1. Field of the Invention
This invention relates to a flatness measuring apparatus for measuring flatness of a surface of a plate-shaped object such as a magnetic disk to be used as storage medium for computers.
2. Related Art Statement
For example, magnetic disks to be used as storage medium for computers typically comprise a substrate made of aluminum alloy or glass and a magnetic film formed on the surface of the substrate.
For manufacturing high quality magnetic disks, the disks are required to show a certain level of surface flatness, so their substrates are normally checked for flatness of the surface in an after-fabrication process.
Electric micrometers are known as means for checking whether the object of examination such as a plate-shaped product shows a predetermined level of surface flatness. The electric micrometer is in fact a displacement sensor comprising a probe and a transducer for transducing any mechanical displacement of the probe into an electric signal such that, as the probe is driven to slidingly move on the surface of a plate-shaped object, any displacement of the probe on the surface is transferred to the core of the actuator transformer of the sensor and detected as electric signal representing the surface condition of the object.
However, with a method of measuring the surface flatness of an object by holding a contact probe in contact with the surface of the object, the contact probe may damage and leave one or more than one flaws on the surface. Such a flaw should be avoided by any means particularly when it comes to a magnetic disk that requires a mirror finish to say nothing of a highly smoothed surface. Additionally, for the purpose of measuring efficiency, the operation of observing the surfaces of products supplied on a mass production basis is preferably automated.