totally compatible -- mechanically,
electrically, and in form factor
-- with the previous generation of
the Sigma already on the market,
and 2) to design the new driver’s
printed-circuit board (PCB) for
optimal heat dissipation.
In the previous generation
printer, the stepper driver IC was
a Texas Instruments DRV8825,
commonly used in 3D printers
because of its wide range of
current and voltage ratings.
However, it is very noisy and not very intelligent, as it lacks features such as step
interpolation or motor stall detection.
For its new R17 printer design, BCN3D chose the TMC2130 stepper driver
IC without integrated motion controller because of its 1/16 microstepping with
1/256 interpolation, compared to the previous driver IC’s 1/32 microstepping rate.
This increase in steps using step interpolation makes the motor’s movement much
smoother than other driver ICs can accomplish, without affecting step generation rate.
It also reduces sound dramatically. In addition, sound levels are reduced thanks to the
driver IC’s advanced control of the motor windings current.
Pain Point #2 - Increased Miniaturization
In electronics design, space constraints are always a challenge. Because the
mechanical design of the machine had already been done in the prior generation,
measurements were especially constrained. Also, in this case BCN3D wanted the
smallest PCB possible for its driver module to reduce costs, but also needed enough
space to be able to dissipate the heat that would be generated. Since the TMC2130
integrates a microstepping sequencer and power driver circuit into a single compact
QFN36 package, it was possible to design a PCB that is small enough to be easily
co-located with its companion motor (Figure 2).
Until the R17 product generation, BCN3D had been designing two-layer PCBs for
all of its printers’ driver modules, as well as for the previous Sigma model’s mainboard.
In order to design the new driver module’s board to fit the same form factor as the
previous generation Sigma yet maintain optimal heat dissipation, two additional
layers were needed for main power and ground. Adding these greatly improved heat
dissipation and did not produce any new design challenges.
BCN3D uses only stepper motors in its printer designs, which are integrated
within the structure of the machine. Each axis of the printer is driven by a motor and
a co-located stepper driver module. The motor/controller pairs are connected to the
main control board via flat flexible cables (Figure 3). This integration was chosen to
physically separate the stepper driver modules from the mainboard, which has two
major benefits. If a driver gets damaged, the driver module can simply be changed,
instead of swapping out the mainboard. EMI performance is also improved. The stepper
motor winding cables are the shortest possible, so that emissions from the high-current
motor cables are reduced.
Pain Point #3 - Time-To-Market
The timeline for developing the new stepper motor driver module was around six
months. Since the project was replacing a working driver module with a new one,
there was no need to change the design and engineering process. Although there
were some time-to-market pressures, this was not a new product design.
While the new fan system had virtually no impact on costs, the implementation of
Figure 2. One of the interchangeable stepper motor driver
boards used in the R17 printer. Source: TRINAMIC