Have you ever wondered how precision in manufacturing is achieved down to the micrometer? The Coordinate Measuring Machine (CMM) holds the answer. This advanced device, equipped with high-performance data acquisition systems and air brake switches, ensures exceptional measurement accuracy across industries—from automotive to aerospace. In this article, discover how CMMs operate, their various types, and the incredible precision they bring to product design and quality control. By reading further, you’ll gain insights into the mechanics of CMMs and their critical role in modern manufacturing.
The Coordinate Measuring Machine (CMM) is a precision measuring instrument used in a variety of industries. It is equipped with air brake switches and micro-motion devices on its three axes, enabling precise transmission of each axis. Additionally, the CMM is fitted with a high-performance data acquisition system to ensure accuracy in measurements.
The CMM is commonly used for product design, mold equipment, gear and blade measurements, machinery manufacturing, tooling fixtures, steam mold parts, electronic and electrical equipment, and other precision measurements.
The Three Coordinate Measuring Machine (CMM), also known as the Three Coordinate Measuring Instrument, is a precision metrology device used to measure geometric dimensions, shapes, and spatial relationships within a three-dimensional coordinate system. It operates by utilizing a probe that can move along three orthogonal axes (X, Y, and Z) with high precision.
The probe can either make physical contact with the workpiece (touch-trigger or scanning probes) or perform non-contact measurements (laser or vision systems). The displacement measuring system for each axis, typically employing high-precision linear encoders or optical scales, feeds data to a sophisticated computer system. This system processes the collected points (x, y, z) to calculate various geometric features, dimensions, and form characteristics of the workpiece.
CMMs are capable of measuring multiple aspects of part quality, including:
This versatile instrument is crucial in ensuring precision and accuracy across various industries, including automotive, aerospace, and advanced manufacturing.
Model Specifications:
Structure: Three-axis granite construction with a German-style moving bridge design, featuring four-sided enclosure for enhanced stability.
Drive System: DC servo motors coupled with preloaded high-precision air bearings for smooth, frictionless motion.
Measurement System: RENISHAW open linear encoders with a resolution of 0.1 μm (100 nm).
Probe System: Renishaw controller and probe head, ensuring compatibility and high-performance measurement capabilities.
Base: High-precision (Grade 00) granite surface plate, providing a stable reference surface.
Environmental Requirements:
Pneumatic Requirements:
Performance Specifications:
Key Features:
The machine utilizes natural granite guide rails for all three axes, ensuring superior thermodynamic stability throughout the entire structure. This design choice eliminates accuracy errors that could arise from differential thermal expansion between materials, as might occur in machines using mixed materials for different axes. The uniform thermal characteristics of granite contribute to consistent performance across varying environmental conditions and measurement durations.
Comparison of granite and aviation aluminum alloy
Aluminum alloy materials exhibit a significantly higher coefficient of thermal expansion compared to granite. This inherent property can lead to dimensional instability in precision equipment.
In coordinate measuring machines (CMMs), components such as beams and z-axis structures manufactured from aviation-grade aluminum alloys are susceptible to dimensional changes and accuracy drift over time, particularly with prolonged use and thermal cycling.
In contrast, high-end CMMs often utilize granite for critical structural components. The platform of the three-coordinate system and the main axis are typically constructed from precision-ground granite blocks. This material choice provides superior thermal stability and vibration damping characteristics.
The main shaft is fabricated from granite, while the beam and z-axis may incorporate a hybrid design using aluminum alloys and other materials for optimized weight and stiffness. However, this combination of materials with differing thermal expansion coefficients can potentially introduce measurement errors and stability issues when subjected to temperature fluctuations.
To mitigate these challenges, advanced CMMs employ a fully granite rectangular structure for the three-axis guide system. This design is complemented by high-precision, self-cleaning, prestressed air bearings. The monolithic granite structure ensures long-term dimensional stability and measurement accuracy.
The air bearings provide stable and balanced force distribution along the axial direction, significantly reducing wear and contributing to the longevity of the machine’s critical components. This design also minimizes friction and stick-slip effects, enhancing measurement repeatability.
