Magnetic Or Optical Ruler For Machine Tool Measurement ,how To Choose?

characteristic

Grating ruler

Magnetic scale

Core Principles

Optical Principles + Moire Fringe Interference

Principles of Magnetism + Magnetoresistance Effect

Core structure - scale body

Material

Glass or Steel Strip

Steel strip or metal rod

Determinants

Line density determines basic resolution

Pole pair density determines basic resolution

Core structure - reading head

Core Components

1. Light source
2. Collimating lens
3. Indicator grating
4. Photodetector
5. Signal processing circuit

1. Sensitive element
2. Signal processing circuit

characteristic

Grating ruler

Magnetic scale

Accuracy

Very high (up to ±1μm/m or even higher). Less affected by the thermal expansion coefficient of the material (especially glass), and the manufacturing process is mature.

High (typically ±5μm/m to ±10μm/m, high-end can reach ±3μm/m). The accuracy is slightly lower than the top grating scale. Magnetic signal stability and temperature influence are key.

Resolution

Very high (common at the nanometer level). Achieved through high-density line markings and fine electronic subdivision.

High (micrometer level is common, 0.1μm or higher is also possible). Achieved through high density of magnetic pole pairs and electronic subdivision.

Maximum measuring length

Theoretically, it is very long (tens of meters). Glass scales are fragile and need to be spliced for long travel, which affects the accuracy; steel tape grating scales are longer and more durable.

Long (tens of meters to hundreds of meters). The steel belt base material is flexible and easy to install, and the long stroke is seamless and continuous, with obvious advantages.

Response speed/maximum moving speed

Very high (up to 10m/s or even higher). Optical signal response is fast.

High (can reach several m/s, such as 5m/s). Usually can meet most high-speed application requirements.

Anti-pollution ability

Low. Dust, oil, cutting fluid, and condensed water can block the optical path, causing signal loss or errors. A well-sealed or clean environment is required.

Very high. Dust, oil, cutting fluid, non-magnetic debris, condensed water have little effect on it. Especially suitable for harsh industrial environments.

Vibration/shock resistance

Medium. Glass rulers are brittle and easily broken by severe impact. The gap between the reading head and the ruler is small, and large vibrations may cause collisions.

High. All-metal structure (ruler and reading head), strong and durable, more able to withstand shock and vibration. The reading head gap is usually larger and the tolerance is good.

Anti-electromagnetic interference

High. Optical signals are less susceptible to interference from electromagnetic fields.

Moderate. Magnetic signals may be interfered by strong magnetic fields (such as nearby large motors and transformers). Attention should be paid to installation location and shielding.

Temperature Effect

Low. Especially with scales made of materials with low thermal expansion coefficients. Differences in thermal expansion coefficients between glass and metal need to be compensated.

The thermal expansion coefficient of the magnetic scale (steel strip) is relatively large, and temperature changes directly affect the measurement accuracy, requiring effective temperature compensation technology.

Installation Requirements

The gap between the reading head and the grating ruler is very small and must be strictly parallel, so installation and debugging must be meticulous. Long rulers require precise support.

The gap between the reading head and the magnetic scale is large (millimeter level), the installation tolerance requirement is relatively loose, and it is easier to install and debug. The magnetic tape is flexible and easy to install.

Durability/Lifespan

Moderate. Glass scale is fragile and the scale lines may wear out. Steel tape scale is more robust. The scanning head may fail due to contamination.

High. All-metal construction, resistant to wear and corrosion (especially stainless steel tape). No physical wear of the markings. Usually longer service life.

cost

Higher. Especially for high-precision, high-resolution, and long-stroke products. The cost of glass scale is higher than that of magnetic scale.

Low. Material cost and manufacturing process are relatively simple. Long stroke cost advantage is significant.

Typical application environment

Laboratories, metrology rooms, precision machine tools (CNC machining centers, grinders), semiconductor equipment, clean environments.

CNC machine tools (lathes, milling machines, machining centers), woodworking machinery, automated production lines, handling equipment, hydraulic cylinders, injection molding machines, steel rolling equipment, harsh working conditions (oil, dust, vibration).

Selection criteria

Grating ruler

Magnetic scale

Accuracy requirements

Nanoscale (highest precision)

Micron level (high precision but not extreme)

Resolution requirements

Extremely high resolution (nanometer level)

High resolution (micrometer level, supporting 0.1μm)

Cleanliness

Clean, dry, oil-free environment

Harsh environment (oil, water vapor, dust, metal chips)

Vibration/shock resistance

Medium (glass ruler is fragile)

High (all metal impact resistance)

Anti-electromagnetic interference

Very high (optical signal interference resistance)

 Medium (need to avoid strong magnetic fields)

Installation complexity

High (needs precise clearance adjustment)

Low (high tolerance, mm clearance)

Budget requirements

Higher (especially high precision/long stroke)

High cost performance (significant cost advantage)

Temperature stability

Low (low expansion material optional)

Temperature compensation is required (the thermal expansion coefficient of the steel strip is large)

Extra long travel

Limited (glass ruler needs to be spliced)

Seamless and continuous (tens of meters to hundreds of meters)

Typical application scenarios

Coordinate measuring machines, laboratory instruments, photolithography machines

High-end CNC machine tools (grinders, machining centers)

Semiconductor equipment, clean environment

Construction machinery, hydraulic systems,

Ordinary CNC machine tools (lathes, milling machines)

Automated production lines, material handling equipment, steel rolling equipment