Bridge Structure for Coordinate Measuring Machines

Product Specifications

Technical details and manufacturing context for Bridge Structure

Definition

In a Precision Industrial Coordinate Measuring Machine (CMM), the Bridge Structure is the critical load-bearing framework that spans the measurement volume. It provides the rigid foundation for the X-axis rail system and supports the Y-axis carriage and Z-axis probe assembly, ensuring dimensional stability and accuracy during measurement operations. The bridge structure moves along the X-axis rails on the machine base. Its primary function is to provide a stable, rigid platform that minimizes deflection and vibration, thereby maintaining the precise geometric relationship between the probe and the workpiece being measured. Its movement, combined with the Y-axis carriage and Z-axis ram, allows the probe to access any point within the machine's volumetric envelope. The bridge is typically constructed from materials such as granite, aluminum alloy, cast iron, or carbon fiber reinforced polymer, each offering different trade-offs in stiffness, weight, and thermal stability. The selection of bridge material and design directly influences the machine's maximum permissible error (MPE_E), resolution, and dynamic performance. For instance, granite provides superior thermal stability and damping, while aluminum alloy offers lower weight for higher acceleration. The bridge structure must be designed to minimize deflection under load and thermal gradients, as these can introduce measurement errors. The guide system, often air bearings or linear guides, ensures smooth and precise motion along the X-axis. The bridge's mass and stiffness contribute to the overall machine weight, which ranges from 500 to 5000 kg, affecting stability and vibration isolation. The operating environment, including temperature and humidity, must be controlled within specified ranges to maintain accuracy. The bridge structure is a fundamental component that determines the CMM's measuring range, which can vary from 500×400×300 mm to 3000×2000×1500 mm. It is essential to verify model-specific values and standards with the legal manufacturer or supplier.

Working Principle

The bridge structure moves along the X-axis rails on the machine base. Its primary function is to provide a stable, rigid platform that minimizes deflection and vibration, thereby maintaining the precise geometric relationship between the probe and the workpiece being measured. Its movement, combined with the Y-axis carriage and Z-axis ram, allows the probe to access any point within the machine's volumetric envelope. The bridge is typically driven by motors and guided by air bearings or linear guides, ensuring smooth and precise motion. The rigidity of the bridge is crucial to prevent bending or twisting that could cause measurement errors. The bridge's design must account for thermal expansion and dynamic forces during acceleration and deceleration. By maintaining a stable platform, the bridge ensures that the probe's position is accurately known relative to the workpiece, enabling precise dimensional measurements.

Common Materials

Granite, Aluminum Alloy, Cast Iron, Carbon Fiber Reinforced Polymer

Technical Parameters

Parameter	Typical range	Notes & selection driver
Measuring Range (X×Y×Z)	500×400×300–3000×2000×1500 mm	Select based on workpiece size; larger range reduces accuracy.
Maximum Permissible Error (MPE_E)	1.5–15 µm	Tighter tolerance for high-precision applications.ISO 10360-2
Resolution	0.1–1 µm	Higher resolution improves fine feature detection.
Maximum Drive Speed	200–500 mm/s	Higher speed increases throughput but may affect accuracy.
Maximum Acceleration	500–2000 mm/s²	Higher acceleration reduces cycle time.
Operating Temperature Range	15–30 °C	Temperature stability critical for accuracy.ISO 10360-2
Temperature Gradient	1–3 °C/h	Exceeding gradient may cause thermal drift.
Relative Humidity Range	40–60 % RH	Condensation can damage scales and electronics.
Air Supply Pressure	0.4–0.6 MPa	Required for air bearings; low pressure causes friction.ISO 8573-1
Air Consumption	50–200 L/min	Higher consumption increases operating cost.
Bridge Material	Aluminum–Granite	Granite provides better thermal stability.
Guide System	Air–Linear	Air bearings offer frictionless motion.
Machine Weight	500–5000 kg	Heavier machines provide better stability.

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM

X-Axis Guide Rails Part
Provide a precision linear bearing surface for the bridge's movement along the machine base.

Material: Hardened Steel or Ceramic
Bridge Beam
The primary horizontal member that spans the measurement table, providing structural rigidity.

Material: Granite, Aluminum Alloy, or Cast Iron
Drive System Mounting Points Part
Interface for the motor, gearbox, and feedback system (e.g., linear encoder) that controls bridge movement.

Material: Steel or Aluminum Alloy
Y-Axis Carriage Mounting Interface Part
The surface or rail on which the Y-axis carriage is mounted and moves perpendicular to the bridge travel.

Material: Hardened Steel or Granite

Manufacturers of Bridge Structure

2 companies list this product among what they make. Company figures are quoted from each company's own website; every card states where the relationship came from.

BETTERCOVER

Wenzhou, Zhejiang, CN

Also makes: Manhole Cover

Listed on the company's own website · profile compiled by CNFX from public sources

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ESC Steel Structures

Shanghai, CN

Also makes: Pressure Vessel, Bridge Girder

Listed on the company's own website · profile compiled by CNFX from public sources

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Frequently Asked Questions

What is the function of the bridge structure in a CMM?

The bridge structure is the rigid framework that spans the measurement volume and supports the X-axis rail system, Y-axis carriage, and Z-axis probe assembly. It moves along the X-axis rails to position the probe, ensuring dimensional stability and accuracy during measurement.

What materials are commonly used for the bridge structure?

Common materials include granite, aluminum alloy, cast iron, and carbon fiber reinforced polymer. Each material offers different properties in terms of stiffness, weight, and thermal stability, affecting the machine's accuracy and dynamic performance.

How does the bridge structure affect measurement accuracy?

The bridge's rigidity minimizes deflection and vibration, maintaining the precise geometric relationship between the probe and workpiece. Thermal stability and damping characteristics also influence accuracy, as temperature changes can cause expansion or contraction.

What parameters should be verified when selecting a bridge structure?

Key parameters include measuring range, maximum permissible error (MPE_E), resolution, maximum drive speed, acceleration, operating temperature range, temperature gradient, relative humidity, air supply pressure, air consumption, bridge material, guide system, and machine weight. Always confirm these values with the manufacturer for your specific application.

Data Basis

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Preliminary Technical Classification

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pressure:	N/A (structural component, not pressure-bearing)
other spec:	Maximum permissible error (MPE): ±(1.5 + L/350) μm where L is measurement length in mm, Vibration tolerance: <0.5 m/s² RMS, Humidity: 40-60% RH
temperature:	+15°C to +30°C

Bridge Structure

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