A patented small-hole air outlet technology is implemented, with an optimized air consumption rate of 30L/min. This innovation creates a localized condensation effect within the bearing clearance, effectively counteracting the heat generated from residual bearing motion friction and enhancing the overall thermal stability of the equipment.
The underlying physical principle leverages the behavior of gas passing through a circular orifice under pressure. While conventional wisdom suggests that this process generates frictional heat, which can be detrimental to high-precision measurements, the small-hole design induces a unique phenomenon. When the outlet hole’s diameter is reduced below a critical threshold, a condensation effect occurs in the immediate vicinity of the orifice. This localized cooling effectively offsets the minimal heat generated by air friction during measurement operations.
By harnessing this physical principle through the implementation of small-hole gas outlet technology, the CMM can maintain exceptional temperature stability over extended periods. This thermal management strategy is crucial for ensuring consistent measurement accuracy and reliability in precision metrology applications.
Comparison of CMM Bearings from Major Suppliers
The three axes incorporate Renishaw’s premium gold-plated optical scales, offering an exceptional resolution of 0.1μm (micrometers). This high-precision linear encoding system ensures accurate position feedback and measurement capabilities.
The scale mounting design employs a fixed-free configuration, with one end securely anchored and the other allowed to float. This arrangement effectively compensates for thermal expansion and contraction, minimizing measurement errors due to environmental temperature fluctuations.
The motion system utilizes a state-of-the-art kinematic design that decouples the drive forces from the bearing surfaces. This advanced approach eliminates induced stresses on the guideways, maximizing both measurement accuracy and long-term mechanical stability.
For axis drive, a steel-reinforced synchronous belt transmission system is employed. This design offers superior vibration damping characteristics during rapid traverses, while simultaneously providing high tensile strength, excellent positioning speed, and extended operational lifespan.
The CMM operates on Rational-DMIS software, an industry-leading metrology package certified by the Physikalisch-Technische Bundesanstalt (PTB). This powerful yet intuitive software platform allows users to focus on measurement tasks rather than complex programming, streamlining the inspection process.
X-beam:
Incorporates advanced precision inclined beam technology, enhancing structural rigidity and minimizing thermal deformation for improved measurement accuracy.
Y-direction guide rail:
Features a proprietary positioning structure with integral lower dovetail grooves directly machined into the workbench, ensuring superior alignment and reducing assembly errors.
Guide rail system:
Utilizes self-cleaning, preloaded high-precision air bearings comprising four-way static pressure air floating guide rails. This design minimizes friction, enhances smoothness of motion, and maintains consistent accuracy over time.
Drive system:
Implements high-performance DC servo motors coupled with flexible synchronous toothed belt drive mechanisms. Each axis is electronically controlled and mechanically limited, resulting in rapid transmission, improved motion performance, and enhanced positioning precision.
Z-axis spindle:
Integrates an adjustable pneumatic balancing device, significantly enhancing the positioning accuracy and repeatability of the z-axis measurements. This feature compensates for probe weight variations and ensures consistent contact force.
Control system:
Employs an advanced imported dual-computer three-coordinate specialized control system, enabling parallel processing and redundancy for improved reliability and performance.
Machine system:
Incorporates Computer Aided 3D error correction technology (CAA), ensuring long-term stability and high accuracy of the system. This adaptive technology compensates for geometric errors and thermal variations in real-time.
Measurement software:
Utilizes the comprehensive 3D-DMIS measurement software package, offering a full spectrum of measurement functions, advanced data analysis capabilities, and seamless online integration with CAD/CAM systems for efficient inspection processes.
A Coordinate Measuring Machine (CMM) is a precision metrology instrument designed to measure the geometric characteristics of objects with high accuracy. It consists of three primary components: a guide mechanism, length measuring elements, and digital display devices, all aligned along three mutually perpendicular axes (X, Y, and Z). The system also includes a worktable to support the measured object, though the size of this table can vary depending on the CMM’s intended applications.
