1. Field of the Invention
This invention relates to a magnetic metal sensor for detecting a magnetic metal piece and a method for detecting magnetic metal using the magnetic metal sensor. As an example, the present invention relates to a magnetic metal sensor for detecting the possible presence of a magnetic metal piece or its displacement, a magnetic metal sensor for detecting a plurality of magnetic metal pieces from a unit under detection comprised of the magnetic metal pieces arranged side-by-side at a pre-set separation from one another.
2. Related Art
There has hitherto been known an eddy-current type sensor as a magnetic metal sensor for detecting the possible presence or displacement of magnetic metal.
This type of the magnetic metal sensor is desired to be used in a system, such as a machine tool for detecting the number of teeth of a gear for controlling the rpm of the rotational angle of the gear, or in a system for detecting the number of teeth used for knitting fibers in a knitting machine for cloths or chemical fibers for controlling the movement positions of the knitting bar of a comb-shaped knitting bar.
The magnetic metal sensor is also desired to be used in a system for judging whether or not a robot arm, for example, has approached a pre-set position to control the arm position, or in a system for detecting the slack or failure in tightening of a screw mounted on a work in order to check the operating process.
Meanwhile, the magnetic metal sensor of the eddy-current system is usually low in response rate. Thus, with the magnetic metal sensor of the eddy-current sensor, it has been difficult to detect a metal piece moved at an elevated speed or plural metal pieces paced side-b-side.
Also, the magnetic metal sensor of the eddy-current system is suddenly lowered in output level if the metal piece being detected is smaller in size than the coil making up the sensor. Thus, with the magnetic metal sensor of the eddy current system, it has been difficult to detect metal pieces of small sizes.
In addition, with the eddy-current type magnetic metal sensor, since the eddy current needs to flow through the metal piece by magnetic induction, the magnetic field applied from the coil to the metal piece needs to be sufficiently large to render it difficult to provide a sufficient distance between the coil and the metal piece.
By the above reason, it has been difficult to apply the eddy-current type magnetic metal sensor to a system for controlling the system for a machine tool or a system for controlling the destination of movement.