I’ve been searching for years but I can’t find a stepper motor encoder (just the encoder) for less than an arm and a leg. Is this technology a secret or something?
What do you mean by a stepper encoder? Steppers don’t use encoders. Are you taking about rotary encoders? Us digital have a good selection. Sparkfun have a few rotary encoders that don’t cost the earth.
I’ve used one of these on a motor before.
@ Sprigo - Ok, colour me impressed.
@ Sprigo - Do these produce 1 pulse per full step of a 200 step stepper motor? I need this to close the feedback loop on a stepper motor and I need the pulses to know that the rotor has reached the correct position before moving to the next step. The system is supposed to respond to varying torque situations. The µC also need to monitor the RPM to instruct the driver (L6470) to increase power.
@ Mr. John Smith - The spec sheet lists a 200 pulse per revolution setting, not sure what your RPM rate you need or what your mechanical load is but we typically use micro-stepping and an appropriate multiple of 200 pulses from the shaft encoders. Comparing the number of step pulses sent to the motor and the feedback count from the shaft encoder in software will likely limit your RPM rate, we use a FPGA to count the pulses and allow for count differences as the motor is accelerated or decelerated, we achieved step rates of about 10,000 p/s.
I am very interested in giving this type of shaft encoder a try as well. I also want to evaluate the L6470 controller in our application.
@ Mr. John Smith - Maybe we can convince GHI to make the Stepper L6470 Module again as it has worked nicely here https://www.ghielectronics.com/catalog/product/418
@ PHITEK - I’ve been able to drive the L6470 successfully using a home made optical encoder solution. The photo interrupter died I think due to ESD but it was working (sorta). I believe inaccuracies in my drilling of the center hole on the polycarbonate substrate causes variations durations of the pulses. The CerbBee is used to setup the L6470.
Given the problems with my home made solution I want to try this new capacitive encoder as well to see how well it works out. I noticed that it is limited to 8,000 RPM (which at 200 pulses per revolution should be a 26.6Khz square wave). I had wanted to achieve that and more, from a NEMA23 motor so that I have enough torque for my application, however I’ll upgrade to a NEMA34 if the torque is insufficient. The L6470 can drive packages that large, just need to upgrade to the POWERSO-36 and use a clip on heat sink.
When I purchase it and test it, I’ll post the result.
EDIT: Here is a picture
@ Duke Nukem - Nah, Gus is more focused on the µC as his niche. No point in competing head on with SparkFun, Adafruit and SeeedStudio. Also, GHI’s version of the driver doesn’t have the SW pin broken out; so no limit switches!
@ Mr. John Smith - The L6470 specs lists a max of 15610 step/s or 4683 RPM @ 200 PPR so the well below the Modular Incremental encoder limit. If I am reading the spec sheet right is has two RPM limits depending on the PPR selected so for 200 resolution it lists 15,000 RPM.
Good to know about the SW pin, I have several GHI stepper modules, to prototype with but will integrate with a USB client controller to operate from our PC based controller.
I don’t have any experience running at 200 PPR, but at the 800 PPR we did a lot of work to “tune” the acceleration / deceleration curves for our worst case load, possibly the L6470 does much of this for you, so again no experience with that controller yet.
@ PHITEK - That 15610 step/s is a limitation of the internal logic. The external step clock is independent of that. It can potentially exceed that 4683 RPM. The L6470 is based on a 2 patents : the Voltage mode driving technology and the ability to calculate the acc and decc steps in real time using an internal µC. I think that both of these patents are controlled by ST Micro.
@ Mr. John Smith - That is very interesting to know there is an external mode of operation.
May I ask if you have tried the sensorless stall detection? This is what has me the most interested in the L6470 controller.
Sadly in North America Digikey does not carry the AMT10 series of devices.
@ PHITEK - I have tried the sensor less stall however not to any extent. I just keep my motor power and speed within reason.
EDIT: Mouser carries the AMT10 and 11 series
There is also another way to change the harmonic of a stepper motor to mitigate stalling called a harmonic balancer. I want to use those in my application as well to prevent stalling.
@ Mr. John Smith - Thanks for sharing the harmonic balancer approach.
Good luck with your project, I hoping to get back to my stepper motor controller evaluation work as well.