The full name of CMM is coordinate measuring machine.
The three axes of the CMM are equipped with air brake switch and micro motion device, which can realize the precision transmission of the single axis and adopt a high-performance data acquisition system.
It is applied to product design, mold equipment, gear measurement, blade measurement, machinery manufacturing, tooling fixtures, steam mold parts, electronic and electrical equipment and other precision measurements.
Three coordinate measuring machine refers to an instrument capable of measuring geometric shape, length and circumferential division within the spatial range of a hexahedron.
It is also called three coordinate measuring instrument.
The coordinate measuring instrument can also be defined as “an instrument with a detector that can move in three directions and can move on three mutually perpendicular guide rails.
The detector transmits signals in contact or non-contact manner.
The displacement measuring system of three axes (such as a grating ruler) calculates the points (x, y, z) and various functions of the workpiece through a data processor or a computer”.
The measuring function of CMM shall include dimensional accuracy, positioning accuracy, geometric accuracy and contour accuracy.
Structure type: three axis granite, German movable bridge structure surrounded by four sides;
Transmission mode: DC servo system + preload high-precision air bearing;
Length measuring system: RENISHAW open grating ruler, with a resolution of 0.1 μm;
Probe system: Renishaw controller, Renishaw probe, Renishaw probe;
Machine: high precision (grade 00) granite platform;
Operating environment: temperature (20 ± 2) ℃, humidity 40% – 70%, temperature gradient 1 ℃/m, temperature change 1 ℃/h;
Air pressure: 0.4 MPa – 0.6 MPa;
Air flow: 25 L/min;
Length accuracy mpee: ≤ 2.1 + L/350（ μm)；
Probe ball accuracy MPEP: ≤ 2.1 μm.
The three-axis adopts natural high-precision granite guide rail, which ensures that the whole has the same thermodynamic performance and avoids the machine accuracy error caused by different thermal expansion coefficients of the three-axis materials.
Comparison of granite and aviation aluminum alloy
- Aluminum alloy material has large thermal expansion coefficient.
Generally, the beam and z-axis made of aviation aluminum alloy materials will be damaged and the accuracy will change after several years of use.
- Since the platform of three coordinates is granite structure, the main axis of three coordinates is also granite material.
The main shaft is made of granite, and the beam and z-axis are made of aluminum alloy and other materials.
When the temperature changes, the measurement accuracy will be distorted and stable due to the different thermal expansion coefficients of the three axes.
The three-axis guide rail adopts the all natural granite all embracing rectangular structure, and is equipped with high-precision self-cleaning prestressed air bearing.
It is the foundation to ensure the long-term stability of the machine accuracy.
At the same time, the bearing force is stable and balanced along the axial direction, which is conducive to ensuring the service life of the machine hardware.
- The patented technology of small hole air outlet is adopted, and the air consumption is 30L / min.
The condensation area is formed in the bearing clearance to offset the heat caused by bearing motion friction and increase the overall thermal stability of the equipment.
According to the physical theory, when the gas passes through the circular hole at a certain pressure, heat will be generated due to the gas friction.
In high-precision measurement, small heat will also affect the stability of accuracy.
When the aperture of the outlet hole is smaller than a certain diameter, condensation effect will be formed around the outlet hole on the contrary!
It is precisely by using this physical principle and the technology of outong small hole gas outlet that the condensation effect just offsets the weak heat generated by the air friction in the measurement, so that the equipment can maintain the temperature stability for a long time, thus ensuring the accuracy stability!
Comparison of CMM bearings of major suppliers
- The three axes adopt the original gold-plated grating ruler from Renishaw, with a resolution of 0.1um;
At the same time, one end is fixed and the other end is free to expand and contract to reduce the deformation of the grating ruler.
- The transmission system adopts internationally advanced design, without any stress deformation of the guide rail, to ensure the accuracy and stability of the machine to the maximum extent.
The steel wire reinforced synchronous belt transmission structure can effectively reduce the vibration during high-speed movement (increase), with high strength, high speed and no wear.
- The software is PTB’s comprehensive certification of the industry benchmark rational-dmis.
It is powerful and easy to learn, so you can focus more on product measurement rather than learning software.
2.Basic components of CMM
Adopt precision inclined beam technology.
