ClearPath Integrated Servo Motor: Pulse Burst Positioning Mode

[@Arduinorollo]

Nice Demo. I wonder how you did the smaller velocity on the last move in the first example. Via longer pulse width perhaps. Very intriguing mode especially combined with RAS!

[@TeknicInc]

Hi Felix, Thanks for the positive feedback! The Pulse Burst Positioning mode has two user-settable velocities. In MSP there is an option called Alternative Speed Limit. (You can see this field in the MSP screen shot from 1:33 to 1:44 of the video) You set this value to a second desired speed limit and trigger this alternative speed as needed. In the first demo of this video, the alternative speed limit is used in the final move. While the alternative speed limit is not discussed in the video, this is covered in the Pulse Burst Positioning section in the ClearPath manuals. Best regards, Erik M.

[@PicoGirl]

I still haven't seen any positional feedback in the operational modes of these motors. So I don't think these motors have the capability that I need. What about your other motors? Or maybe, can the timing of this mode be calculated somehow to know the precise mathematical waveform of the ramp up and ramp down between any distance (including low jerk)? We need to be able to pulse a laser at very precise distance based intervals while ramping up, at maximum speed, and ramping down.

[@TeknicInc]

Hi PicoKit, Thank you for taking the time to reach out and comment. I realize in advance that my response here is going to be a little long - but I want to answer your questions, and discuss the differences between the three ClearPath motor series (more on that in a second). *Feedback* : All of the ClearPath servos (regardless of series) are closed-loop servos and can provide feedback to the outside world. The ClearPath SD and MC series servos in particular have a dedicated, user-configurable output bit (our documentation refers to this as the “High-Level Feedback” or HLFB for short). HLFB can be configured to verify that the servo is tracking your command within a user-defined position tolerance. You can read more about this HLFB output in our User Manuals found here on our website: www.teknic.com/downloads/ When working on an application where you need to control the motor’s position, speed, and acceleration, (and infinitely vary all three to follow an arbitrary path through space or cut a specific part), you will want to use the ClearPath SD series of motors (not the ClearPath MC that we demonstrate in this video). When using the SD motors, your Step and Direction controller will be able to trigger a device (such as a laser) off of the step command and get excellent accuracy (we’ve had customers do this in the past). You’ll find the operational mode video for the ClearPath SD motors here: www.teknic.com/watch-video/?id=1#OpMode11 *ClearPath Series Overview* : As I mentioned before, there are actually three different series of ClearPath motors (the MC, SD, and SC), and each has their place in different applications. If you would prefer to jump to an in-depth comparison of the three, please take a look at Teknic’s website: www.teknic.com/products/clearpath-brushless-dc-servo-motors/clearpath-servos/ *MC Series* : At a high level, customers should use a ClearPath MC motor when they want to control either the motor’s position, or the motor’s velocity, or the motor’s torque (but not all three simultaneously). As an example, in the video above we show how you can use a ClearPath MC motor in Pulse Burst Positioning mode to infinitely vary your motor’s position (but all moves are subject to a fixed acceleration limit and one of two velocity limits). *SD Series* : Most CNC customers on the other hand (or any customer who needs to infinitely vary the position _and_ velocity) should use the ClearPath SD series. With the ClearPath SD series you use an external motion controller to create any path through space that you want your motors to follow. Your controller transmits this motion profile to the ClearPath SD motors via standard Step and Direction signals (alternately you could use A/B Quadrature signals to achieve the same outcome). *SC Series* : Customers who want to use Teknic’s C++ or C# class libraries to communicate with the motors from a dedicated host PC (running Windows or Linux) will use the ClearPath SC product. The SC (or software controlled) products are primarily used in applications which require point to point motion. Some customers might be able to use the SC servos in a CNC environment, but doing that is beyond the scope of this response - please contact us directly if you’re interested in doing that. I noticed that you also asked a few questions on some of Teknic’s other videos. Please feel welcome to email us or give us a call for more detailed recommendations for your specific machine. Best regards, Aaron B. - Teknic Servo Systems Engineer

[@Austin1990]

