Ultrasonic Alignment tool for Bed Leveling+zeroing of stage + Filament monitor

[ShadowX]

"The concept seems very interesting. However, I think it can be a lot more successful and popular with 3D printer users if there is a rigid mount to maintain a fixed position on the print head and the device directly interfaces with the controller card probe interface.”


We considered a tapped M3 hole on the back of alignG. You can simply mount it using a M3 screw and simple mechanical structure. You can even glue it to the surface if you need a permanent attachment.
Remember that there are two very important advantages for alignG when comparing with any dial indicator: (1) dial indicators in the price range of alignG always apply a (spring loaded) force to the surface, roughly about 1 Newton (100 grams). To make sure that the force is not displacing the dial indicator, you need a very rigid mounting for the dial. When speaking about 15-micron displacement, 1 Newton force is huge. (2) a dial indicators in the price range of alignG weights about 100-150 grams. So, you need to consider that in the structure of the mounting fixture. In addition, the weight of mounting structure is often more than the weight of dial indicator, take that in account!
alignG is a non-contact measurement device; so, no worries about the spring-loaded force to displace it. In the other hand, it weighs only 20 grams. A strong magnet tape can simply keep a 20 gram gadget in place for a long time, except if you want to intentionally displace it. For sure, there are many ways to permanently attach a 20grams gadget to your extruder, if you want to install it for one time and leave it there.


“The device should have the option to trigger at some set height above the bed and it should have an output signal that can be directly connected to most 3D printer probe endstops. If it can do that and maintain accurate/repeatable readings, it would be a great contact-less bed leveling tool that can use the automatic bed leveling systems already built into most modern firmware like Marlin, Repetier, DuetWifi, etc. The location of the probe in reference to the tip of the nozzle is critical and must be a fixed distance. Without a rigid mount, the measurements would not be repeatable if the device moved.”


We considered an option for the output port of alignG, providing analog/I2C/USART interface for creative developers to integrate alignG into their system. The precision value reported for alignG (25 micron for alignG-I & alignG-II and 15 microns for alignG-III) are the standard deviation of the measurement. Standard deviation also represents the repeatability of the measurement system. Using alignG, you will have a repeatable reading.
There is no way that somebody compares a 15-micron precision sensor with an IR sensor or inductive proximity sensors, commonly used in the auto bed leveling systems. Even a high precision premium brand inductive sensor still lack the necessary accuracy. Inductive proximity sensors are limited to the conductive (or magnetic) target materials. If you have a glass bed, probably you need a conductive tape on top of that. Proximity sensors are not measuring the distance; So, your measurement is dependent on the accuracy of the Z-Stage. While using alignG, there is no need to move the Z-stage; because it measures the distance. Inductive proximity sensors have a large hysteresis problem, sometimes up to 20% of their sensing range, look at their datasheet. What inductive proximity sensors measure depends on the target material and even its thickness. If you have a thin aluminum bed, the measurement will depend on its thickness uniformity. It is a small dependence; but when talking about micron precision, it is counted.

“I honestly can't forsee myself doing a manual bed level each time I print with a separate software on a device that is attached to a magnet. Watching the video, the locations indicated for each spot is not even clear. Do you randomly pick a spot? The firmware in Repetier can probe over 40+ points on a bed and create a contour profile of the entire surface if needed. It can also do it without user interaction. Some beds are concave or convex and not planar. The leveling software in the video demo assumes the bed would be flat. I run an automatic bed level probing routine each time before I print. The height can change slightly just with temperature deltas between the hot end and the heated bed. Some of the changes can be enough to cause poor or too much adhesion on the first layers.”

Even if you are always using an auto leveling mechanism, it is always recommended to keep your bed leveled. If the miss-leveling in your bed is comparable with the backlash of the Z-stage, auto bed leveling will not result in an excellent finished surface. So, having an instrument that can check the four corners of the bed in few seconds is always useful.

Some of your responses do not make any sense. The response on the force needed on the dial indicator is absolutely ridiculous. The force required is not the problem with metal tool bits. The amount of force will not deform the tool bit. However, if you mean the internal mechanisms inside the indicator may have backlash, that is a different story. Every indicator has its accuracy levels, but the manufacturer states the accuracy on the spec. You still haven't answered how an ultrasonic device can detect the tip of a cutting bit in reference to the tool holder (ie tormach, R8, etc). The z plane is established to the tip of the tool to the top of a raw stock, not the bed on the mill.