Y-direction guide rail:
Adopt the unique positioning structure of integral lower dovetail groove directly processed on the workbench.
Guide rail mode:
Adopt self-cleaning preload high-precision air bearing composed of four-way embracing static pressure air floating guide rail.
The high-performance DC servo motor and flexible synchronous toothed belt drive device are adopted.
Each shaft is limited and electronically controlled, so that the transmission is faster and the motion performance is better.
Adjustable pneumatic balance device improves the positioning accuracy of z-axis.
Adopt imported dual computer three coordinate special control system.
Computer Aided 3D error correction technology (CAA) is adopted to ensure long-term stability and high accuracy of the system.
The powerful 3D-DMIS measurement software package is adopted, with perfect measurement function and online function.
3. Functional principle of CMM
To put it simply, CMM is a kind of measuring equipment with guide mechanism, length measuring element and digital display device in three mutually perpendicular directions, and a worktable capable of placing workpieces (large and large may not necessarily exist).
The measuring head can be moved to the measured point in a manual or motorized manner, and the coordinate value of the measured point is displayed by the reading device and digital display device.
Obviously, this is the simplest and most primitive measuring machine.
With this measuring machine, the coordinate value of any point in the measuring volume can be displayed by the reading device and the digital display device.
The sampling point sending device of the measuring machine is a measuring head, and a grating ruler and a reading head are installed along the X, Y and Z axes.
The measuring process is that when the probe contacts the workpiece and sends out the sampling point signal, the control system collects the coordinate value of the current three-axis coordinate of the machine tool relative to the origin of the machine tool, and then the computer system processes the data.
4. Classification of CMM
According to the structure of CMM, it can be divided into the following categories:
1. Moving bridge type
Mobile bridge type is the structure of the most commonly used CMM.
The axis is the main shaft moving in the vertical direction, and the box shaped frame guides the main shaft to move in the direction along the horizontal beam.
The horizontal beam is vertical to the axis and supported at both ends by two columns. The beam and the column form a “bridge”.
The bridge moves in the axial direction along two guide grooves perpendicular to the axis on the horizontal plane.
Because the two ends of the beam are supported by struts, the minimum deflection can be obtained and the accuracy is higher than that of the cantilever type.
2. Bridge bed type
In bridge bed type, the shaft is the main shaft moving in the vertical direction, the box-shaped frame guides the main shaft to move along the beam of the vertical axis, and the beam moves along the two horizontal guide rails in the axial direction.
The guide rail is located on the upper surface of the pillar, and the pillar is fixed on the machine body.
This type is the same as the mobile bridge type. Both ends of the beam are supported, so the deflection of the beam is minimal.
The accuracy of this type is better than that of the cantilever type.
Because only the beam moves in the axial direction, the inertia is smaller than that of the whole bridge.
It is easier to operate manually than that of the movable bridge type.
3. Gantry type
Compared with the bridge bed type, the bridge gantry type is directly fixed on the floor, also known as the door type.
It has greater and better rigidity than the bed type bridge, and most of it is used in the larger three coordinate measuring instrument.
Each shaft is driven by a motor, and the measuring range is large.
The operator can work in the bridge.
4. Fixed bridge type
The shaft of the fixed bridge type is the main shaft moving in the vertical direction, and the box-shaped frame guides the main shaft to move along the horizontal beam of the vertical axis.
The bridge (pillar) is fixed on the machine body, and the measuring table moves in the axial direction along the guide rail of the horizontal plane and is perpendicular to the and axis.
Each shaft is driven by a motor to ensure position accuracy.
This model is not suitable for manual operation.
5. L-shpaed bridge type
The L-shaped bridge is designed to minimize the inertia of the bridge when the shaft moves.
Compared with the mobile bridge type, the mobile components have less inertia, so the operation is easier, but the rigidity is poor.
6. Fixed table cantilever arm type
The shaft is movable cantilever type.
The shaft is the main shaft moving in the vertical direction.
The box shaped frame guides the main shaft to move in the axial direction along the horizontal cantilever beam of the vertical axis.
The cantilever beam moves in the axial direction along the guide groove on the horizontal plane and is perpendicular to the shaft and the shaft.
