The design of motor control systems doesn’t have to be complicated. With Trinamic’s industry-leading technologies embedded in plug-and-play building blocks, Engineers can boost their product development with advanced features. Ranging from extremely smooth and silent control to field-oriented control integrated in hardware, Trinamic makes it as easy as 1-2-3.
Stepper motors typically use a permanent magnet as a rotor, and motor coils as a stator. By sending an electrical current through the motor coils, an electromagnetic field is created which forces the magnetic rotor into the desired position. A hybrid stepper motor allows up to 200 full steps, meaning 200 positions per full 360º revolution. However, smaller steps like half steps or microsteps can be generated using additional current states. This increases accuracy, torque, and efficiency of the motor while reducing step loss, vibrations, and noise.
For each STEP signal sent to the stepper motor driver, MicroPlyer can produce up to 256 microsteps for increased performance. The flexible interpolater unit by Trinamic does so by interpolating the time in between two step pulses, determining the step rate by measuring the time interval of the previous step period and dividing it up into equal parts. Allowing for microstepping with lower resolution step inputs starting from full step, MicroPlyer allows you to easily optimize stepper motor drives of existing designs without the need for changing the entire setup.
Field-oriented control is the most efficient way to drive motors. It transforms actual phase currents from stator-fixed to field-synchronous coordinate systems by using two simple mathematical transformations. The resulting coordinate system has only two dimensions (magnetic flux and torque) which are orthogonal components. Since these can be visualized as a vector, FOC is also known as vector control. Originally developed for high-end applications and difficult to implement, Trinamic offers field-oriented control as an easy to use hardware building block.
Without feedback, the system always assumes that motors behave as expected. And while under common conditions the position of a motor is deterministic and predictable, many devices demand feedback from the motor for added safety and monitoring purposes. Closed-loop operation of motors can furthermore increase efficiency and overall performance of your application, for example by reducing the current when the motor is in standby and increasing the current under load conditions. As such, closed-loop control increases the system's control reliability and flexibility.
One way of providing feedback to the system is SensOstep. This cost-effective solution for detects step losses using a magnetic encoder mounted at the rear of the motor axis and a HALL sensor IC with integrated signal processing mounted on a PCB. Since the sensor resolution needed for detecting a pure step loss is comparatively low and all components are already mounted, SensOstep reduces error margins during assembly to a minimum while speeding up design cycles. Using a serial interface, it reports directly to the processor for ease of integration.
Stepper motors use a fairly simple circuit including switches for directing the current flow through the motor coils. To drive the motor, a current can flow in either direction through the coil from the power supply to ground (ON) or from ground to power supply to brake the motor (fast decay). However, it's also possible to circulate the coil current in a stepper motor via the high-side or via the low-side MOSFETs. This is called passive braking since it slows down the rotational speed without costing any supply current.
Stepper motors typically use a permanent magnet as a rotor, and motor coils as a stator. By sending an electrical current through the motor coils, an electromagnetic field is created which forces the magnetic rotor into the desired position. This electrical current, however, has to be chopped in such a way that the motor behaves as desired. A constant off-time PWM chopper is the classic way to drive a stepper motor but introduces noise and vibration to the mechanical system. Over the years, Trinamic has perfected chopper modes resulting in silent, perfect motor control.
Trinamic's advanced chopper mode offers smooth operation and good resonance dampening over a wide range of velocities and loads. The current chopper introduces a hysteresis function to the classical TOFF chopper, introducing an extra slow decay phase resulting in as little fast decay as possible. This not only increases energy efficiency, the smoother transition also removes the zero-crossing plateau for near-perfect sinewaves. With SpreadCycle, you have an exact representation of the specified current, leading to better operation of the motor at all velocities.
While the advanced current-controlled PWM chopper improves motor behavior, there is still some noise and vibration which can be critical for certain applications. That's because a current-regulated chopper always reacts to the coil current measurement on a cycle-by-cycle basis resulting in noise and electric and magnetic coupling between the motor coils, which in turn influence the current chopper. The voltage-regulated chopper StealthChop overcomes this by modulating the current based on the PWM duty cycle, resulting in a perfect current sinewave.
The sensorless load measurement technology StallGuard provides cost-effective real-time feedback on load angles. By measuring the back EMF of a motor, it knows when a motor is likely to stall and send a signal to the system. While used primarily to safely detect motor stalls, for homing procedures, and to replace mechanical end switches, it can also be used to monitor other aspects of your application. For example, if you know the load conditions under normal circumstances, StallGuard can be used to flag mechanical issues for inspection or predictive maintenance.
The sensorless load-dependent current control CoolStep is based on the StallGuard load values. It detects the motor load by changes in the back EMF and adapts the current to the actual load conditions. As a result, CoolStep always drives motors at their optimum current, saving tremendous amounts of energy by reducing the current to a minimum when the motor has a light load, and increasing the current when the load increases. This not only keeps the motor cool, it also allows short current boosts. CoolSteps improves reliability of the entire system.
By providing extra torque to match sudden increases in mechanical load, DcStep makes sure step count is preserved in overload-situations. So, while most open-loop stepper drives will lose steps in an overload situation, DcStep will reduce velocity to overcome any resistance. This combines the benefits of a DC motor with those of a stepper motor and significantly reduces safety margins of a stepper motor control system. Furthermore, DcStep addresses the stepper motor drive's needs to maintain position awareness and step count without feedback circuitry.