Motor speed sensing system for magnetic disk apparatus or the like

A system for sensing the traveling speed of an object driven by an electric motor of the kind having a drive coil to be energized by a driver circuit under the control of a motor speed control signal supplied by motor speed control means, the system comprising:

• (a) a speed sensor comprising a speed sensing coil for electromagnetically generating a voltage proportional to the traveling speed of the object, the speed sensing coil being disposed in the vicinity of and magnetically coupled to the drive coil of the motor so that the voltage generated by the speed sensing coil includes a noise component induced by the flow of an electric current through the drive coil;
• (b) a noise suppression signal generator circuit connected to the motor speed control means for deriving from the motor speed control signal a noise suppression signal equivalent to the noise component of the output voltage of the speed sensing coil;
• and
• (c) a noise suppressor circuit connected to both the speed sensing coil and the noise suppression signal generator circuit for eliminating the noise component from the output voltage of the speed sensing coil by the noise suppression signal.

A system for sensing the traveling speed of an object driven by an electric motor of the kind having a drive coil disposed in the vicinity of magnetic field generating means, the drive coil being energized by a driver circuit under the control of a motor speed control signal supplied by motor speed control means, the system comprising:

• (a) a speed sensing coil mounted to the motor driven object for joint movement therewith and disposed in the vicinity of and magnetically coupled to the field generating means of the motor for electromagnetically generating a voltage proportional to the traveling speed of the object, the speed sensing means being also to be disposed in the vicinity of the drive coil of the motor so that the voltage generated by the speed sensing coil includes a noise component induced by the flow of an electric current through the drive coil;
• (b) a noise suppression signal generator circuit to be connected to the motor speed control means for deriving from the motor speed control signal a noise suppression signal equivalent to the noise component of the output voltage of the speed sensing coil;
• and
• (c) a noise suppressor circuit connected to both the speed sensing coil and the noise suppression signal generator circuit for eliminating the noise component from the output voltage of the speed sensing coil by the noise suppression signal.

In an apparatus having a transducer mounted to a pivoted support beam for data transfer with a rotating disklike record medium having a multiplicity of annular data storage tracks arranged concentrically thereon, and a seek motor of the kind having a drive coil for driving the support beam in order to move the transducer from track to track on the record medium, a system for controlling the traveling speed of the transducer across the tracks on the record medium, comprising:

• (a) motor speed control means for providing a motor speed control signal representative of a desired traveling speed of the transducer;
• (b) a speed sensor comprising a speed sensing coil for electromagnetically generating a motor speed signal representative of the actual traveling speed of the transducer, the speed sensing coil being to be disposed in the vicinity of the drive coil of the seek motor so that the motor speed signal includes a noise component induced by the flow of an electric current through the drive coil;
• (c) a differentiator circuit for providing a noise suppression signal equivalent to the noise component of the motor speed signal;
• (d) first differential amplifier having a first input connected to the speed sensor and a second input connected to the differentiator circuit for removing the noise component from the motor speed signal by the noise suppression signal;
• (e) a second differential amplifier having a first input connected to the motor speed control means and a second input connected to the first differential amplifier for providing an output corresponding to the difference between the motor speed control signal and the noise-free motor speed signal;
• and
• (f) a driver circuit connected between the second differential amplifier and the seek motor for driving the latter as dictated by the output from the former;
• (g) the differentiator circuit being connected to the second differential amplifier for deriving the noise suppression signal from the output therefrom.