dimensions: noise, precision, accuracy, efficiency, and dynamic
behavior. In 3D printing, key considerations are reducing noise,
precision of printing mechanisms, accurate synchronization of
multiple axes for high speeds, and the utilization of closed-loop
motor control and servo control for increasing printing speed
Stepper motors are often used for precise positioning in
applications such as CNC machines and most desktop and
“prosumer” 3D printers. Although favored for their high reliability
and low cost, their downside has been high noise levels, even
at low speeds or at rest. Since printers and desktop devices
are often placed on or near the commercial user’s desk,
that noise can be disruptive, especially during print jobs that
sometimes last many hours.
With modern control processes and careful layout,
these motors can operate virtually silently. Up to now, the
primary source of noise has been the motors’ suboptimal
commutation modes, which lead to vibrations and resonance
of the mechanics for positioning print heads and the extruder
motor. The best way to reduce acoustic emissions is to
reduce resonance and mechanical vibrations by increasing
step resolution using smart drivers. Smaller steps, called
“microstepping,” smooth motor operations, greatly reducing
resonance, and can also increasing printer speed.
Using closed-loop encoder feedback, the actual positions
of the motors can be compared with their commanded target
position and differences logged. Without closed-loop the part
might actually meet the spec precisely but there is no proof,
and precision levels can’t be guaranteed.
In addition, encoder feedback can be used for servo control
of the motors using field-oriented control (FOC) algorithms.
These algorithms typically require some computation effort:
feedback and analog sampling, proportional-integral-derivative
(PID) control loops, matrix transformations, and pulse-width
modulation (PWM) generation. They also have real-time
constraints that make them perfect candidates for being
implemented in hardware, inside smart drivers or dedicated
servo controller ICs. FOC’s benefit is improved motor efficiency
as well as step loss prevention.
Closed-loop motor control and servo control can also be
used to increase both printing speed and precision of desktop
Motion control in its many aspects has been around for a
long time. But what is new now? What will the future bring?
Here are some future trends:
Motion control will become a building block - In networked
systems and environments, terms like “Io T” or “inputs and
outputs” now dominate, and interfaces dominate. Because of
this, engineers’ thinking is becoming more software-centric and
focused on ready-to-use building blocks and components that
come with a defined, or even standardized, interface and API,
and can easily be integrated. In such a world, motion control
is just one part of a system – often merely a peripheral part
because the major part (from an engineering point of view) is
the application itself..
Increased integration - SoCs, ASICs, and other highly
integrated semiconductors used for motion control can include
analog blocks (ADCs, gate drivers, voltage regulators) and
digital standard blocks (commutation logic, PWM). Recently,
they have also begun to integrate various types of intellectual
property that makes then even smarter and more complex. This
embedded IP can include integrated communication protocol
stacks, signal conditioning tasks, on-the-fly motion profile
calculation, high-end commutation algorithms, and control loops
that makes these devices smarter.
Motion control will become ubiquitous - The world will
become more and more fully automated. Motion control will
continue taking over many more applications, tasks, and needs
within the personal and industrial environments in an unnoticed
way. This will increase requirements on the quality of motion
control in terms of safety, reliability, efficiency, accuracy and
precision. Another emerging requirement is to minimize the
mechanical noise produced by vibrations of the motor and the
devices attached to it.
Fig. 2 Differences in typical stepper motor control architectures