What Is a Shape Measuring Machine?
Shape Measuring Machines are devices used to record, analyze, and measure the contour shape of an object by accurately tracing the shape of its surface.
Shape Measuring Machines can be divided into two main types. The contact type uses a stylus (stylus) and the non-contact type uses a laser or other means to trace the surface. Shape Measuring Machines of the non-contact type are relatively easy to use, but they can be greatly affected by the material and properties of the object’s surface. For this reason, contact Shape Measuring Machines are the most common type.
Shape Measuring Machines have high resolution and can trace contours to 0.001 mm or less. However, measurement beyond the movable range of the stylus is not possible, so careful consideration should be given when making measurements with large height directions.
Uses of Shape Measuring Machines
Shape Measuring Machines are used in the development, production, and quality control of industrial products, particularly metals. Shape Measuring Machines are used to measure and analyze the contour of an object, including dimensions, angles, steps, and thread pitch.
Shape Measuring Machines that are CNC-controllable can be programmed to perform a series of measurement operations and used for automatic measurement on the production line. For example, standardized shapes, such as the screw shape of a plastic bottle lid, are generally quality-controlled by Shape Measuring Machines. For products whose shape itself is patented, the contour shape is specified in detail.
Principle of Shape Measuring Machines
This section describes the principle of contact Shape Measuring Machines, which are the mainstream of Shape Measuring Machines. Shape Measuring Machines plot the contour shape of the object to be measured as the displacement of a stylus attached to a horizontally moving detector and the stylus moves up and down.
While moving the stylus, the contour shape is traced by continuously plotting the X coordinate of the horizontal movement and the Y coordinate of the vertical position of the stylus at a pitch of about 0.001 mm on a digital scale.
The vertical movement of the stylus on most Shape Measuring Machines is an arc movement around a center called a pivot. Therefore, the greater the vertical movement of the stylus from the horizontal position, the greater the horizontal error caused by the arc. The stylus tip position must be detected while constantly compensating for this error.
In addition, as the stylus tip is in continuous contact with the object being measured, the stylus wears. As the stylus wears, the position of the stylus tip changes by the amount of wear. It is necessary to periodically check the stylus tip shape and make corrections according to the amount of wear.
Other Information on Shape Measuring Machine
1. Difference Between Shape Measuring Machine and Contour Measuring Machine
Shape Measuring Machines and Contour Measuring Machines usually refer to the same thing. However, there are situations in which the names must be used with strictly separate meanings, such as the following:
The strict distinction between the two is based on whether the contour measurement is continuous or discontinuous. In other words, a Contour Measuring Machine is a continuous measurement where the stylus is in constant contact, while a Shape Measuring Machine includes non-continuous measurements. For example, a shape is represented by measuring the displacement over a certain distance at equally spaced intervals and connecting the measurement points.
Since displacement cannot be measured between measurement pitches, the pitch must be shortened or supplemented by obtaining an approximate equation from the coordinates of the measurement points. Therefore, the accuracy, such as tracing power and minimum resolution to accurately measure the shape, varies depending on the fineness of the measurement pitch.
2. Handy Type Shape Measuring Machine
A handheld Shape Measuring Machine is used when measuring objects that are too large to be measured with a stationary Shape Measuring Machine or when measuring simply at the line side.
When using a handheld Shape Measuring Machine to measure a large object, it is impossible to measure the entire shape. Use a handheld type form measuring machine only for limited measurement areas, such as areas where strict dimensional tolerances are required or where changes in form can significantly affect function, performance, or safety.
3. Situations in Which a Surface Texture Measuring Machine Is Used as a Shape Measuring Machine
The measuring principle of a surface roughness measuring instrument is a combination of the horizontal X-axis and the vertical displacement of the stylus in the Z-axis direction. This is the same measuring principle used in Shape Measuring Machines, so as long as the X-axis and Z-axis are within the measurable range, it is possible to use a Surface Roughness Measuring Machine as a Shape Measuring Machine.
However, since surface roughness evaluation requires higher precision than shape measurement, the stylus tip shape and the detector must also have higher resolution.