The measuring head, often equipped with a touch-trigger probe or optical sensor, can be moved to specific measurement points either manually or through computer-controlled motorization. As the probe contacts the workpiece (or captures data optically), it generates a trigger signal. Simultaneously, high-precision linear encoders (typically optical scales or glass scales) along each axis measure the exact position of the probe tip in 3D space.
The core functionality of a CMM lies in its ability to accurately determine and display the spatial coordinates of any point within its measurement volume. This is achieved through a sophisticated integration of mechanical precision, sensor technology, and data processing:
Modern CMMs often incorporate advanced features beyond this basic principle, including:
While this describes the fundamental operation of a CMM, it’s important to note that the technology continues to evolve, with developments in areas such as non-contact measurement, multi-sensor systems, and integration with Industry 4.0 concepts further expanding the capabilities and applications of these crucial metrology tools.
According to the structure of CMM, it can be divided into the following categories:
The most commonly used coordinate measuring machine (CMM) is the mobile bridge type.
The axis, the main shaft that moves in the vertical direction, is guided by a box-shaped frame to move along the horizontal beam.
The horizontal beam, which is perpendicular to the axis, is supported at both ends by two columns, forming a “bridge.” The bridge moves along two guide grooves that are perpendicular to the axis on the horizontal plane.
Due to the support provided by struts at both ends of the beam, the mobile bridge type has a lower minimum deflection and higher accuracy compared to the cantilever type.
In the bridge bed type, the main shaft moves in the vertical direction and is guided by a box-shaped frame to move along the beam of the vertical axis. The beam moves along two horizontal guide rails in the axial direction, which are located on the upper surface of the pillars that are fixed on the machine body.
This type is similar to the mobile bridge type, as both ends of the beam are supported, resulting in minimal beam deflection and higher accuracy compared to the cantilever type.
Additionally, only the beam moves in the axial direction, which reduces the overall inertia and makes manual operation easier compared to the mobile bridge type.
The bridge gantry type, also known as the floor-mounted or door type, is different from the bridge bed type in that it is directly fixed to the floor.
This type of structure offers greater rigidity and stability compared to the bed type bridge and is commonly used in larger three-coordinate measuring instruments.
Each shaft is driven by a motor, providing a large measuring range. The operator can also work within the bridge structure.
The fixed bridge type features a main shaft that moves in the vertical direction and is guided by a box-shaped frame to move along the horizontal beam of the vertical axis.
The bridge, or pillar, is fixed on the machine body, while the measuring table moves along the guide rail of the horizontal plane, which is perpendicular to the axis, in the axial direction.
Each shaft is powered by a motor to maintain position accuracy. However, this model is not designed for manual operation.
The L-shaped bridge is designed to reduce the inertia of the bridge as the shaft moves.
Compared to the mobile bridge type, this design has less inertia in its moving components, making it easier to operate. However, it has a lower level of rigidity.
The movable cantilever type features a main shaft that moves in the vertical direction and is guided by a box-shaped frame to move along the horizontal cantilever beam of the vertical axis in the axial direction. The cantilever beam moves along a guide groove on the horizontal plane, which is perpendicular to the shaft.
This type of structure is open on three sides and is convenient for assembling and disassembling workpieces, as they can extend beyond the table. However, the accuracy is lower due to the cantilever design.
The single pillar mobile type features a main shaft that moves in the vertical direction, and the entire pillar moves along the guide groove of the horizontal plane, which is perpendicular to the shaft, connected to the shaft.
The measuring table moves in the axial direction along the guide groove of the horizontal plane, which is perpendicular to the axis.
This type of structure boasts good rigidity in both the measuring table and pillar, leading to minimal deformation. Additionally, the linear scale of each axis is positioned close to the measuring axis, ensuring compliance with Abbe’s theorem.
The single pillar measuring table is of the mobile type, featuring a main shaft that moves in the vertical direction.
The pillar is equipped with a shaft guide groove and is fixed to the measuring instrument body.
During measurement, the measuring table moves along the axis in the direction of the horizontal plane.
The horizontal arm measuring table is of the mobile type, with a box frame that supports the horizontal arm to move in the vertical (axis) direction along the vertical pillar. The probe is attached to the cantilever in the horizontal direction.