This type is open on three sides, easy to assemble and disassemble workpieces, and workpieces can extend out of the table to accommodate larger workpieces, but the accuracy is not high due to cantilever.
7. Single column movable type
Single pillar mobile type, the shaft is the main shaft moving in the vertical direction, the whole pillar moves on the shaft along the guide groove of the horizontal plane, and is vertical to the shaft, and the shaft is connected to the pillar.
The measuring table moves on the axis along the guide groove of the horizontal plane and is perpendicular to the axis.
This type of measuring table and pillar have good rigidity, so there is less deformation.
Moreover, the linear scale of each axis is close to the measuring axis, so as to comply with Abbe’s theorem.
8. Single column xy table type
The single pillar measuring table is mobile type.
The shaft is the main shaft moving in the vertical direction.
The pillar is attached with a shaft guide groove, and the pillar is fixed on the measuring instrument body.
During measurement, the measuring table moves along the axis and the axis direction on the horizontal plane.
9. Moving table horizontal arm type
The horizontal arm measuring table is mobile type, and the box frame supports the horizontal arm to move in the vertical (axis) direction along the vertical pillar.
The probe is mounted on the cantilever in the horizontal direction.
The pillar moves in the axial direction along the guide groove in the horizontal plane and is vertical to the axis.
The measuring table moves in the axial direction along the guide groove in the horizontal plane and is perpendicular to the axis and the axis.
This is an improved design of the horizontal cantilever type, in order to eliminate the deflection caused by the extension or retraction of the horizontal arm in the axial direction.
10. Fixed table horizontal arm type
The horizontal arm measuring platform is a fixed type, and its structure is similar to that of the mobile type.
This type of measuring table is fixed, and the X, Y and Z axes move in the guide groove.
During measurement, the pillar moves in the guide groove of the shaft, while the shaft sliding table moves in the vertical axis direction.
11. Horizontal arm moving type
Horizontal arm moving type, the shaft cantilever moves in the horizontal direction, the box frame supporting the horizontal arm moves along the column in the axial direction, and the column is vertical to the axis.
The pillar moves in the axial direction along the guide groove of the horizontal plane and is perpendicular to the axis, so it is not suitable for high-precision measurement.
Unless the horizontal arm is extended or retracted to compensate for the error caused by the weight.
In most cases, it is applied to vehicle inspection.
12. Ring bridge type
Closed loop bridge type, because its driving mode is in the center of the workbench, can reduce the impact caused by the bridge movement, and is the most stable one of all three coordinate measuring instruments.
5. Main advantages
- Surface anodized aviation aluminum alloy;
- High precision self-cleaning air bearing;
- High precision European imported grating ruler;
- Patented technology of precision triangle beam.
6. Application Fields
It is widely used in the measurement of boxes, frames, gears, cams, worm wheels, worms, blades, curves, curved surfaces, hardware, plastics and other industries in the automobile, electronics, machinery, automobile, aviation, military industry, mold and other industries.
7. Method of use
Three coordinate measuring machine (CMM) can generally be divided into contact measurement, non-contact measurement and contact & non-contact measurement.
Among them, the contact measurement method is commonly used for the measurement of machined products, pressed products, metal films, etc.
In order to analyze the processing data of the workpiece or provide the original information of the workpiece for reverse engineering, it is often necessary to scan the data points on the surface of the measured workpiece with a CMM.
Taking the foundation-pro CMM as an example, this paper introduces several common scanning methods and operation steps of CMM.
The scanning operation of CMM is to use PC DMIS program to collect data points in a specific area on the surface of the measured object.
The area can be a line, a patch, a section of the part, a curve of the part or a circumference at a certain distance from the edge.
The scan type is related to the measurement mode, probe type and whether there are CAD files. The “scan” option on the control screen is determined by the status button (manual / DCC).
If DCC method is adopted for measurement and CAD files are available, the scanning methods available are “open line”, “closed line”, “patch”, “section” and “perimeter” scanning;
If DCC method is adopted for measurement, and only wireframe CAD files are available, the “open line”, “closed line” and “patch” scanning methods can be selected;
If manual measurement mode is adopted, only the basic “manual TTP scan” mode can be used;
If manual measurement is adopted and rigid probe is used, the available options are fixed Delta, variable Delta, time delta and body axis scan.
