Adding super-accurate LVDT based position feedback for sled position.
I’d like to get forum member input on adding an LVDT position sensor (or two) to reduce a lot of the calculation load off the Arduino controller(=higher speeds and room for more features) and at the same time provide a huge leap in sled position accuracy.
If you are new to LVDTs here is a brief tutorial:
I’ve read how it works but I’m unclear how it would be implemented. What scale would you use? they say they are up to + - 30 inches. Can you show this in a drawing?
Thank you
I like the idea, but also am having difficulty understanding how it could be implemented on the scale of a typical Maslow.
Also, I see this being used one of two ways. First, it could be used to form a closed-loop position feedback system for the sled position, as you mentioned. But alternatively, it could be used in a temporary manner to characterize the absolute accuracy of the current algorithm across the workspace, and help guide us as to which future accuracy improvements would be most beneficial as well.
<devil’s advocate> The encoders give us better resolution, even with a larger sprocket. Two full-on LVDT setups would cost more that the Maslow. </devil’s advocate>
If the goal is to offload position detection, putting a microP between each encoder and the Arduino to count pulses and report when polled could be much cheaper and be incorporated on the PowerControl board. Google quadrature decoded ATtiny.
Not sure about cost (meaning I didn’t look into it yet), but I was thinking since LVDT resolution is so high, we could attach a retractable wire to the sled and then gear it somehow to scale the sled’s motion over ~8ft to the ~12in stroke of the LVDT.
…Do you have representative costs of just the LVDT?
Not many sites with prices, a bad sign for price. Here is an 8" unit for $385. Note these will need high-resolution A/D conversion to reach the highest accuracy.
This was an idea I was interested in pursuing when I receive my Maslow, but I do think the costs of building such functionality into the standard Maslow would be difficult. Sensor readings of +/- 0.4mm over a 4x8 ft area is likely to be over $100 or so, which would begin to make a serious dent in the price.
Having said that, an option to add the sensor kit on for an additional cost to yield improved accuracy is a great idea I think.
Additionally, I think it would be extremely useful if a couple people built such kits onto their Maslows and then tried to characterize the next steps of the kinematics to improve the algorithms. I would be willing to build such an addition to my Maslow, but do not know the best way to do this.
This:
My understanding is that the goal for Maslow is to keep the price down and improve accuracy, in that order. If that is the case, I think the solution has to be largely software based. This is entirely based on my intuition though and I would love to be proven wrong.
Another option could be to have a tiered product offering? Maybe some type of accuracy add-on, similar to the z-axis.