The pillar moves in the axial direction along the guide groove in the horizontal plane, which is perpendicular to the axis. The measuring table also moves in the axial direction along the guide groove in the horizontal plane, which is perpendicular to the axis and the axis.
This design is an improvement on the horizontal cantilever type, as it eliminates the deflection caused by the extension or retraction of the horizontal arm in the axial direction.
The horizontal arm measuring platform is of the fixed type and has a similar structure to the mobile type.
The measuring table is fixed, and the X, Y, and Z axes move along the guide groove. During measurement, the pillar moves in the guide groove of the shaft, while the sliding table attached to the shaft moves in the vertical axis direction.
The horizontal arm moving type features a cantilever shaft that moves in the horizontal direction and a box frame that supports the horizontal arm and moves along the column in the axial direction. The column is perpendicular to the axis.
The pillar moves in the axial direction along the guide groove of the horizontal plane, which is perpendicular to the axis, making it unsuitable for high-precision measurements unless the horizontal arm is extended or retracted to compensate for errors caused by weight.
This type of structure is primarily used for vehicle inspection.
The closed loop bridge type is known for its stability, as the driving mechanism is located in the center of the workbench. This design helps reduce the impact caused by bridge movement, making it the most stable among all three-coordinate measuring instruments.
The closed loop bridge type is widely used in a variety of industries, including automobiles, electronics, machinery, aviation, and military, for the measurement of various objects such as boxes, frames, gears, cams, worm wheels, worms, blades, curves, curved surfaces, hardware, plastics, and more. It is also commonly used in the mold industry.
Three-coordinate measuring machines (CMMs) are typically classified into three categories: contact measurement, non-contact measurement, and combined contact and non-contact measurement.
Contact measurement is a commonly used method for measuring machined products, pressed products, and metal films. Scanning data points on the surface of the measured object with a CMM is often necessary for analyzing processing data or for reverse engineering purposes.
Using the Foundation-Pro CMM as an example, this article will describe the different common scanning methods and operation steps for CMMs.
The scanning operation of a CMM involves collecting data points in a specific area on the surface of the object being measured using the PC DMIS program. This area can be a line, patch, section of the part, curve of the part, or circumference at a certain distance from the edge.
The type of scan is dependent on the measurement mode, probe type, and whether CAD files are available. The “scan” option on the control screen is determined by the status button (manual/DCC).
If the DCC method is used for measurement and CAD files are available, the available scanning methods are “open line”, “closed line”, “patch”, “section”, and “perimeter” scanning. If only wireframe CAD files are available, the available scanning methods are “open line”, “closed line”, and “patch” scanning.
If manual measurement mode is used, only the basic “manual TTP scan” mode is available. If manual measurement is used with a rigid probe, the available options are fixed delta, variable delta, time delta, and body axis scan.
This article will provide a detailed explanation of the five scanning modes that can be selected when the “utility” menu is entered and the “scan” option is selected under DCC status.
Open line scanning is the simplest scanning mode. The probe starts from the starting point, scans along a specified direction with a predetermined step size, and ends at the end point.
Open line scanning can be divided into two cases based on the availability of a CAD model.
(1) Without CAD Model:
If the measured workpiece does not have a CAD model, first input the nominal values of the boundary points. Open the “boundary point” option in the dialog box, click “1” to input the data of the starting point. Then, double-click “d” to input the new X, Y, and Z coordinate values of the direction point (the coordinate point indicating the scanning direction). Finally, double-click “2” to input the data of the end point.
Next, input the step size. Enter a new step length value in the “Max Inc” column in the “Direction 1 Tech” column in the scan dialog box. Finally, verify that the set direction vector is correct, which defines the normal vector of the surface of the first measurement point after the start of scanning, the cross-section, and the surface normal vector of the last point before the end of scanning. Click “create” after all the data has been entered.
(2) With CAD Model:
If the measured workpiece has a CAD model, click the corresponding surface of the CAD model with the left mouse button at the start of scanning, and the PC DMIS program will generate a point on the CAD model and mark it as “1”, the starting point. Then, click the next point to define the scanning direction. Finally, click the end point (or boundary point) and mark it as “2”. Connect the line between “1” and “2”.
