The CNC machine how to accurately measure coodinate?

Learn the Arduino platform. The flashing led covered, turning the Cam too. Now I want to collect something really useful to quadcopter, I probably have not grown, but the CNC machine (for a start, to draw something) I seem to collect quite capable.


If you collect such — as you count down the coordinates? Need as much precision, and error of the servo is ± 3 degrees can drastically (thought about connecting via a gearbox to reduce the error, but still decided to ask). I read an articlewhere you can connect to the outputs of the digital caliper — that's cool, there's a measurement accuracy of ±0.05 mm — excellent accuracy, but this article (end of 2011) the people also collected the homemade machines: as reckoned coordinates?


But, maybe there is an elegant way of measuring of coordinates? Really interested in the methods used, not daydreaming and speculation (I know).
October 8th 19 at 03:45
4 answers
October 8th 19 at 03:47
Solution
Usually, the actuator is a stepper motor on it and count the coordinates (without feedback)
Plus counting steps.
And in order to determine exactly zero, it is best to use a mechanical stop, for example, to take a drive up to the stop + a "just in case" to do 50 more steps (you do it in many cases, because limit switches often have a hysteresis, which makes the error zero can get very large — up to hundreds of microns). - Timmothy50 commented on October 8th 19 at 03:50
Yes, the use of linear encoders in the "home" is fraught with unnecessary costs. - Timmothy50 commented on October 8th 19 at 03:53
Why? at low speed the most - niko.Nicol commented on October 8th 19 at 03:56
I think the machine does not need a zero at the stop. Failed manually to the edge of the workpiece and this will be zero. And the drawing has been drawn with the edge of the workpiece. And limit switches need more like fuses. - Angelina_Wyman commented on October 8th 19 at 03:59
October 8th 19 at 03:49
Stepper motors actually measure the number of revolutions of the gear, respectively, will error accumulated in the reducer (which is their main source, in addition to looseness of the joints and deformation of the whole structure under physical stress, inertia, self weight and temperature changes).

So it is necessary to measure the angle of rotation of the last joint in the gearbox (or the penultimate, then it is possible to combine the measurement of the angle with the number of revolutions) or even the distance that moves the tool itself.

To change the angle it is easier to use a disk with lots of cuts from glass/cracks have opaque/just strips and to consider them the usual photocell (pair to determine the direction of rotation). Now look, Wikipedia has a reasonable article about the encoders: ru.wikipedia.org/wiki/Датчик_угла_поворота

If we are talking about 'DIY' and low budgets, in this case, the larger the radius of the disk, the easier it is to make yourself, even stripes can be printed on the printer. It is also possible to develop the idea, and instead drive and fotoelemente can put a mirror/flashlight and catch the light Bunny webcam bonLichem distance — it is not getting coordinates in real time, and about the constant automatic compensation of measurement errors (yet this light rabbit will be recognized....)
Where the reducer will accumulate errors? Teeth slip, or what? - Timmothy50 commented on October 8th 19 at 03:52
Reducer complex device, looseness of joints, gears and most importantly, the gap between the teeth of adjacent rings (and they will always be creating a pause when changing direction of rotation) - Timmothy50 commented on October 8th 19 at 03:55
But this error will not accumulate. You can even try to take it into account when changing the direction of rotation. - niko.Nicol commented on October 8th 19 at 03:58
October 8th 19 at 03:51
If you use a stepper motor, it is necessary to use the encoder(there are a lot of options, the easiest strip on the tape and ready a pair of led phototransistor), a gearbox with a high gear ratio and a fairly fancy control algorithm for the engine speed to precisely positioned.

In self-assembled machines are usually used all the same stepper motors that are much simpler, sometimes do feedback do not involve winding of the stepper motor to catch potential omissions of steps, or again use the encoder.
October 8th 19 at 03:53
I should add that even should look at the software, which intend to run the machine — some are not able feedback. And then only to stepper engines and no feedback. Yes, even under heavy load sehovici able to skip the steps and then the error accumulates.

It makes sense to adjust the current roughly 30% more than you start to skip steps when the biggest load on the machine.
If the software and there is no feedback that bothers to implement it at the controller side? - Timmothy50 commented on October 8th 19 at 03:56

Find more questions by tags Microcontrollers