In our last post, we showed that you can get more torque at higher speeds if you operate a motor at a higher voltage. In the example below, the red curve, measured at 70 VDC, provides much better high speed torque than the orange (12V) curve. So why not always use 70 volts? Better still, why not apply 100 volts and really flatten out that curve?
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In our post What Do NEMA Sizes Mean?, we examined the NEMA frame sizes in which step motors are made. Larger frame sizes produce more torque. But this is not a one dimensional process: within a given frame size, the motor length can vary and that also affects torque. Because step motors require expensive tooling in order to be produced economically, a fixed rotor length is chosen, as is the stator that surrounds it.
In our last post, we explored the possibility of connecting a step motor to a small gas engine for use in recharging a 12 volt battery. The effort resulted in a computer model which we hoped to use to optimize the design without having to expend excessive time and effort on trial and error. Our first concern was whether the step motor had the optimal number of winding turns on the stator. Changing the winding of a step motor is a difficult experiment because of the complexity of reprogramming a winding machine and loading it with a different size wire.
Background In some applications, power dissipation in step motors and drives is a critical aspect of system design. Too much heat from the drive can cause a cabinet to overheat. Too much power loss in the motor can cause the motor to overheat at high ambient temperatures. Heat can also transfer into attached equipment causing it to misbehave. One example is a digital ink pump, where excess heat from the motor can cause undesirable changes in the viscosity of the ink. A recent customer was modeling their enclosure and requested detailed power dissipation data.
Step motors are prized for their ability to provide precise positioning without a feedback mechanism or closed loop control system. This inherent precision is owed to the fact that hybrid step motors have toothed rotors and stator that create an electromechanical gearing system to increase the resolution provided by rotating the stator field by 50X. Move the field by 90° (one full step) and the motor shaft moves by just 1.8°.
In our last post, we learned about step motor holding torque and pullout torque when full stepping. There was a time when full stepping was the only affordable way to drive a step motor, but advances in processing and sensing have made it possible to divide the typical hybrid step motors 1.8 degree full steps into much smaller steps. Why would we want to do that? Smaller steps improve smoothness and accuracy. Let's revisit the torque versus displacement curves of a step motor being driven in full step. Holding torque and pullout torque are noted.
(The OSI Model, Part 1 may be found here.) Welcome back! Last time we covered the basics of the OSI model and briefly discussed two of the most common forms of serial communications: RS-232 and RS-485. This time we'll take a quick look at TCP/IP and conclude with a look at how something like standard snail mail might look if we press-fit it into an OSI model mold.
Applied Motion Products stepper and servo drives have supported sensorless homing for several years. Also known as “hard-stop homing”, there is no need for a hard-wired home sensor (hence the name sensorless) when using this method because a physical hard stop is being used to stall the motor, create a position following error, then automatically recover from the fault by moving off the hard stop and setting the home position.