Accurate CNC - New Models
We have the pleasure to present you our new models, loaded with new technologies, extremely high precision and new level of absolute accuracy. After years of R&D; we have systems with unmatched accuracy, following our main goal:
"to build the most accurate PCB prototyping mill"!
Here are our new models:
- Servo models (A63x & A43x): A637, A636, A437, A436, A632, A631, A432, A431,
- Calibrated screw models (A42x & A62x): A627, A626, A427, A426, A622, A621, A422, A431.
Servo models A63x and A43x series are equipped with precision linear encoders and have the following accuracy specifications:
- Absolute accuracy 5 μm @ 254 mm (0.2 mil @ 10 inch)
- Positioning repeatability 1 μm (0.039 mil)
- Internal resolution 0.1 μm (0.0039 mil)
Calibrated screws models A42x and A62x have the following accuracy specifications:
- Absolute accuracy 7.5 μm @ 254 mm (0.3 mil @ 10 inch)
- Positioning repeatability 1.5 μm (0.059 mil)
- Internal resolution 0.1 μm (0.0039 mil)
In order to achieve the accuracy mentioned above, all new models are equipped with thermal compensation:
- for the screws on A42x & A62x models
- for the linear encoders on A63x & A43x models
- for the material under machining on all models
All software and firmware components of our systems are under complete control of our updates and improvements.
- PhCNC™ our control and CAM software
- PhCNC360™, the firmware of our CNC controller
- PhACdrive™, the firmware of our AC/BLDC spindle drive
- PhSTdrive™, the firmware of our X,Y,Z intelligent stepper drives
This allow us to be in full control of the machine operations and achieving our main goal: "to build the most accurate PCB prototyping mill".
A complete list of our models is shown below:
All models are equipped with precision linear gauge for tool penetration control (our CAST™ control) maintaining the desired tool penetration within the accuracy of +/- 1μm (0.039mil) in reference to the material surface.
All of our systems are made in US, using local high quality materials and components.
There is no other (LPKF, MITS, T-TECH, ...) offer on the market currently that comes even close to the accuracy and precision that our models offer!
Thermal compensation, calibrated screws, linear encoders
In order to clarify our efforts "to build the most accurate PCB prototyping mill", we are showing below the typical calibration graphics of a high quality lead screw (similar lead screws are used by all manufacturers/competitors in this business).
The graphics shows the absolute positioning error along the length of the screw.
It is visible that the error consist of two components:
- error from the screw by it self, related to the production of the screw and nonlinearity of the driving motor (we will call this - screw error)
- screw thermal expansion error
Most of the screws specifications are given at 68 °F (20 °C), but actually they never work at this temperature. In fact different axes has different screw temperatures etc. all related to the particular machine design.
Absolute positioning errors at 36°C(97°F) & 20°C (68°F)
As it is seen on the graphics both error components affect the accuracy differently:
- The screw error affect mostly small distance movements and may reach 25 μm @ 2.54 mm (1 mil @ 100 mil). It is quite logical that it has repeat equal to one screw turn.
- The thermal expansion error is quite linear and affect the accuracy in the long distance movements. Here it reaches 110 μm @ 381 mm (4.3 mil @ 15 inch)
The material under machining also has its own thermal expansion that has to be compensated in order to achieve maximum accuracy at desired temperature.
As it is seen from the diagrams rotational encoder or servo control using one is not a solution.
We resolve the problem two ways, designing two different positioning systems that are using linear encoders.
The first one has the encoders permanently mounted and works using servo feedback from them. The encoders have 1μm resolution and better than 10 μm @ 1000 mm @ 68°F (20°C) accuracy. This positioning system shows less than 5μm positioning error @ 254 mm (10 inch). The measuring reference is quartz glass ruler with NIST certificate and 0.2μm accuracy @ 68°F (20°C).
The second one is based on the same encoders, but they are mounted temporary during the production cycle of the system. A calibration procedure is applied and it records the difference (the error) of the screw compare to the linear encoder. The process that we call "screw calibration" maps the differences every 0.01 inch and stores them in the flash memory of our PhSTdrive™. It is an intelligent stepper motor drive (DSP microcontroller based) that allows using servo feedback and/or dynamic real time corrections based on the screw calibration map.
This type of positioning system also shows incredibly high accuracy of less than 8 μm positioning error @ 254 mm (10 inch). It has the advantage that the cost of relatively expensive linear encoders is eliminated and the accuracy is still close to the first one.
We offer models with both positioning systems.
Despite of the type of the positioning system (servo or calibrated screws) we are taking in account all thermal expansion factors, such as screws temperature, encoders temperature and material temperature. All factors related to the material under machining are settable by the operator.
After mapping the screw errors or using servo feedback (depend of the model selected), we have eliminated the main sources of positioning errors and the thermal expansion appear to be the main factor to the final accuracy of the machined product.