The following describes in detail the five scanning modes that can be selected after entering the “utility” menu and selecting the “scan” option under DCC status.
1.Open Linear Scan
Open line scanning is the most basic scanning mode.
The probe starts from the starting point, scans along a certain direction and in a predetermined step until the end point.
Open line scanning can be divided into two cases with or without CAD model.
(1) No CAD model
If the measured workpiece has no CAD model, first input the nominal value of boundary points.
After opening the “boundary point” option in the dialog box, click “1” to input the data of the scanning start 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 scanning end point.
The second item is the input step size.
Enter a new step length value in the max Inc column in the direction 1 tech column in the scan dialog.
Finally, check whether 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 data are 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 beginning of scanning, and the PC DMIS program will generate a point on the CAD model and mark “1” as the scanning 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, PC DMIS has entered 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 click “create”.
2. Closed Linear Scan
The closed line scanning mode allows scanning of the inner surface or the outer surface.
It only needs two values of “starting point” and “direction point” (the PC DMIS program takes the starting point as the end point).
(1) Data input operation
Double click the boundary point “1” to enter the position in the edit dialog box;
Double click the direction point “d” to enter the coordinate value;
Select the scan type (“linear” or “variable”), enter the step size, and define the touch type (“vector”, “surface” or “edge”);
Double click “initial vector”, enter the vector at “1” point, and check the section vector;
After typing other options, click “create”.
You can also touch the first measuring point on the surface of the workpiece to be measured with the operation panel of the coordinate measuring machine, and then touch the direction point.
The PC DMIS program will automatically put the measured value into the dialog box and automatically 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 the symbol “1” on the CAD model (when clicking, the surface and boundary points are highlighted to select the correct surface);
Then click the scanning direction point;
PC DMIS will give the corresponding coordinates and vectors of the selected position points in the dialog box;
After selecting the scanning control method, step size and other options, click “create”.
3. Patch scan
The patch scanning mode allows scanning an area instead of a scanning line.
The application of this scanning method requires at least four boundary point information, i.e. starting point, direction point, scanning length and scanning width.
The PC DMIS can determine the triangular patch according to the boundary points 1, 2 and 3 given by the basic (or default) information, and the scanning direction is determined by the coordinate value of D;
If the fourth or fifth boundary point is added, the patch can be square or pentagon.
When the patch scanning method is adopted, select “closed line scanning” in the check box to scan a closed element (such as cylinder, cone, groove, etc.), and then enter the start point, end point and direction point.
The end point position represents the distance moved upward or downward when scanning the measured element;
The section plane vector can be defined by the starting point, the direction point and the starting vector (usually the vector is parallel to the measured element).
Taking the creation of quadrilateral patches as an example, several definition methods of patch scanning are introduced:
(1) Type coordinate values
Double click the boundary point “1” and enter the starting point coordinate values X, Y and Z;
Double click the boundary direction point “d” to enter the coordinate value of the scanning direction point;
Double click the boundary point “2” and enter the scan width to determine the first direction;
Double click the boundary point “3” and enter the scan width to determine the second direction;
Click “3”, then press “add” button, and the fourth boundary point will be displayed in the dialog box;
Double click the boundary point “4” and enter the coordinate value of the end point;
After selecting the step size (step size between points) and the maximum step size (step size between points 1 and 2) required for scanning, click “create”.
(2) Touch testing mode
Select the “patch scanning” mode, and touch the first point at the required starting point with the coordinate measuring machine’s straw tray.
The coordinate value of this point will be displayed in the “# 1” item of the “boundary point” dialog box;
Then touch the second point, which represents the end point of the first scanning direction, and its coordinate value will be displayed in the “d” item of the dialog box;
Then touch the third point, which represents the width of the scanned patch, and its coordinate value will be displayed in the “# 3” item of the dialog box;
Click “3” and select “add” to add the fourth point to the list;
Touch the end point and the dialog box will be closed.
Finally, two direction data of scanning line spacing and step length are defined;
After selecting the scanning touch type and the required options, click “create”.
(3) CAD surface model mode
This scanning method is only applicable to the workpiece with CAD surface model.