For each selected point, the PC DMIS program will enter the corresponding coordinate value and vector in the dialog box. After determining the step size and other options (such as safety plane, single point, etc.), click “measure” and then “create”.
Closed line scanning mode allows for the scanning of the inner or outer surface of a workpiece. It only requires two values, the “starting point” and the “direction point” (PC DMIS takes the starting point as the end point).
(1) Data Input Operation:
Double-click the boundary point “1” to enter its position in the edit dialog box. Double-click the direction point “d” to enter its coordinate value. Select the scan type (“linear” or “variable”), enter the step size, and define the touch type (“vector”, “surface”, or “edge”).
Double-click the “initial vector” and enter the vector at point “1”. Verify the section vector. After entering other options, click “create”.
You can also touch the first measuring point on the surface of the workpiece using the coordinate measuring machine’s control panel, then touch the direction point. The PC DMIS program will automatically input the measured value into the dialog box and calculate the initial vector.
After selecting the scanning control mode, measuring point type, and other options, click “create”.
(2) Closed Line Scanning with CAD Model:
If the measured workpiece has a CAD model, confirm “closed line scanning” before measurement. First, click the starting point of the surface to generate symbol “1” on the CAD model (when clicking, the surface and boundary points are highlighted to help select the correct surface). Then, click the scanning direction point.
PC DMIS will provide the corresponding coordinates and vectors of the selected points in the dialog box. After selecting the scanning control method, step size, and other options, click “create”.
The Patch Scanning Mode allows you to scan an area, rather than just a single scanning line.
This scanning method requires at least four boundary point information, including the starting point, direction point, scanning length, and scanning width.
The PC DMIS can calculate the triangular patch based on boundary points 1, 2, and 3, which are defined by the basic or default information. The scanning direction is determined by the coordinate value of point D.
If you add a fourth or fifth boundary point, the patch can be either square or pentagonal in shape.
When using the Patch Scanning Method, make sure to select “Closed Line Scanning” in the checkbox to scan closed elements such as cylinders, cones, grooves, etc. Then, enter the start point, end point, and direction point.
The end point position represents the upward or downward distance moved during the scanning of the measured element.
The section plane vector can be defined by the starting point, direction point, and starting vector (which is typically parallel to the measured element).
Three methods for defining patch scanning are introduced, using the creation of quadrilateral patches as an example:
(1) Coordinate Value Entry:
(2) Touch Testing Mode:
(3) CAD Surface Model Mode:
The Section Scanning mode is only applicable to workpieces with a CAD surface model.
It enables scanning of a specific section of the workpiece.
The scanned section can be along the X, Y, or Z-axis direction or at a specific angle with the coordinate axis.
Multiple section scans can be performed by defining the step size.
You can set the boundary point of the section scan in the dialog box.
By pressing the “Cut CAD” conversion button, you can locate any holes in the CAD surface model and define its boundary line in the same way as Open Line Scanning.
The PC DMIS program will automatically adjust the scanning path to avoid any holes in the CAD surface model.
To cut the CAD surface model by user-defined surface, follow these steps:
At this point, the PC DMIS program will cut the selected surface to find any holes.
If there are no holes defined in the CAD surface model, it’s not necessary to select the “Cut CAD” option. In this case, PC DMIS will scan according to the defined start and end boundary points.
For complex CAD graphics with multiple surfaces, different surfaces can be sectioned in groups. The number of groups is restricted to the local CAD surface models.
The Perimeter Scan method is only applicable to workpieces with a CAD surface model.
This scanning mode uses the CAD mathematical model to calculate the scanning path, which is offset from the boundary or outer contour by a user-selected distance.
To create a boundary scan, follow these steps:
(1) To improve the accuracy of data acquisition and efficiency of measurement, it is important to choose the appropriate scanning measurement mode based on the specific characteristics and modeling requirements of the workpiece being measured.
(2) The clamping position of the workpiece should be planned carefully to facilitate the measurement process and the movement of the probe. To ensure modeling accuracy, try to arrange the probe so that it completes scanning measurements of all objects at once when clamping the workpiece.
