Terms and Concepts

A Mech-Metrics project is a project created by the user in Mech-Metrics to maintain and manage an inline measurement project. A Mech-Metrics project contains a complete set of measurement configurations, which enables the management of the entire measurement process from part import, reference frame establishment, and measurement item configuration to data collection and analysis.

A Mech-MSR solution refers to a Mech-MSR solution specifically configured for measuring a particular part. When you use Mech-Metrics, you need to associate a part with its Mech-MSR solution.

A part refers to an individual workpiece that is processed or assembled during production.

A fixture refers to equipment, grippers, or devices used to secure and position a part, ensuring its correct location and orientation during manufacturing or assembly.

Clamping refers to the use of fixtures to hold and position a part, ensuring its correct location and orientation during manufacturing or assembly.

A feature refers to specific geometric elements or attributes of a part, such as its shape, dimensions, and so on. The features that can be measured in this software include circle, slot, cylinder, point, line, plane, rectangle, pattern, distance, and angle.

The feature ID is an integer used to uniquely identify the feature in the software. The value range is 1 to 999.

The software supports three types of feature attributes for measurement:

A measurement item refers to an item that you can create in the current project, for which measurement values need to be obtained through measurement. It includes features (such as circles, slots, cylinders, points, lines, planes, rectangles, and patterns) and dimension measurement items (such as distances and angles).

Distance measurement is used to measure the distance between two features. Specifically, distance measurement can be used to measure point-to-point, point-to-line, point-to-plane, line-to-line, line-to-plane, and plane-to-plane distances between two features. For example, you can select two circle features and choose the center for these two circles to measure the distance between their centers.

Angle measurement is used to measure the angle between two features. Specifically, angle measurements can be used to measure the line-to-line, line-to-plane, and plane-to-plane angles between two features. For example, you can select two circle features and choose the orientation for these two circles to measure the angle between their normals.

Control items refer to the measurement children of measurement items. Control items are used to constrain measurement items. For example, the control items of a circle measurement item include dimension control items (X, Y, Z, and radius), GD&T control items (profile of a surface, parallelism, perpendicularity, position, and concentricity), and custom control items.

In this software, geometric dimensioning and tolerancing (GD&T) measurements are a type of control items developed based on GD&T. GD&T is an international standard used to define the geometric characteristics of a part. It provides a unified set of symbols and language to specify requirements related to the shape, size, location, and orientation of the part.

Position is used to describe the deviation of features such as points, lines, and planes from their ideal positions.

Flatness is used to describe the deviation of a surface from its ideal plane.

Nominal values refer to the ideal or target dimensions of a feature, which are the standard values that the designer expects the part to achieve during the manufacturing process. The nominal values serve as a reference to determine the shape, size, and other design requirements of the part.

Feature picking refers to manually selecting several points of a feature in the central 3D view using the mouse. This is done to determine the position and dimensions of the feature in the view and to pick the nominal values of the feature.

Measured values refer to the actual measurement results of features provided by Mech-MSR and processed by Mech-Metrics. After importing the measured values into Mech-Metrics, the coordinates are transformed according to the newly created reference frame, and all measurement results are expressed and analyzed according to this reference frame.

Tolerance refers to the difference between the maximum and minimum allowable dimensions based on a nominal value. For example, if a cylinder is designed to have a length of 50 mm and a tolerance of ±0.1 mm, it is eligible within the range of 49.9 mm to 50.1 mm.

An annotation card displays data such as nominal values, measured values, and deviations for each sub-item of the measurement item (e.g., X, Y, and Z for a circle measurement item) in a table.

A robot reference frame refers to the reference frame used by the robot to describe positions and orientations. The origin of the robot reference frame is located at the robot base and remains fixed.

A part reference frame is a reference frame established based on certain standards that a specific part of the vehicle body must follow during its processing and manufacturing.

A vehicle reference frame is a reference frame established at the early stages of vehicle design to define the position and orientation of various parts of the vehicle.

Alignment refers to establishing the spatial relationship between different reference frames (such as the robot reference frame and the vehicle body reference frame), so as to accurately transform the measured values in the robot reference frame into those in the vehicle body reference frame or other target reference frames. Alignment is the foundation for unifying the data in multiple reference frames and aligning measurement results.

