Control device for controlling the rotational speed of a portable power tool

In a portable electric tool having an electric motor for driving an adjustable tool holder capable of receiving and accommodating various size tools, the improvement comprising:

• sensor means operatively connected to said tool holder for sensing the size of the tool secured in said tool holder;
• speed control means operatively connected to said sensor means for controlling the speed of said motor in accordance with the sensed size of said tool;
• and
• wherein said tool holder comprises a chuck rotatably mounted to a shaft drivingly coupled to said motor, and said sensor means includes a sensor rod slidably disposed within a bore formed in said shaft.

In a portable electric tool having an electric motor for driving an adjustable tool holder capable of receiving and accommodating various diameter tools, the improvement comprising:

• sensor means operatively connected to said tool holder for sensing the diameter of the tool secured in said tool holder;
• potentiometer means connected to said sensor means for producing an output signal whose magnitude varies in accordance with the sensed diameter of the tool secured in said tool holder;
• control circuit means connected to said potentiometer means for varying the supply of current to said motor in accordance with the magnitude of said output signal;
• and
• switch circuit means connected between a source of electrical power and said potentiometer means for controlling the magnitude of the signal supplied to said potentiometer means.

A portable electric tool comprising:

• a housing;
• a motor mounted in the housing;
• a control circuit for controlling the speed of the motor;
• a tool holder adjustable for accommodating a tool therein of any diameter selected from a plurality of tools having respectively different diameters;
• the control circuit including a control member for adjusting the speed of the motor;
• and,
• sensor means operatively connecting the tool holder to the control member in response to the diameter of the tool inserted into the tool holder thereby automatically adjusting the speed of the motor in response to the diameter of the tool.

A portable electric tool comprising:

• a housing;
• a motor mounted in the housing;
• a control circuit for controlling the speed of the motor;
• a tool holder adjustable for accommodating a tool therein of any size selected from a plurality of tools having respectively different sizes;
• the control circuit including a control member for adjusting the speed of the motor;
• sensor means operatively connecting the tool holder to the control member in response to the size of the tool inserted into the tool holder thereby automatically adjusting the speed of the motor in response to the size of the tool;
• the tool holder having a thrust plate movable for and aft to a position dependent upon the size of the tool inserted into the tool holder;
• the sensor means including a rod-like structure slideably mounted in the housing and, resilient means resiliently biasing one end of said rod-like structure against the thrust plate;
• and,
• said control member being a potentiometer connected into said control circuit and having a wiper arm connected to the other end of said rod-like structure.

An electric tool comprising:

• a housing;
• a motor mounted in the housing;
• a control circuit for controlling the speed of the motor;
• a tool holder adjustable for accommodating a tool therein of any diameter selected from a plurality of tools having respectively different diameters;
• the control circuit including a control member for adjusting the speed of the motor;
• and,
• sensor means operatively connecting the tool holder to the control member in response to the diameter of the tool inserted into the tool holder thereby automatically adjusting the speed of the motor in response to the diameter of the tool.