Another factor not mentioned is if the sensor has been calibrated against NIST standard instruments to establish your accuracy claims. The problem I see is the angle of the ultrasonic sensor and detector are fixed, therefore, the arc angle varies in relation to the distance from the tip of the sensor to the surface. Is this a linear signal that is returned or is the signal a non-linear curve? If its non-linear, how is it calibrated? At a fixed location or distance? A range of distance to establish enough curve for the profile? Does that accuracy change as a function of distance from the measuring object? What is the distance range where this accuracy claim is spec'd for? Does the ultrasonic detector compensate for humidity, temperature, barometric pressure, etc that defines air density and compensates? This is an important factor since the speed of sound varies in relation to air density. If it doesn't compensate, measurements taken at hot environments with high humidity would not match the results from measurements at cold locations with low humidity. The advantage that IR sensor has is the speed of light is not affected (or the effects are negligible) by these environmental factors. The speed of sound, on the other hand, is definitely affected by the environment.

http://www.migatron.com/high-accuracy-sensor/

The reason I mention this is the RPS-412A high-accuracy ultrasonic sensor compensates for all these parameters and cost over $2000, and yet, they can only claim an accuracy of 50um maximum. I like to see hard concrete accuracy results using established calibrated industry standards before I can accept what is claimed. I know your spec is for "precision" and not "accuracy". I understand the difference, but listing just the "precision" is not enough (repeatability of the measurement). The measurement might be precise in that moment when you measure, but the accuracy could be off. I would get getting different results on hot days vs cold days. Getting repeatable measurements is not good enough to level the bed. The measured distance needs to be accurate (and precise) since I need the sensor to be calibrated against my nozzle tip. I don't want to keep changing my delta z probe height firmware setting depending on the temperature and humidity of my environment. In case you didn't know, the IR sensor is spec'd to 0.01mm (10 um), so its more precise than your device.

https://miscsolutions.wordpress.com/mini-height-sensor-board/

I saw on one of the FAQ that claims the device is accurate to 0.0015 cm (15 um). Yet, the spec for precision is 15um to 25um. That absolutely makes no sense at all. Unless you mean the 15um only applies to the sensor spec'd at 15um and the 25um sensor's accuracy is 25um. Even then, its a stretch to say the accuracy is higher than the precision level for the 25 um. I can't be measuring something accurate to 15um when my measurements itself is varying up to 25um from one measurement to the next without moving the carriage. It just doesn't make any sense. If you said the sensor is precise to 15um, but only accurate to 25um, that is more believable. I hope this is more of an oversight in terms of spec'ing the device properly. A simple temperature cycling test with the device in a controlled chamber cycling between hot and cold (10F to 160F) can easily determine the accuracy claims. If the measurements are within 15um in that condition, then it would prove the accuracy claims.

The autoleveling mechanism is the tool to keep the bed level. Not only is the parameters used to calibrate out the level but adjust for any imperfections of the bed. I don't understand your logic where you have 4 points in the corner (not clearly defied via Gcode) is more accurate than 40 measurements across the bed using precise and repeatable locations defined by the bed leveling algorithms that goes to the same spot every time you level. In terms of checking each time, the process is to first establish the endstop positions using fixed length of rod (in the case of a delta machine). At that point, the system will move the carriage to each point and directly read the Z height value on the computer or LCD screen. You can adjust the endstops as needed if you want a pre-set height. I don't see how your system is any different in terms of process other than a separate computer program to measure the height. You can also take the data from the bed leveling and do a least squares fit to adjust for imperfections of the build such as Delta frame angles, the bed tilt, bed warpage, and so on. The process has to go through several iterations if you want to get the height measurements within a narrow range. These values are automatically fed back to the firmware to control the delta radius, end stop adjustments. Every firmware has differences. I hope you understand this is not just a check four corners and you are ready to go situation.

Adding a analog/I2C/USART interface sounds like a great idea, but why should it be end users or 3rd party developers making tools for it to work on a 3D printer? If you are trying to sell this to 3D printer users, it should already have a pre-defined interface that works with the existing controller boards like Rumba, Duet, and firmware like Marlin, Reprap, Repetier, etc.

I absolutely like the idea of having M3 mounting holes. It would be great for users to mount the sensor in a rigid configuration.

I am not here to crap on your thread. I just want to get reasonable answers so other 3D users are informed.