Part alignment refers to defining a reference frame based on datum features of the part (such as holes, edges, and datum surfaces). Since the reference feature of each part may be different, when a part is used for alignment, the reference frame of each part may also be different. This method can appropriately relax the requirements on the accuracy of fixtures, suitable for scenarios where the reference features of the part are easy to recognize and the fixturing methods vary. The transformation path is as follows: robot reference frame → vehicle body reference frame.

Fixture alignment refers to establishing a reference frame for the fixture (the equipment used to hold the part in place) based on measured features of the fixture. Due to the fixed nature of the fixture, all parts to be measured can be converted to the fixture reference frame by performing alignment once. This method has a high requirement on the accuracy of the fixture, which is suitable for mass production and fixture reuse scenarios. The transformation path is as follows: robot reference frame → vehicle body reference frame.

RPS alignment aligns workpieces accurately with their CAD models by selecting a set of reference feature points that constrain the translation and rotation of the parts. This method is used for part alignment.

Best-fit alignment is the process of aligning a part with the CAD model of the part by performing a best fit with at least three feature center points. This method is used for fixture alignment.

ROI refers to a specific region that is selected for analysis or processing during image processing.

Quality inspection mode refers to the detection range strategy used by the system during measurement tasks. It is used to control the range of measurement items that need to be involved in measurement and judgment in the current task. The Mech-Metrics supports two quality inspection modes: Full inspection and Half inspection. You can switch between them according to the takt time and quality control requirements.

Full inspection refers to the measurement and judgment of all measurement items configured on the current part. The full inspection is applicable to scenarios such as first-piece confirmation, model change verification, anomaly tracing, and periodic comprehensive inspections.

Partial inspection refers to the measurement and judgment of only predefined key measurement items. Partial inspection is suitable for high-frequency process monitoring during the mass production phase. It can ensure that key quality characteristics are controlled while reducing the time required for single-piece inspection.

Repeatability testing refers to performing multiple measurements of the same measurement target or object under the same conditions, to assess the consistency of the measurement results.

In static repeatability testing, the part is fixed in place using a fixture. The robot, equipped with a camera, moves to the measurement position of the part’s feature. At this position, the robot remains still while the camera captures multiple images of the feature. For example, if a part has 5 features, the static repeatability testing is performed as follows:

In semi-dynamic repeatability testing, the part is fixed in place using a fixture, and the robot, equipped with a camera, moves sequentially to the measurement positions of each feature on the part and takes photos. After completing one round of photo captures, the same operation is repeated to complete the remaining rounds. For example, if a part has 5 features, the semi-dynamic repeatability testing is performed as follows:

In dynamic repeatability testing, the process is similar to semi-dynamic repeatability testing, except that the part is re-clamped at the beginning of each measurement round. After the part is clamped and secured, the robot, equipped with a camera, moves sequentially to the measurement positions of each feature on the part and takes photos. For example, if a part has 5 features, the dynamic repeatability test is performed as follows:

Accuracy refers to the closeness or error size between the measurement results and the true value.

Range is a statistical indicator that measures the difference between the maximum and minimum values in a data set. It is used to represent the dispersion of the data.

The 3D tab on the repeatability test results page shows the change trend of the 3D coordinates of the feature points with the number of measurements.

A Programmable Logic Controller, abbreviated as PLC, is a programmable computing device used to manage electromechanical processes, typically applied in industrial fields.

A host computer refers to a computer used in industrial control systems to monitor, manage, and control lower-level devices (such as PLCs, robots, etc.).

A robot is a programmable multi-purpose handling device with some autonomy that can perform tasks such as movement, manipulation, or positioning.

Correlation refers to the degree of consistency between the measurement results of two different measurement devices when measuring the same dimension of the same part.

Correlation analysis and compensation refer to analyzing the relationship between the measurement results of two different measuring devices, followed by compensating the results of one device to improve the reliability of the device.

Temperature drift refers to an offset in measured values caused by temperature changes. In inline measurement scenarios, thermal drift is usually caused by changes in camera, robot, tool, or ambient temperature, and will cumulatively affect measurement stability and accuracy over time.

Temperature drift rods refer to reference rods that are fixedly arranged in an inline measurement unit and on which multiple calibration spheres are mounted. As the relative position between the thermal drift rod and the robot base in space is fixed, it can be used as a reference object for thermal drift compensation.

The thermal drift compensation solution refers to a method in which, with the robot base fixed, a thermal drift rod is installed at a fixed position and its calibration sphere is measured periodically. By leveraging the invariant relative position between the calibration sphere and the robot, the thermal drift compensation model is continuously updated, system parameters (such as robot link lengths and joint position offsets) are corrected, and the updated model is used to compensate in real time for the measurement results at each measurement point on the part.

