Mechanical optical comparators are precise measuring instruments used extensively in industries for dimensional inspection and quality control. Mechanical Comparators are devices which rely on optical principles to magnify and project the image of a workpiece onto a screen, enabling operators to compare it with a reference or master component visually. The mechanical design of these comparators includes a sturdy stage for positioning the workpiece, adjustable lenses or mirrors for varying levels of magnification, and a profile projector screen for clear and accurate visualisation.

The article discusses the Mechanical Optical Comparator, including its working principle, applications, Advantages, and disadvantages. This topic is important for your upcoming examinations like SSC JE ME and RRB JE Mechanical Engineering.

What are Mechanical Optical Comparator?

A mechanical comparator is a measuring instrument that utilises mechanical components such as gears, levers, pinions, and racks to achieve magnification, thereby enhancing measurement precision. The diagram of a mechanical comparator is depicted below.

Working Principle of Mechanical Optical Comparator

The working principle of a mechanical comparator revolves around utilising mechanical mechanisms to amplify minute deviations. In all mechanical comparators, a gear train lever system is employed to magnify the small movement of the indicator. These comparators offer magnifications ranging from 300 to 1000, making them highly effective for precise measurements. Commonly referred to as "microcators," mechanical comparators are particularly useful for linear measurements using the relative contact technique.

Also, learn about Bearings.

Mechanical comparators can be classified into various types, each serving specific measurement and comparison purposes:

Dial Indicators

Fig 1: Dial Indicators

Dial indicators are sensitive and versatile instruments that utilise a gear system with a pinion and rack for magnifying linear movements. They are employed to determine errors in geometrical forms such as roundness, taper, and parallelism, as well as for material compression and tension testing.

Reed-Type Comparators

Fig 2: Reed Type Comparator

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Reed-type comparators compare the dimensions of workpieces based on typical dimensions. Their internal construction and working principle are relatively simple, making them effective for measuring and displaying the difference in dimensions.

Johansson Mikrokator

Fig 3: Johansson Mikrokator

Johansson Mikrokator, invented by H. Abramson and manufactured by C.H. Johansson, is a mechanical comparator used for comparison and measurement. Its simple construction and working principle make it a significant tool for obtaining mechanical magnification.

Sigma Comparator

Sigma comparators are used for measuring the roughness of surfaces by comparing dimensional differences between standard and measured values. They employ a compression spring to limit measuring pressure, and the magnification achieved depends on the length of the lever on both sides of the pivot.

Fig 4: Sigma comparator

Mechanical vs Optical Comparators – Key Differences

Compartos are the precision measurement devices used in metrology. Mechanical Comparators are operated using levers, gears, and linkages to amplify small dimensional changes, offering sensitivity and accuracy. They are widely used in a workshop environment. On the other hand, optical comparators use mirrors and lenses to magnify measurements for high accuracy. Mechanical Comparators are cost-effective and portable while optical comparators are costly and require a power source. For more detailed information, candidates can refer to the table provided below. 

Mechanical Comparator vs Electrical Comparator

The difference between mechanical comparator and electrical comparator is discussed below. 

Advantages of Mechanical Optical Comparators

The advantages of mechanical comparators are as follows:

• Cost-Effectiveness: Mechanical comparators are more budget-friendly compared to other amplifying devices.
• No External Power Required: They do not rely on an external electricity supply, making them independent of power sources.
• High Magnification: Mechanical comparators offer extremely high magnification capabilities, ensuring accurate measurements.
• Lightweight Optical Lever: The optical lever used in these comparators is lightweight, facilitating precise measurements.
• Clear Linear Scale: Mechanical comparators feature a linear scale that is easy to understand and interpret.
• Compact and Robust: These comparators are compact, strong, and designed for simple operation, making them durable and reliable.
• Versatility in Workshop Conditions: Mechanical comparators are well-suited for normal workshop conditions and prove to be handy tools for various applications.

Disadvantages of Mechanical Optical Comparators

The disadvantages of mechanical comparators are as follows:

• Reduced Accuracy and High Friction: Mechanical comparators have more moving parts, leading to lower accuracy and increased friction, affecting their precision.
• Sensitivity to Negligence: Accuracy can be compromised if there is negligence or wear within the moving parts of the comparator.
• Vulnerability to Vibrations: The comparator's higher inertia makes it susceptible to vibrations, impacting its responsiveness.
• Limited Measuring Range: The measuring instrument's range is limited once the pointer moves above a fixed scale, restricting its measurement capabilities.
• High Parallax Error: Mechanical comparators are prone to a high parallax error, as the pointer moves on a fixed scale, affecting measurement accuracy.
• Difficulty in Magnification Adjustment: Integrating arrangements for adjusting magnification in mechanical comparators can be extremely challenging due to their complex design.

Also, get to know about Riveted Joints.

Applications of Mechanical Optical Comparator

Mechanical comparators find various applications in different industries due to their versatility and precision:

• Mass Production and Laboratory Testing: Employed for analysis purposes in mass production and laboratory testing.
• Manufacturing Companies: Widely used in manufacturing companies for measuring outer rings, bearing inner, bearing cages race, and cylindrical components in the automobile industry.
• Measurement Devices: Utilised in micrometres, small spring measuring heads, lever indicators, and spring-optical measuring heads for precise measurements.
• Surface Roughness Measurement: Useful for measuring surface roughness by comparing standard and measured values of surface materials.

This article threw light on Mechanical Optical Comparators and all the aspects related to it. We recommend our readers they should appear in the SSC JE Mechanical mock tests and SSC JE ME Previous Years Papers. Also, get enrolled in the AE/JE Mechanical coaching to get a firm grip on the subject.

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