(3) The selection of scanning measurement points should include key points of the geometric information of the workpiece’s contour and measurement points should be added appropriately at parts with significant curvature changes.
Tasks and Requirements for Data Conversion:
(1) Convert the measurement data format into the IGES format recognized by CAD software and save it with a product name or a user-specified name after combining.
(2) Data with different products, different attributes, and different positioning that is prone to confusion should be stored in separate files and should be organized and separated in IGES files.
The data conversion is performed by the Coordinate Measurement Data Processing System.
For the operation method, refer to the software user manual.
Application background
During the process of product surveying and mapping, it’s often not possible to measure the product’s geometric data in the same coordinate system for various reasons.
The first reason is that the product size exceeds the measuring machine’s stroke.
The second reason is that the measuring probe cannot reach the opposite side of the product.
The third reason is that data is missing after the workpiece is removed and needs to be re-measured.
In such cases, it’s necessary to measure each part of the product in different positioning states (i.e., different coordinate systems), which is known as Product Relocation Measurement.
In modeling, data from different coordinate systems in different positioning states must be transformed into the same coordinate system, which is called the Integration of Relocation Data.
For complex or large models, multiple positioning measurements are often required in the measurement process.
The final measurement data must be relocated and integrated multiple times according to a specific conversion path, to convert data measured in each positioning into measurement data under a common positioning benchmark.
Relocation integration principle
There is a discrepancy between the measurement data after the workpiece is moved (relocated) and the measurement data before the movement.
To integrate the relocated measurement data into the data before the movement, a shape that can be measured both before and after relocation on the workpiece (referred to as the Relocation Benchmark) must be established. As long as the measurement results of the shape after relocation match the measurement results before relocation through a series of transformations, the relocated measurement data can be integrated into the data before the movement.
The Relocation Benchmark serves as a link in the integration of relocated data.
PID control stands for Proportional, Integral, and Differential control.
P parameter:
The system’s response process to the position error can be determined by analyzing the relationship between the system’s stability, rigidity, and positioning error.
A lower value indicates a more stable system with reduced oscillation, but with weaker rigidity and larger positioning error.
On the other hand, a higher value results in better rigidity and smaller positioning error, but the system may experience oscillation.
I Parameter:
The control of the static positioning error caused by friction and load is determined by the relationship between the control value and the arrival time at the theoretical position.
A lower value results in a longer arrival time.
A higher value increases the likelihood of oscillation at the theoretical position.
D parameter:
The parameter provides stability and damping to the system by avoiding excessive error change.
A lower value results in a faster response of the system to the position error.
A higher value results in a slower response of the system.
To prevent “holiday syndrome” it is necessary to change the management mode of the CMM.
The CMM is composed of complex components, including mechanical parts, electrical control parts, and computer systems.
It is important to properly maintain the CMM while using it to measure workpieces, in order to extend its lifespan.
The following explains the basic maintenance of the CMM from three perspectives.
Mechanical parts
There are various types of mechanical components in a Coordinate Measuring Machine (CMM). To ensure proper functioning, it is important to perform daily maintenance on both the transmission system and air circuit system components.
The frequency of maintenance should be determined based on the operating environment of the CMM. In fine measuring rooms with optimal conditions, regular maintenance is recommended every three months. However, in environments with high levels of dust or where temperature and humidity do not meet the requirements for proper operation, maintenance should be performed on a monthly basis.
For the regular maintenance of measuring machines, the factors affecting the measuring machines should be understood:
Influence of compressed air on measuring machine
To choose an appropriate air compressor, it is advisable to incorporate an additional air tank. This will enhance the longevity and stability of the air compressor’s pressure.
It is important that the initial pressure of the air compressor is higher than the required operating pressure.
When starting the equipment, it is recommended to first activate the air compressor, and then turn on the power supply.
Influence of oil and water on measuring machine
Compressed air is crucial for the smooth functioning of a measuring machine, so it is essential to properly maintain the air circuit.