A Coordinate Measuring Machine (CMM) is a typical coordinate measuring device. Using a measurement platform as a reference, it establishes a mechanical reference frame, collects the coordinates of measurement points on the surface of a part, and projects them into a spatial reference frame to construct a 3D model of the part.

A CMM measurement report refers to a report generated by a coordinate measuring machine (CMM) that records, summarizes, and presents the measurement results of part dimensions and geometric features. Reports usually contain information about the part to be measured, measurement items, nominal values, measured values, deviations, and judgment results. In correlation analysis scenarios, CMM measurement reports are often used as a benchmark for consistency analysis with inline measurement results.

In Mech-Metrics, a sequence refers to a group of actions organized in the order of execution under a measurement event. When the corresponding measurement event is triggered, the system will perform these actions in the order of the current sequence.

A measurement event refers to the moment when the sequence is triggered to execute. For example, both After part measurement start and After part measurement end are measurement events.

Measurement records refer to the measurement data stored in the historical data of the software.

A Pareto chart is a statistical analysis chart that combines bar and line charts to show the importance of various problems or factors to the overall impact. The bars, arranged in descending order, represent the frequencies or values of each class. The line graph shows the cumulative percentage. A Pareto chart is commonly used to identify and prioritize the most significant problems (“the 80/20 rule”), helping users focus on the few key factors that have the greatest impact.

The trend chart displays the trend of the measurement data of each measurement feature along with the number of measurements in the form of a line chart, which helps you visualize the fluctuation and trend of the measured values.

SPC stands for Statistical Process Control, which refers to the use of statistical methods to monitor each stage of the production process in order to ensure and improve product quality.

The Upper Specification Limit, abbreviated as USL, is the upper limit of a dimension, which is the nominal value plus the upper tolerance. For example, if the nominal length of a feature is 5mm and the tolerance is -1 to 1mm, the USL would be 6mm.

The Lower Specification Limit, abbreviated as LSL, is the lower limit of a dimension, which is the nominal value plus the lower tolerance. For example, if the nominal length of a feature is 5mm and the tolerance is -1 to 1mm, the LSL would be 4mm.

σ represents the standard deviation. The 3σ rule, also known as the three-sigma rule, is a method used in statistics to exclude outliers. It assumes that the data follows a normal distribution, and any data point that exceeds the mean plus or minus three standard deviations is considered an outlier and should be removed from the dataset. The 3σ control limits are used to check whether data points lie within three standard deviations of the mean.

The Central Line, abbreviated as CL, is a line consisting of the average values ().

The Upper Control Limit, abbreviated as UCL, is the value obtained by adding 3σ to the average value.

The Lower Control Limit, abbreviated as LCL, is the value obtained by subtracting 3σ from the average value.

A control chart is used to analyze and determine whether a process is in a state of control. It includes control limits. The control chart is based on the 3σ rule in normal distribution, where the central line represents the average value (), and the upper and lower control limits are calculated by adding and subtracting 3σ from the average value. These limits are used to identify if there are any issues occurring in the process.

The Process Performance Index, shortened as Pp, is used to assess whether the performance of a process meets specification requirements. The formula for calculating Pp is as follows. In this example, s represents the standard deviation of the sample.

The central performance index (“Process Performance Index” or Ppk) is used to evaluate whether the performance of a process meets specifications. Compared with Pp, Ppk takes into account the influence of the average process performance. The formula for calculating Ppk is as follows. In the above example, represents the average value of the sample, and s represents the standard deviation of the sample.

The Process Capability Index (Cp) is used to evaluate whether the capabilities of a process meet the requirements. The formula for calculating Cp is as follows. In this example, σ represents the overall standard deviation.

The Central Capability Index (Cpk) is used to evaluate whether the capabilities of a process meet specifications. Compared with Cp, Cpk takes into account the influence of the average process capability. The formula for calculating Cpk is as follows. In the above example, represents the overall average, and σ represents the overall standard deviation.

Measurement report is the official document that summarizes, analyzes, and displays the measurement results of parts. Reports usually contain information about measurement objects, measurement items, measurement data, deviation analysis, tolerance judgment, and statistical analysis. Mech-Metrics supports custom PDF and Table report measurement reports to meet different archiving, sharing, and data processing requirements. Measurement reports are widely used in quality traceability, process control, and delivery scenarios.