Precision Measurement: Comparators and Talysurf Technology

The Optical System in a Mechanical-Optical Comparator

In a mechanical-optical comparator, the optical system is crucial for magnifying small displacements of a plunger or measuring contact. It projects the result onto a screen, allowing for easy and precise reading. The system generally includes several key components:

• A light source
• A mirror or prism
• A pivoted lever system
• A lens system
• A graduated scale or screen

How the Optical Comparator Works

When the plunger makes contact with the workpiece, any small displacement resulting from dimensional variation is transferred through a mechanical linkage (such as a lever). This movement causes a mirror or prism attached to the linkage to tilt. A beam of light is reflected by the mirror through the lens system, projecting a magnified image or scale movement onto a screen. Even a tiny movement of the plunger can result in significant movement of the projected image, thus providing high sensitivity and magnification.

Advantages of Optical Comparators Over Mechanical Types

1. High Magnification: Optical comparators offer significantly higher magnification (up to 50x or more), allowing for the detection of very small dimensional changes.
2. Reduced Friction Errors: Since there is minimal mechanical contact in the optical path, friction and wear are substantially reduced, improving overall accuracy and durability.
3. Less Mechanical Inertia: Optical components are lighter and respond faster than fully mechanical systems, enhancing responsiveness and precision in measurement.
4. Improved Accuracy and Readability: The projected display is easier to read, which reduces operator error and improves measurement consistency.
5. Elimination of Backlash Issues: While mechanical comparators may suffer from backlash due to gears and levers, optical comparators eliminate this issue entirely through light-based movement indication.

Taylor-Hobson Talysurf: Surface Texture Measurement

The Taylor-Hobson Talysurf is an advanced instrument used for precise surface texture measurement. It evaluates critical parameters such as surface roughness, waviness, and form errors with high accuracy.

Talysurf Construction Components

1. Stylus and Skid Assembly:
   • The main sensing element is a diamond-tipped stylus mounted on a lever system.
   • A skid (reference surface) travels along the surface with the stylus, helping to maintain a consistent reference level.
2. Transducer (Pickup Unit):
   • The stylus is connected to an electromechanical transducer, typically an inductive or Linear Variable Differential Transformer (LVDT) type.
   • As the stylus moves over surface irregularities, this vertical motion is converted into proportional electrical signals.
3. Traversing Unit:
   • The stylus and skid are mounted on a motorized traversing unit, which moves horizontally across the surface at a constant, controlled speed.
4. Amplifier and Data Acquisition System:
   • The electrical signals generated by the transducer are amplified and sent to a dedicated data processing unit.
5. Display or Computer Interface:
   • The processed data is displayed as a profile graph or numerical values representing standard surface roughness parameters (e.g., Ra, Rz) on a screen or printed output.

Principle of Operation (Working)

• The stylus is carefully placed on the workpiece surface, and the traversing unit begins moving it in a straight line across the area to be measured.
• As the stylus encounters microscopic peaks and valleys, it moves vertically.
• This vertical movement is instantly converted into proportional electrical signals by the transducer.
• The signals are then amplified, filtered, and sent to the processing unit, where they are converted into a 2D surface profile representation.
• Finally, the required roughness parameters are calculated and displayed for detailed interpretation and quality control.