What Is a Linear Gauge?
A linear gauge is a measurement device that determines the displacement of an object. It utilizes optical methods to measure displacement, involving a moving slit attached to the object, two fixed slits, and a machine that converts the slit waveform into a pulse wave. The displacement is interpreted from the number of wave pulses, with accuracy dependent on slit spacing.
Applications of Linear Gauge
Linear gauges are primarily used in machine tool control across various industries, including automotive, home appliances, machinery parts, logistics, and research. Selecting the right gauge involves considering its accuracy, environmental suitability, and mountability.
1. Machine Tools
In machine tools, such as lathe equipment and milling machines, linear gauges measure shaft rotation speeds and the travel of cutters and drills.
2. Load Displacement Measurement
They are used to measure displacement under a constant load, such as in testing the strength of automobile bodies or doors.
Principle of Linear Gauge
Linear gauges function by detecting changes in light patterns caused by the movement of the object.
1. Calculation of Displacement
Displacement is calculated based on the light passing through the moving slit and its variation in relation to the fixed slits.
2. Orientation Calculation
The gauge calculates the direction of movement by observing the phase shifts in the light pattern between the moving and fixed slits, outputting two square wave signals with a 90° phase difference.
Structure of Linear Gauge
A linear gauge comprises a detection part with a light source and slits and a counting section that transforms light waveforms into pulse waves.
1. Detection Part
The detection part includes a light source, two fixed slits, and a moving slit attached to the measured object. The fixed slits are offset to discern the movement direction of the moving slit. The output signal is either 4um or 40um per pitch, depending on the resolution type.
2. Counting Section
The counting section, consisting of a light-receiving element and a counter, multiplies the signal to achieve a measurement resolution of a quarter pitch.
Other Information on Linear Gauge
1. Indication Accuracy
Indication accuracy refers to the measurement error of the linear gauge, calculated over the entire length of the moving slit’s travel.
2. Temperature Effect
Accuracy is affected by temperature. The linear expansion coefficient of the glass scale used in the detection section is considered to calculate indication accuracy at different temperatures.