Microstepper Driver
Apr 17, 2014 Hi, A small video showing my step motor controller. Based on L297 L298N. Here is a link to download the PCB DipTrace : https://drive.google.com/file/d.
KSTEP is a KFLOP expansion board designed specifically for plug-and-play stepper motor control. With only a motor
power supply, stepper motors and the KFLOP KSTEP you have all you need to start controlling 4 motors or 8 with 2 KSTEPs.
This ease-of-use also comes with high performance, high efficiency, and additional 12-24V isolated I/O expansion sufficent
for most applications. Although it is possible to use third-party stepper or servo drives with our KFLOP
controller, KSTEP provides complete connectivity with a single ribbon cable connection,
easily mounts to KFLOP with standoffs, and gets the most out of our software. In addition, KSTEP s ultra low resistance MOSFETS
eliminates the need for special cooling and heat sinking. This setup reduces cabling and wiring and puts everything you
need into a nice footprint. KSTEP really is a culmination of many customer requirements in one expansion board.
199 USD Plus Tax, S H
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The lure of Microstepping a two-phase stepper motor is compelling. Visions of Microstepping a 1.8-degree hybrid stepper motor with 256 microsteps per full step flash in your mind. The resolution of 51,200 microsteps per revolution entices you. You re glad you don t own stock in high-resolution encoder companies.
Where s the catch.
The real compromise is that as you increase the number of microsteps per full step the INCREMENTAL torque per microstep drops off drastically. Resolution increases but accuracy will actually suffer.
Few, if any, stepper motors have a pure sinusoidal torque vs. shaft position and all have higher order harmonics that in fact distort the curve and affect accuracy. And while microstepping drives have come a long way too, they still only approximate a true sine wave.
Significant too is that any load torque will result in a magnetic backlash, displacing the rotor from the intended position until sufficient torque is generated.
The actual expression for incremental torque for a single microstep is:
1. TINC THFS x sin 90/µPFS
The incremental torque for N microsteps is:
2. TN THFS x sin 90 x N /µPFS
Where:
SYMBOLS and UNITS
Symbol
Definition
Unit s
µPFS
Number of Microsteps per Full Step
Integer
N
Number of Microsteps taken
N Less than or equal to µPFS
THFS
Holding Torque - Full Step
oz-in
TINC
Incremental Torque per Microstep
TN
Incremental Torque for N Microsteps
Table 1 dramatically quantifies the significant impact of the incremental torque per microstep as a function of the number of microsteps per full step.
A full step is considered 1 microstep per full step for Equations 1 and 2. A half step is 2 microsteps per full step.
Microsteps/full step
Holding Torque/Microstep
1
100.00
2
70.71
4
38.27
8
19.51
16
9.80
32
4.91
64
2.45
128
1.23
256
0.61
As the Number of Microsteps per Full Step Increase
Table 1
Incremental Torque per Microstep Full Step
The consequence is that if the load torque plus the motor s friction and detent torque is greater than the incremental torque of a microstep successive microsteps will have to be realized until the accumulated torque exceeds the load torque plus the motor s friction and detent torque.
Simply stated, taking a microstep does not mean the motor will actually move. And if reversing direction is desired a whopping number of microsteps may be needed before movement occurs. That s because the motor shaft torque must be decremented from whatever positive value it has to a negative value that will have sufficient torque to cause motion in the negative direction.
Accuracy vs. Resolution
What if the motor is not loaded. you ask. Thinking of using microstepping for some type of pointing or inertial positioning.
Well, the stepper motor still has friction torque due to its bearings and it has a detent torque, in addition to other harmonic distortions. You ll have to wind up enough incremental torque to overcome the bearing friction. Even more disruptive than the bearing friction is the detent torque, which is typically 5 to 20 of the holding torque. Sometimes the detent torque is adding to the overall torque generation, sometimes it is subtracting from the powered torque generation. In any case it wrecks havoc with your overall accuracy.
Indeed, some manufacturers fabricate microstepping versions of their motors. Their efforts typically are to reduce the detent torque, usually at the expense of holding torque, to make the torque vs. rotor position closer to a sine wave, and to improve linearity of torque vs. current. These efforts reduce, but do not eliminate the compromises associated with microstepping in regards to accuracy.
How about using a lookup table to correct for the inaccuracies in the motor and microstepping drive. That too has been utilized. The problem is that if the load torque changes from when the lookup table was made the results can be worse than if you had not utilized a calibrated table at all.
Why Microstep Then.
There are still compelling reasons other than high resolution for microstepping. They include:
Reduced Mechanical Noise.
Gentler Actuation Mechanically
Reduces Resonances Problems
In summary, although Microstepping gives the designer more resolution, improved accuracy is not realized. Reduction in mechanical and electromagnetically induced noise is, however, a real benefit. The mechanical transmission of torque will also be much gentler as will a reduction in resonance problems. This gives better confidence in maintaining synchronization of the open loop system and less wear and tear on the mechanical transmission system.
In fact, taking an infinite number of microsteps per full step results in two-phase synchronous permanent magnet ac motor operation, with speed a function of the frequency of the ac power supply. The rotor will lag behind the rotating magnetic field until sufficient torque is generated to accommodate the load.
Oct 17, 2013 See Connecting Easy Driver to a L298N bipolar stepper driver board to boost.
EAS Microstep is our single axis microstepping chopper driver board for stepper motors. It is based on the National Semiconductor LMD18245 3amp 55volt full bridge.
In dual phase mode, also known as two-phase on, full step excitation, the motor is operated with both phases energized at the same time.
KSTEP 4-Axis Microstepper Amplifier for KFLOP KSTEP is a KFLOP expansion board designed specifically for plug-and-play stepper motor control. With only a motor power.
Dynomotion Motion Control Boards for CNC Manufacturing and Robotics Applications
