Say the word “analog” to most EEs, and thoughts turn to op-amps, power devices, I/O, or signal conditioning circuits. But, the system beyond the circuit is also full of “analog,” if we include everything described by continuous variables and behavior, e.g., the “mechanical” aspects. The word “mechatronics” has been coined for technology that combines electronic and mechanical elements, including the motors and sensors that perform at the interfaces.
In this blog post I’d like to show a few example mechatronic systems that can be modeled and simulated in SystemVision Cloud, a free online schematic capture and simulation platform. The examples demonstrate not only analog circuit designs, but also key elements of the external system including controls, motors/actuators, and dynamic mechanical loads that are essential to understanding the performance of the entire system. The examples also demonstrate the early stage “concept exploration” vs. later stage “implementation verification” phases of the design process.
This first design example shows a stepper motor's ability to control a load angle, not by using a rotation angle sensor for feedback, but rather by simply counting steps. In this case, eight steps are taken in the forward direction, followed by two steps in the reverse direction, repeating this cycle every one second.
The load angle (brown waveform) is seen to increase and decrease as commanded by the direction control signal (light blue waveform) and a 100ms periodic clock input (not shown). But on the fourth step of the second cycle, the windup spring's torque exceeds the capability of the stepper motor, causing it to "snap back" suddenly to a negative angle, below the initial starting point! This “dramatic” result illustrates the need to include all the relevant “system context” when designing a motor and its control electronics.
Note that the switching order of the phase currents of the motor (red and dark blue waveforms) reflect the sequencing of the drive switches in the forward and reverse direction. At this phase of the design process we are trying to explore and verify proper switch sequencing, adequate motor stall torque, step ringing/settling times, and perhaps maximum step rate limits. These design aspects do not require detailed power MOSFET switches and complex gate drive circuits for proper assessment, so ideal digitally controlled switches are being used as they generally allow faster simulation.
This second design example extends the range of interacting technologies, including more detailed analog and digital electronics as well as fluidic aspects. The system includes a DC-motor/pump/pressure-regulator, an electro-fluidic fuel injector, and a mixed-signal drive circuit that regulates the injector current.