First, select the “patch scanning” mode, and left click the CAD working surface;
Highlight “1” in the “boundary point” dialog box, and left click the scanning start point on the surface;
Then highlight “d” and click the surface to define the direction point;
Click the surface to define the scanning width (# 2);
Click the surface to define the width on the scan (# 3);
Click “3”, select “add”, add the additional point “4”, highlight “4”, click to define the scanning end point, and close the dialog box.
After defining the steps in both directions and selecting the required options, click “create”.
4. Section Scan
The section scanning mode is only applicable to the workpiece with CAD surface model.
It allows scanning of a certain section of the workpiece.
The scanning section can be along the X, Y, Z axis direction or at a certain 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.
Press the “cut CAD” conversion button, you can find any hole in the CAD surface model, and define its boundary line in the same way as open line scanning.
Pcdmis program will automatically make the scanning path avoid the hole in the CAD surface model.
The method of cutting CAD by user-defined surface is as follows: enter the “boundary point” option;
Enter the “CAD element selection” box;
Select the surface;
Select the cut CAD option without clearing the CAD element selection box.
At this time, the PC DMIS program will cut the selected surface to find holes.
If there is no hole defined in the CAD surface model, it is not necessary to select the “cut CAD” option.
At this time, 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, * # restricts sectioning to local CAD surface models.
5. Perimeter scan
The perimeter scan method is only applicable to the workpiece with CAD surface model.
The scanning mode uses CAD mathematical model to calculate the scanning path, which is offset from the boundary or outer contour by a certain distance (selected by the user).
When creating a boundary scan, first select the “boundary scan” option;
If it is an internal boundary scan, select “internal boundary scan” in the dialog box;
When selecting a working surface, start the “select” check box, highlight one for each selected surface, and exit the check box after selecting all desired surfaces;
Click the surface to determine the scanning starting point;
Click on the same surface to determine the scanning direction point;
Click the surface to determine the scanning end point.
If no end point is given, the start point is the end point;
Enter corresponding values in the “scan structure” edit box (including “value added”, “CAD tolerance”, etc.);
Select the “calculate boundary” option to calculate the scan boundary;
After confirming that the deviation value is correct, press the “generate measuring point” button, and the PC DMIS program will automatically calculate the theoretical value of the scanning; Click “create”.
6. Application points
(1) According to the specific characteristics and modeling requirements of the measured workpiece, the appropriate scanning measurement mode shall be reasonably selected to improve the data acquisition accuracy and measurement efficiency.
(2) In order to facilitate the measurement of the grass work and the movement of the probe, the clamping position of the measured workpiece should be reasonably planned;
In order to ensure the modeling accuracy, when clamping the workpiece, try to make the probe complete the scanning measurement of all measured objects at one time.
(3) The selection of scanning measurement points shall include the key points of the geometric information of the workpiece contour, and the measurement points shall be appropriately added at the parts with obvious curvature changes.
8. Data management
1. Data conversion
Tasks and requirements of data conversion:
(1) Convert the measurement data format into IGES format recognized by CAD software, and save it by product name or user specified name after combination.
(2) Data with different products, different attributes, different positioning and easy to be confused shall be stored in different files and shall be layered and separated in IGES files.
The data conversion is completed by the coordinate measurement data processing system.
See the software user’s Manual for the operation method.
2. Relocation and integration
In the process of product surveying and mapping, it is often impossible to measure the geometric data of the product in the same coordinate system.
The first reason is that the product size exceeds the stroke of the measuring machine;
The second reason is that the measuring probe cannot touch the opposite side of the product; The third reason is that the data is missing after the workpiece is removed and needs to be measured.
At this time, it is necessary to measure each part of the product under different positioning states (i.e., different coordinate systems), which is called product relocation measurement.
In modeling, the relocation data in different coordinate systems should be transformed into the same coordinate system.
This process 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 certain conversion path to convert the data measured in each positioning into measurement data under a common positioning benchmark.
Relocation integration principle
There is a displacement dislocation between the measurement data after the workpiece is moved (relocated) and the measurement data before the movement.
