垃圾房
DRIVER & CONTROLLER FOR STEPPER MOTORS
Programmable Adaptive Microstep Table
Table of contents
1 Microstepping (1)
1.1 Motor Dependence (1)
1.2 Simple Approach for Microstep Wave Optimization (2)
2 Programming the Incremental Microstep Table (5)
2.1 Incremental encoding (5)
3 Revision History (7)
3.1 Document Revision (7)
1 Microstepping
While stepper motors classically have been operated in audible and tangible (half- and full-) steps, they have been loud and prone to resonance failure. The first aim of introducing microstepping is the reduction of resonance and operation noi. The cond benefit of microstepping is the drastically improved position resolution. In many aspects, a sine wave is a good solution for reaching a good mi
crostepping: a sine wave and a cosine wave cau a constant power dissipation in the motor, so the motor can be operated at its maximum thermally limited power, independently of the position within the waves. Many stepper motors work well with sine wave drive.
How to find the best waveform for a given motor? Normally, there is no specific data available for the stepper motor ries. A motor might be optimized for best microstepping or for highest torque, or for a certain form factor or tooling. The waveform can be best optimized when using a high resolution encoder or a lar pointer attached to your motor and moving the motor at very low velocity.
The aims of the optimization are:
冠军溜冰场∙ Even distribution of microsteps, giving a constant velocity at slow speeds
∙ Constant torque independent of position.
1.1 Motor Dependence
As a first step, you should understand which parameters have a direct or indirect influence on the microstep performance.
Table 1 Parameters which should be considered
1.2Simple Approach for Microstep Wave Optimization
We will optimize the microstep wave table for equidistant microstepping using a simple interactive approach which does not require expensive measuring equipment and does not need in-depth data of motor physics. This approach does not consider torque variation of the motor, it just compress a
nd drags the sine wave to yield an evenly distribution of microsteps. In a next step, the amplitude can be optimized in order to give a constant torque independently of the position.
Take your motor into operation at nominal conditions. In ca your appliance does not directly allow asssment of the microstepping equidistance, you can attach a needle to the axis. A very good means is a tiny lar pointer, becau of the optical amplification to a near wall. If available, a high resolution encoder can be ud even for automatic tuning of the microstep wave.
1.Be sure to first tune the chopper parameters and motor current tting. Bring the motor into very
slow rotation, e.g. a few microsteps per cond. Check the quality of the microstepping using the needle or the lar pointer. You will probably e deviations from the optimum, equidistant stepping. Start with a sine wave.
2.If you u a lar pointer pointing to a distant wall, attach a scale to the wall. You can design the
scale in a way, that it divides the distance of two fullsteps into a number of equidistant steps.
Position the first fullstep corresponding to the 0° position at table position 0, and the next fullstep to the 90° position at table position 256. You do not need to u each microstep position in between for
checking in ca you work with high resolutions like 256 microsteps. A good result will already be achieved when you optimize the positions for 8 or 16 evenly distributed microstep positions and later on evenly distribute the remaining microsteps in between. The first and last positions are fixed to the original values at 0° and 90°, as they mark the original fullstep borders. You can do the same using a high resolution encoder.
3.Now position the motor as exactly as possible to each of the equidistant steps (P1, P2, …) using
the highest available microstep resolution, e.g. 256 microsteps. Take into account, that motor friction might influence the exact positioning and multiple trials will help reducing errors caud by friction. Take a note of the microstep pointer (MSCNT) for best position match for each position (shift each position as required).新年的诗词
4.Now you have a lookup-table (shifted positions for blue trace in Figure 1.2) which allows exact
positioning to the determined values. The sine values at the noted MSCNT positions, which are
required to exactly reach the desired microstep positions, are the optimized entries for the microstep positions. You can do an interpolation between each two entries to extend the microstep c
urve to the original table resolution, e.g. to 256 microsteps. For this task a spread-sheet may be helpful.
Figure 1.1 Tuning the motor position using a lar pointer
y
256
248
Figure 1.2 Modifying the wave for evenly distributed microsteps (example)
After optimizing the positions, an optimization of the torque can be done. This will help the motor to keep equidistant positions when it is loaded with a certain torque. This optimization step will require more measuring equipment and can best be realized in an automatic tup. An encoder coupled to the motor can be ud for torque measurement by superimposing a step (e.g. 90° electrical angle) on the motor and measuring the instant acceleration of the motor.
[Hier ein Bild eines Motors mit Encoder dran und Mas und einem Winkelschritt in der Ansteuerung] Like the positions have been compresd and dragged in the previous step (horizontal arrows in Figure 1.2) now the amplitudes become scaled in the same way (vertical arrows in Figure 1.3). While scaling the wave, keep in mind that the drivers optimally work when sustaining the peak amplitude at the maximum permissible level (248). A cond iteration of both steps might still give improvements, as there is a small dependence of the position from the absolute current level, due to the motors’ residual torque.
256
248
Figure 1.3 Modifying the wave for constant torque (example)
2 Programming the Incremental Microstep Table
To understand the background of the incremental coding of the microstep table it is good to have an idea of the characteristics of the microstep wave.
北欧三国A microstep table for a two pha motor has certain characteristics:
1. It is in principle a rever characteristic of the motor pole behavior.
2. It is a smoothened wave to provide a smooth motor behavior. There are no jumps within the
wave
3. The pha shift between both phas is exactly 90°, becau this is the optimum angle of the
poles within the motor.
4. The zero transition is at 0°. The curve is symmetrical within each quadrant (like a sinewave).
百度英语
5. But it must not be strictly monotonic as the example in the previous chapter shows.
Due to the special characteristics, the wave can be described by one quarter period and there is only a certain change possible between two adjacent positions. Following 4, the slope of the wave is normally positive, but due to torque variations it can also be (slightly) negative. Considering the facts, it becomes clear that the wave table can be compresd. The incremental coding ud in the TRINAMIC ICs us a format which reduces the required information per entry of the 8 bit by 256 entry wave table to slightly more than a single bit.
2.1 Incremental encoding
The principle of incremental encoding just stores the difference between the actual and the next table entry. To have an absolute start value, the first entry is directly stored (START_SIN). For the ea of u, also the first entry of the shifted table for the cond motor pha is stored (START_SIN_90_120). Using a single bit per table entry would allow any inclination between 0 and 1. E.g. a 0-bit could mean “do not add anything” and a 1-bit coul d mean “add one”. This would allow describing a digital slope of 0° (all bits zero) to 45° (all bits one). It quickly becomes clear, that higher inclinations are necessary. However, the inclination will not drastically change from point to point. Therefore, the wave can be divided into a number of gments with different ba inclinations. Using a ba inclination of one, a 0 bit would mean “add one” and a 1 bit would mean “add two”. This way, a slope between 45° (all bits zero) and 77.5° is yielded (all bits one). The TMC drivers u four inclination gments (0, 1, 2, 3) with the ba inclinations (W0, W1, W2, W3) and the gment borders (0, X1, X2, X3, 255). The ba inclinations can be t between -1 (falling slope) and +2. This way, slopes between -45° and 78.75° can be described. The default sine wave table in the drivers us one gment with a ba inclination of 1 and one gment with a ba inclination of 0.
y石婆婆
256
神州五号
+2/+3+1/+2+0/+1-1/+00
Segment
名人名言大全100000句inclination W Figure 2.1 Wave showing gments with all possible ba inclinations (highest inclination first)