Is there a way to clear the queued pulses and halt the motor? Imagine a platform that the ClearPath motor is moving activates a limit switch, but the micro-controller has already sent six more inches worth of pulses to the motor. The micro-controller would need some way to halt the motor to prevent over-travel. Lastly, the manual says the following: _"The frequency of the pulse train applied to Input B must always be higher than the specified speed limit(s). This ensures that the motor's pulse buffer is never empty. ..."_ If I send a slower PWM signal to the motor, I would expect it to move at a fixed velocity below the specified maximum speed. I imagine that each pulse would be an individual move command. Then, the motor would string these commands together in a seemingly smooth motion. Would it actually function this way? I would like to use the pulse burst positioning mode to position something absolutely along the travel path and also to manually move the position at a slow, steady velocity. Thank you.

[@TeknicInc]

Thanks for your question Austin. In Pulse Burst Positioning mode, once a move has been initiated (via a burst of pulses sent to the appropriate ClearPath input) there is no built-in way to stop or cancel the move. The motor will spin until the move is completed (unless the motor somehow becomes disabled, loses power, or experiences a safety shutdown). This mode was specifically designed to reduce complexity and cost for the user. You also asked a few questions related to pulse burst frequency and motor speed. The thing to remember here is that the ClearPath setup software automatically calculates and displays the minimum frequency at which you must send pulses to guarantee continuous motion. This is called the Burst Frequency Spec in the MSP UI; it is based on your 2 speed settings and your Input Resolution setting. If you send, let's say 800 pulses at a frequency much lower than the Burst Frequency Spec, you will still move 800 increments, but not necessarily in a single, uninterrupted move (it will likely be a series of a few short moves). Here's another way to think of it: As long as the complete set of pulses for Move A is received by the motor before the deceleration segment of Move A begins, you will have a single, uninterrupted move. On the other hand, any pulses received after the decel segment of Move A begins will be buffered in the motor and considered part of Move B (which will execute as soon as Move A completes). Regarding your last comment, in Pulse Burst mode you have only 2 speeds to work with, so if that is not a limiting factor for your application, then the objectives you mentioned should be achievable. If you have any other questions please feel free to contact us directly at [e-mail]. Thanks, Jim W.

[@Austin1990]

Teknic Inc What would happen if I set the "enable" input to low for a sufficient period of time? Would that stop the motor? Moreover, how long must the "enable" input be low to un-enable the motor rather than engage the alternate speed? I did not see this detail in the manual. I will probably need to play with the motor to see how the motor would appear moving through small, discrete steps like that. The $310 price tag is impressive for such an advanced controller being built in. I think that modifying my application (if needed) to accomodate the operations of this motor will be worth the benefits of the effortless control.

[@TeknicInc]

Hi Austin P. De-asserting the Enable Input will definitely cause the motor to stop, but there are some details to consider. First, there are 3 "stop methods" to choose from when you disable the motor: 1) Dynamic Brake, 2) Decelerate to Stop, or 3) Coast. There's a screen shot in the manual that explains these options in greater detail. To read more, open your pdf copy of the ClearPath manual and search on "Actions on Disable/Enable" and you'll be able to check out the available settings. Next. The length of time between de-asserting the Enable input, and the point at which the motor is actually disabled, also depends on a few things. The actual disable time is related to the Alternate Speed trigger pulse width as follows: Trigger Pulse Width Disable Delay 1-3ms 10ms 4-340 ms 3x the setting 341-400 ms 1000 ms Max Trigger Pulse Width setting is 400 ms. Also, if you chose Decelerate to Stop, you' d have to add the time it took to decelerate to a full stop (because you'd still be enabled during the powered deceleration). The exact time to decelerate would depend on your velocity and deceleration rate at the time of the disable event. Note: If you chose Coast or Dynamic Brake as your stopping method you would not have to add extra time. Just keep in mind that we're talking about the time to disable, and not the time at which the motor stops moving. You mentioned limit switches previously, so I wanted to bring up one cautionary point. If you wire a limit switch in series with the Enable input such that a hit on the limit switch opens the Enable circuit (i.e. disables the motor) the motor will be stuck wherever it ends up (until it is enabled again). Regards, Jim W.