TMC424-PI24 Trinamic Microchips, TMC424-PI24 Datasheet - Page 41

• Manufacturer Part Number: TMC424-PI24
• Description: Economic Miniature Three Axis Microstepping Stepper Motor Controller
• Manufacturer: Trinamic Microchips

TMC428 DATASHEET (V. 2.00 / November 12, 2003)
12.3 Microstep Enhancement
Even for stepper motors optimized for sine-cosine control, it is possible to improve microstep behavior
by adapting the microstep look-up table (LUT). For different types of stepper motors, a periodic
trapezoidal or triangular function similar to a sine function or a superposition of these function as a
replacement of the pure sine wave function (Figure 12-1) might be a better choice. Taking the physics
of stepper motors into account, the choice of the function for microstepping can be determined by a
single shape parameter σ as explained below. The programmability of the microstep look-up table
provides a simple and effective facility to enhance microstepping for a given type of two-phase stepper
motor. Enhanced microstepping requires accurate current control. So, stepper motor driver chips with
enabled and well tuned fast decay (resp. mixed decay) operational mode are need to be used, e.g.
TRINAMICs smart power TMC236 / TMC239 / TMC246 / TMC249 drivers.
Non-linearity resulting from magnetic field configuration determined by shapes of pole shoes,
ferromagnetic characteristics, and other stepper motor characteristics effect non-linearity in microstep
behavior of real stepper motors. The non-linearity of microstepping causes microstep positioning
displacements, vibrations and noise, which can be reduced dramatically with an adapted microstep
table. The best fitting microstep table can be determined by measuring the microstep motor behavior,
e.g. using a laser pointer based on the sine-cosine microstepping table.
Nevertheless sine-cosine microstepping is a good first order approach for microstepping. The
microstep enhancement possible with the TMC428 is based on replacement of the look-up table
initialization function sin( ) used for sine-cosine microstepping by a function with the shape parameter
σ. A quarter sine wave period is the basic approach for initialization of the microstep look-up-table . A
quarter of a trapezoidal function or a quarter of a triangular function is chosen depending on the shape
parameter σ for a given stepper motor type.
The look-up table (f( ) ) of the TMC428 enfolds a quarter period (0 ≤
is expanded to a full period (0 ≤
added automatically by the TMC428 during operation. So, to reach function value (f( )), one
automatically gets a pair of function values {f(
automatic expansion of the TMC428– primary provided for sine cosine microstepping (f( ) = sin( )) –
also works fine with other microstep wave forms f
Figure 12-1: Microstep enhancemant by introduction of a shape function f
Copyright © 2000–2003 TRINAMIC Microchips GmbH
1
2
1
f
0
2
( f
0
)
(
up to 64 micro steps
1 full step
)
4
1

 




f
f
2
circle
f
box
circle
_
_
circle
r
hom
3
4
(
(
b
)
(
)
)
for
for
for
< 2 ) and the phase shifted companion function value (f( -
0
0
0
σ
.
); f(
with
-
2
/2 )} respectively {sin(
1
0 .
<
/2) only. This quarter period
box
y
1
σ
( )
0 .
and
); cos(
0
)}. This
/2 )) is
x
41
2
.