The following tasks should be performed regularly:
To protect the guide rail of measuring machine, good working habits shall be formed
To ensure the safety of the guide rail, place cloth or rubber padding underneath.
After work or completion of parts, be sure to clean the guide rail.
While using the measuring machine, strive to maintain a consistent ambient temperature in the measuring room as during calibration.
Keep in mind that electrical equipment, computers, and personnel all generate heat. During installation, arrange electrical equipment, computers, etc. to be at a sufficient distance from the measuring machine.
Strictly manage the measuring room and minimize the presence of extra personnel.
The management of the operating environment for high precision measuring machines should be especially stringent.
Influence of air conditioning wind direction on temperature of measuring machine
For the air conditioning in the measuring room, it is best to choose a variable frequency air conditioner.
Variable frequency air conditioning has excellent energy-saving capabilities and, most importantly, strong temperature control abilities. At normal capacity, it can regulate the temperature to within ±1 ℃.
Note that the air from the air conditioner may not be at 20 ℃, and should not be directed directly at the measuring machine. To prevent this, the wind direction may be redirected towards a wall or side, leading to a large temperature difference in the room.
The air conditioner should be installed in a planned manner, blowing air to the main area of the room. The wind direction should be upwards to create a large cycle (not towards the measuring machine) and balance the indoor temperature as much as possible.
If feasible, an air duct can be installed to deliver air to the top of the room through double-layer orifice plates, with the return air outlet at the lower part of the room. This will create irregular airflow and make the temperature control in the measuring room more efficient.
Influence of switching time of air conditioner on temperature of machine room
You are required to activate the air conditioning system at your workplace every morning and turn it off at the end of the day.
Once the temperature in the standby room has stabilized for approximately four hours, the measuring machine’s accuracy will also become stable.
However, this operating procedure significantly hinders the efficiency of the measuring machine, making it challenging to guarantee accuracy during both winter and summer.
This will also have a substantial effect on the measuring machine’s normal stability.
Influence of machine room structure on machine room temperature
To maintain a constant temperature in the measuring machine room, thermal insulation measures should be implemented.
In case there are windows, double-paned windows should be installed and direct sunlight should be avoided.
Using a transition room will help reduce temperature loss.
The air conditioning system in the machine room should be of comparable capacity to that of the surrounding room.
If the machine room is too large or too small, it will present difficulties in temperature control.
In areas with high humidity in the South or during the summer or rainy season in the North, sudden shutdown of the cooling air conditioner can cause rapid condensation of water vapor in the air on the low temperature parts and guide rails of the measuring machine, leading to serious corrosion of the air floats and some parts of the machine, affecting its service life.
Excessive humidity can also cause corrosion or short circuits in the circuit boards of computers and control systems.
Low humidity can severely impact the water absorption of granite and cause deformation.
Dust and static electricity can harm the control system.
Therefore, the humidity in the machine room must be controlled within 60% ± 5%.
Poor sealing and high air humidity in the measuring machine room are the primary causes of high humidity.
In areas with high humidity, the machine room should have better sealing and dehumidifiers should be added if necessary.
To address this, the management mode should be changed from “cleaning before holidays” to “cleaning during work,” and the air conditioner and dehumidifier should be turned on to remove moisture.
Regular cleaning of dust in the computer and control system will reduce or prevent potential problems.
Using standard parts for machine inspection is effective but relatively cumbersome and can only be performed periodically.
A more convenient method is to use a representative part, compile an automatic measurement program, and carry out multiple measurements after verifying the machine’s accuracy.
The results can be calculated according to statistical laws, and a reasonable value and tolerance range can be recorded.
The operator can frequently check this part to determine the machine’s accuracy.
Adjustment of Z-axis balance
The Z-axis balance of the measuring machine is divided into weight and pneumatic balance, which helps balance the weight of the Z-axis and ensures its stable operation.
If the air pressure balance switch is accidentally triggered, the Z-axis will become unbalanced.
To resolve this issue, follow these steps:
Two people can work together to adjust the Z-axis balance until it feels balanced when moving up and down.
The end-of-travel switch serves to protect the machine and establish its home position.
Typically, the end-of-travel switch is either a contact switch or a photoelectric switch.