If we determine a shape that can be measured before and after the relocation on the workpiece (referred to as the relocation benchmark), then as long as the measurement results of the shape after the relocation coincide with the measurement results before the relocation through a series of transformations after the completion of the measurement, the measurement data after relocation can be integrated into the data before coincidence.
Relocation benchmark plays a role as a link in relocation integration.
PID control is the abbreviation of proportional, integral and differential control.
Determine the whole response process of the system to the position error.
The lower the value, the more stable the system is, without oscillation, but with poor rigidity and large positioning error;
The higher the value, the better the rigidity and the smaller the positioning error, but the system may produce oscillation.
Control the static positioning error caused by friction and load.
The lower the value, the longer the arrival time;
The higher the value, the more likely it is to oscillate up and down at the theoretical position.
This parameter provides damping and stability to the system by preventing overshoot of error change.
The lower the value, the faster the response of the system to the position error;
The higher the value, the slower the system response.
9. Daily maintenance
Change the management mode to prevent “holiday syndrome”.
The composition of CMM is complex, mainly including mechanical parts, electrical control parts and computer systems.
At ordinary times, when we use the CMM to measure the workpiece, we should also pay attention to the maintenance of the machine to extend the service life of the machine.
Next, we will explain the basic maintenance of CMM from three aspects.
There are many kinds of mechanical components of the CMM.
We need to maintain the components of the transmission system and the air circuit system on a daily basis.
The frequency of maintenance should be determined according to the environment where the CMM is located.
Generally, for measuring machines in fine measuring rooms with good environment, we recommend that regular maintenance be carried out every three months.
If the user’s operating environment is dusty and the temperature and humidity in the measuring room cannot fully meet the requirements of the measuring machine’s operating environment, regular maintenance should be carried out once a month.
For the regular maintenance of measuring machines, the factors affecting the measuring machines should be understood:
Influence of compressed air on measuring machine
- To select a suitable air compressor, it is better to have another air tank to ensure long service life and stable pressure of the air compressor.
- The starting pressure of the air compressor must be greater than the working pressure.
- When starting the machine, first turn on the air compressor and then turn on the power.
Influence of oil and water on measuring machine
Since compressed air plays a very important role in the normal operation of the measuring machine, it is very important to repair and maintain the air circuit.
There are the following main projects:
Check the pipes and filters before using the measuring machine every day, and drain the water and oil in the filter and the air compressor or air tank.
Generally, the filter elements of the attached filter and the prefilter shall be cleaned within 3 months.
The period of poor air quality shall be shortened.
Because the filter element of the filter is also blocked by oil pollution while filtering oil and water, the actual working air pressure of the measuring machine will be reduced if the time is a little longer, and the normal operation of the measuring machine will be affected.
Be sure to clean the filter element regularly.
Wipe the oil stain and dust of the guide rail every day to keep the air floating guide rail in normal working condition.
To protect the guide rail of measuring machine, good working habits shall be formed
Use cloth or rubber to pad under to ensure the safety of the guide rail.
Wipe the guide rail after the work or after the parts are finished.
When we use the measuring machine, we should try to keep the ambient temperature of the measuring machine room consistent with that during verification.
In addition, electrical equipment, computers and personnel are all heat sources.
During equipment installation, planning shall be made to ensure that electrical equipment, computers, etc. have a certain distance from the measuring machine.
Strengthen the management of the measuring machine room and do not have redundant personnel.
The management of the use environment of high-precision measuring machines should be more strict.
Influence of air conditioning wind direction on temperature of measuring machine
Variable frequency air conditioner shall be selected as far as possible for the air conditioner of the measuring machine room.
Variable frequency air conditioning has good energy-saving performance, and the most important thing is strong temperature control ability.
Under normal capacity, the temperature can be controlled within ± 1 ℃.
Since the temperature of the air blown by the air conditioner is not 20 ℃, the air must not be blown directly to the measuring machine.
Sometimes, in order to prevent the wind from blowing on the measuring machine, the wind direction is turned to the wall or one side.
As a result, the temperature difference in the machine room is very large.
The air conditioner shall be installed in a planned way. The air shall be blown to the main position of the room.
The wind direction shall be upward to form a large cycle (not to the measuring machine), and the indoor temperature shall be balanced as much as possible.
