image, a feeding means for feeding a medium, a transferring means for transferring the toner image from said latent image forming means to the medium fed by said feeding means at an intermediate position along a medium feed path, and a heat roller fixing unit in which a pressure roller and a heat roller are arranged in opposition to each other, and said medium is passed between said rollers to fix said image formed thereon, wherein said pressure roller is formed so as to be moveable upward and downward; and said heat roller fixing device comprises a heat roller unit in which said heat roller is supported, and a main fraim having guide rails for said heat roller unit, and said heat roller unit can be inserted in and withdrawn from said main frame along said guide rails when said pressure roller is moved downward.

Claim 3

A printing apparatus according to claim 1, wherein said heat roller fixing unit has a driving portion formed by a gear construction having chamfered gear portions; and said driving portion is engaged with a driving gear provided in said main frame when said heat roller unit is inserted in to said main frame, and an engaging member for fixing said heat roller fixing units inserted along said guide rails is mounted on said main frame.

Claim 4

A printing apparatus according to claim 1 or 2, wherein said compression roller is mounted on a frame on which standby rollers, feed rollers and a discharger are mounted, and said compression roller is moved upward and downward in accordance with the movement of said frame.

Claim 5

A printing apparatus according to claim 1, 2 or 3, wherein said compression roller is supported by a member having a poor thermal transmission coefficient on said frame.

Claim 6

A printing apparatus according to any preceding claim, wherein said heat roller fixing apparatus comprises a thermistor for detecting a variation of a resistance value thereof and supplying a power source to a heater in said heat roller and maintaining said heat roller at a predetermined temperature, said heat roller fixing apparatus comprises a connector which connects said thermistor and said main frame and which includes a first terminal for supplying a current to said thermistor via a first resistor in said main frame and a second terminal for supplying a current via a second resistor in said main frame and a common terminal, a detector circuit for detecting an electric potential at said first and said second terminals, the output of said first terminal controlling the temperature of said heat roller, and when said connector is disconnected, the supply of the power source is stopped by detecting the potential of said second terminal regardless of the potential of said first terminal.

Claim 7

A printing apparatus according to any preceding claim, wherein said first resistor is connected to a power source, and said first terminal and said common terminal are grounded.

Claim 8

A printing apparatus according to any preceding claim, wherein said power source is connected to said first terminal, and said common terminal is connected via said first resistor to ground.