The contact switch is prone to changing position when manually pushing the shaft, leading to poor contact.
To ensure good contact, the switch position can be properly adjusted.
When using a photoelectric switch, it is important to check that the insert’s position is normal and to regularly remove any dust to maintain its proper operation.
Only individuals who have received training and obtained operational certification are allowed to operate the CMM.
Before starting the machine each day, the control cabinet can only be opened once the air supply pressure meets the requirement: the air supply pressure must be ≥ 0.65 MPa, and the machine air pressure must be ≥ 0.4 MPa.
If the height of the oil-water mixture in the triplet water storage cup exceeds 5mm, the water must be manually drained.
If the machine air supply pressure is normal, but the pressure at the triplet cannot be adjusted to the normal value, the filter element needs to be replaced.
The operating environment for the CMM should have a temperature of 20 ± 2°C and a relative humidity of 40-75%.
The regulated power supply should have an output voltage of 220 ± 10V.
No objects should be placed on the machine’s guide rail.
Do not touch the guide rail’s working surface with your hands.
Before starting the machine each day, clean the three-axis guide rail surface with a high woven pure cotton cloth dipped in anhydrous alcohol, and the machine can only be operated once the guide rail surface is dry.
Alcohol should not be used to clean the painted surface or the grating ruler.
The startup sequence is as follows:
The machine must be returned to the zero point after each startup.
Before returning to the zero point, move the probe to a safe position to ensure that there are no obstacles during the probe’s reset and upward movement in the Z-axis.
When replacing the probe, use the special tools provided with the machine and calibrate the new probe:
If a probe error message dialog box appears, close it (or enter 100.0.0.1 in the web address input column to view the error history and message). This message will be automatically cleared during the next startup.
During manual operation, press the slow key when approaching the sampling point.
When rotating the probe, calibrating the probe, automatically changing the probe, or performing any other operations, ensure that there are no obstacles in the probe’s path of movement.
When the program is not in use or not programmed, set the speed on the operation box to 0.
During the first operation of the program, reduce the speed to 10-30% and monitor whether the operation track meets the requirements.
When handling and placing workpieces, first move the probe to a safe position, and ensure that the workpieces do not collide with the work table, especially the machine’s guide rail surface.
The shutdown sequence is as follows:
Steel standard balls that are not used for an extended period of time should be sealed with oil to prevent rust.
When securing a workpiece with an inlay on the granite work surface, the torque should not exceed 20 Nm.
If any abnormal conditions are detected (excluding error messages related to probe replacement), record the error information displayed by the software, contact the technical service department of Hexcon via fax or telephone, and do not perform inspection or maintenance without guidance and permission.
Do not install any software that is not related to the three coordinates on the computer to ensure the system’s reliable operation.
The air conditioner should be left running 24 hours a day, and its maintenance should be performed in the autumn to ensure the normal operation of the three coordinates.
The three-coordinate measuring machine is commonly referred to as a measuring system that determines the three-dimensional coordinates of the surface points of a workpiece through the relative movement of the probe system and the workpiece.
It is also known as a coordinate measuring machine (CMM) or three-coordinate measuring instrument.
The CMM is a complex measurement system that combines light, machinery, electricity, computer, and control technology, which means there are many factors that can affect the measurement results’ uncertainty.
However, for medium and small coordinate systems, the main factor affecting the measurement results’ uncertainty is deviation from the standard measurement temperature (20°C) of the ambient temperature. To achieve accurate coordinate measurement results, the ambient temperature must be strictly controlled within the range specified by the coordinate machine’s instructions.
The current calibration standard for three coordinates is JJF1064-2000 calibration specification for coordinate measuring machines, which specifies that the calibration items are length measurement indication error and detection error.
It is recommended to calibrate once a year.
The 21-point error is the foundation of the CMM’s accuracy, and its calibration is complex.
Even though it is not specified in the standard, calibration of the 21-point error is necessary under the following circumstances: when accepting a new machine, when the length measurement error calibration result falls outside of the tolerance range, after the coordinate machine has been relocated, and after the coordinate machine has been repaired.
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