If conditions permit, an air duct shall be installed to send the air to the top of the room for air supply through double-layer orifice plates, and the return air outlet shall be at the lower part of the room.
This makes the airflow flow irregularly and makes the temperature control of the machine room more reasonable.
Influence of switching time of air conditioner on temperature of machine room
You need to turn on the air conditioner at work every morning and turn off the air conditioner after work at night.
After the temperature of the standby room is stable for about 4 hours, the accuracy of the measuring machine can be stable.
This working mode seriously affects the efficiency of the measuring machine, and it is difficult to ensure the accuracy in winter and summer.
It will also have a great impact on the normal stability of the measuring machine.
Influence of machine room structure on machine room temperature
Since the measuring machine room requires constant temperature, the machine room shall be provided with thermal insulation measures.
If there are windows, double-layer windows shall be adopted and sunlight shall be avoided.
The transition room shall be used as far as possible to reduce the temperature loss.
The air conditioning selection of the machine room shall be comparable to that of the room.
If the machine room is too large or too small, it will cause difficulties in temperature control.
In the areas with high humidity in the South or in the summer or rainy season in the north, when the cooling air conditioner is suddenly shut down, the water vapor in the air will quickly condense on the guide rails and parts of the measuring machine with relatively low temperature, which will cause serious corrosion of the air floats and some parts of the measuring machine and affect the service life of the measuring machine.
The circuit boards of computers and control systems may corrode or cause short circuit due to excessive humidity.
If the humidity is too low, it will seriously affect the water absorption of granite and may cause deformation of granite.
Dust and static electricity can cause harm to the control system.
Therefore, the humidity of the machine room is not insignificant. It should be controlled within the range of 60% ± 5%.
High air humidity and poor sealing of the measuring machine room are the main reasons for high humidity of the machine room.
In areas with high humidity, the sealing of the machine room shall be better, and dehumidifiers shall be added if necessary.
The solution is to change the management mode, change “cleaning before holidays” to “cleaning at work”, and turn on the air conditioner and dehumidifier to remove water.
Regularly clean the dust in the computer and control system to reduce or avoid the potential trouble caused by this.
It is very good to use standard parts to check the machine, but it is relatively troublesome and can only be done once a period of time.
A more convenient method is to use a typical part, compile an automatic measurement program, and carry out multiple measurements under the condition that the machine accuracy is verified.
The results are calculated according to the statistical law, and a reasonable value and tolerance range are recorded.
The operator can often check this part to determine the accuracy of the machine.
Adjustment of Z-axis balance
The Z-axis balance of the measuring machine is divided into weight balance and pneumatic balance, which is mainly used to balance the weight of the Z-axis and make the z-axis drive stable.
If the air pressure balance switch is actuated by mistake, the z-axis will lose balance.
- Turn the angle of the measuring base to 90 ° to avoid touching the measuring head during operation.
- Press the “emergency stop” switch.
- One person holds the z-axis with both hands, pushing up and pulling down to feel the effect of balance.
- One person adjusts the air pressure balance valve, and the adjustment amount is a little smaller each time.
Two people can cooperate to adjust the z-axis balance to the same feeling of upward and downward.
The end of travel switch is used for the end of travel protection and home of the machine.
The end of travel switch generally uses a contact switch or a photoelectric switch.
The switch type is most easy to change the position when pushing the shaft by hand, resulting in poor contact.
The switch position can be adjusted properly to ensure good contact.
The photoelectric switch should pay attention to check that the position of the insert is normal, and regularly remove the dust to ensure its normal operation.
10. Use and safety precautions of CMM
- Personnel who have not received training and obtained operation qualification are prohibited from using the CMM.
- The control cabinet can be opened only after the air supply pressure meets the requirements before startup every day: the air supply pressure is ≥ 0.65Mpa, and the machine air pressure is ≥ 0.4MPa.
- When the height of the oil-water mixture in the triplet water storage cup exceeds 5mm, it is necessary to manually drain the water.
When the air supply pressure of the machine is normal, but the pressure at the triplet cannot be adjusted to the normal value, the filter element needs to be replaced.
- CMM operating environment: temperature 20 ± 2 ℃, relative humidity 40-75%.
- The output voltage of the regulated power supply is 220 ± 10V.
- No objects shall be placed in the guide rail of the machine.
Do not directly touch the working surface of the guide rail with your hands.
Clean the three-axis guide rail surface with high woven pure cotton cloth dipped with anhydrous alcohol before starting the machine every day.
The machine can only be operated after the guide rail surface is dry.
It is forbidden to clean the painted surface and grating ruler with alcohol.
- The startup sequence is as follows: open ① power box; ② Total air source; ③ Cold dryer; ④ Air valve; ⑤ Power supply of control cabinet; ⑥ Pedestal controller; ⑦ Power up the motor when the operation box light is on (the emergency stop key must be released); ⑧ After the self inspection of the system is completed, start the measurement software, zero the three axes (go home) “OK”, and enter the normal working state after automatic completion.
- Return to the zero point of the machine after each startup.
Before returning to the zero point, move the probe to the safe position to ensure that there is no obstacle when the probe resets and rotates and moves upward in the z-axis.
- When replacing the probe, use the special tools provided with the machine. The probe used needs to be calibrated:
① When the measurement software is not opened, start the software after replacement. This method is recommended.
② When the measuring software is turned on, the operation box needs to press the emergency stop key switch and turn on the switch after replacement.
The probe error message dialog box will appear.
Close it (or enter 184.108.40.206 in the web address input column to enter the errors history to view the error message).
This message will be automatically cleared when the next boot.
- Under manual operation, when approaching the sampling point, press the slow key.
- When rotating the probe, calibrating the probe, automatically changing the probe, operating procedures and other operations, ensure that there is no obstacle on the running route of the probe.
- When the product is programmed or not used, the speed on the operation box is set to 0.
- During the first operation of the program, reduce the speed to 10 ~ 30%, and pay attention to whether the operation track meets the requirements.
- When carrying and placing workpieces, first move the probe to a safe position, and pay attention that the workpieces cannot collide with the work table, especially the guide rail surface of the machine.
- The shutdown sequence is as follows:
① move the z-axis to the left, front and top of the machine, and rotate the probe angle to A0B0;
② Clean the work surface;
③ Turn off the pedestal controller, the power supply of the control cabinet, the air valve, the dryer, the main air source and the power box in turn.
- The steel standard ball that is not used for a long time needs oil seal for rust prevention.
- When fixing the workpiece with the inlay on the granite worktop, the torque shall not exceed 20nm.
- If any abnormality is found (except for the error information of replacing the probe), please first record the error information prompted by the software, fax or telephone the technical service department of hexcon, and do not carry out inspection and maintenance without guidance and permission.
- Do not install any software irrelevant to the three coordinates in the computer to ensure the reliable operation of the system.
- The air conditioner shall be started 24 hours a day, and the maintenance of the air conditioner shall be carried out in autumn, so as to ensure the normal use of the three coordinates.
FAQs about CMM machine
What is CMM?
The three coordinate measuring machine is usually referred to a measuring system that detects the three-dimensional coordinates of the workpiece surface points through the relative movement of the probe system and the workpiece.
Its English name is coordinate measuring machine (CMM), also known as three coordinate measuring instrument or three dimensional element.
Does the temperature have a great influence on the measurement results of the CMM?
CMM is a complex measurement system integrating light, machinery, electricity, computer and control technology, so there are many factors affecting the uncertainty of its measurement results.
However, for medium and small coordinates, the deviation of ambient temperature from the standard measurement temperature (20 ℃) is the main factor affecting the uncertainty of its measurement results. In order to obtain accurate results of coordinate measurement, the ambient temperature shall be strictly controlled within the range required by the instructions of coordinate machine.
What items of CMM need to be calibrated and how long is the re calibration interval?
At present, the calibration basis of three coordinates is JJF1064-2000 calibration specification for coordinate measuring machines, which stipulates that the calibration items are: length measurement indication error and detection error.
It is suggested that the interval between the resumption of school is one year.
When does the CMM need to calibrate 21 errors?
The 21-item error is the basis of the accuracy of CMM, and its calibration is complex.
Although not listed in the specification, the calibration of 21 errors is necessary under the following conditions: acceptance of new machine; when the length measurement error calibration result is out of tolerance; after the coordinate machine is moved; after the coordinate machine is repaired.