ni motion control fundamentals

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Motion Contro l FundamentalsOverviewAlmost any automated equipment, ranging from industrial machines to medical devices, requirescomponents that perform movement in a controlled way. The most common solution to move a load is usingelectromechanical components such as motors. Learn how to control motor-based systems and explore thedifferent motion control solutions National Instruments provides.

Motion Control RequirementsThe most common motors in the industrial and embedded space are stepper, brushed, and brushless DCmotors, but there are other motor options. Each motor requires individual input signals to spin the motor andtransform electrical energy into mechanical energy. In the broadest sense, motion control helps you use themotor that best meets your application requirements without dealing with all the low-level signaling needed tospin a motor.In addition, motion control provides high-level functions so you can efficiently implement custom applicationsbased on building blocks to create solutions for common tasks like precise positioning, synchronization ofmultiple axes, and movement with defined velocity, acceleration, and deceleration.Because most of the motors are operated during transient circumstances, motion control tools need to adaptto different loads and dynamic conditions, which requires complex control algorithm processing and feedbackinformation from the mechanical system. Last but not least, motion tasks are usually mission-critical andoften operate machines that could harm humans around them. Therefore, security features such as limitswitches and I/O channels are required to collect status information and execute shutdown routines.

Motion Control System ComponentsThe following diagram illustrates the essential components of a motion control system.

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The motion controller uses the trajectories it calculates to determine the proper torque command to send tothe motor amplifier and actually cause motion. The controller also must close the control loop and managesupervisory control by monitoring the limits and emergency stops to ensure safe operation. Each of theseoperations needs to occur in real time to ensure the high reliability, determinism, stability, and safetynecessary to create a working motion control system.

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Control loop - Performs fast, closed-loop control with simultaneous position, velocity, and trajectorymaintenance on one or more axes. The control loop handles closing the position/velocity loop based onfeedback, and it defines the response and stability of the system. In stepper systems, a step generationcomponent acts as the control loop. The loop contains an interpolation component, or spline engine, thatinterpolates between setpoints calculated by the trajectory generator. This enables the control loop toexecute faster than the trajectory generator. Figure 2 il lustrates the functional architecture of NI motioncontrollers.Motion I/O - Serves as the analog and digital I/O that sends and receives signals from the rest of the motioncontrol system. Typically, the analog output is used as a command signal for the drive, and the digital I/O isused for quadrature encoder signals as feedback from the motor. The motion I/O performs positionbreakpoint and high-speed capture. Also, the supervisory control uses the motion I/O to achieve a specificrequired functionality, such as reacting to limit switches and creating the movement modes needed toinitialize the system.National Instruments offers two approaches to implement high-performance motion control systems:

DSP-based plug-in motion controllers for PCI or PXICustom motion controllers using the National Instruments LabVIEW NI SoftMotion Module

Figure 3. DSP-Based Plug-In Motion Controllers

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Figure 4. Custom Motion Controllers Using the LabVIEW NI SoftMotion ModuleDSP-Based Plug-In Motion ControllerNational Instruments provides a variety of plug-in motion controllers that range from high-performancecontrollers with ful l-feature capability for sophisticated requirements to lower-cost motion controllers forpoint-to-point motion applications with solid performance. To enable fast servo update rates of up to 30 kHzfor high-precision applications, these controllers use a dual-processor architecture. These two processors, acentral processing unit (CPU) and a digital signal processor (DSP), form the backbone of the NI motioncontroller.The controller CPU is a 32-bit microcontroller running a multitasking, embedded real-time OS. It offers theperformance and determinism needed to meet most complex motion application needs. The CPU performscommand execution, host synchronization, I/O reaction, and system supervision.The DSP has the primary responsibility of fast, closed-loop control with simultaneous position, velocity, andtrajectory maintenance on multiple axes. It also closes the position and velocity loops, and directlycommands the torque to the drive or amplifier. Motion I/O occurs in hardware on

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noncustomizable field-programmable gate arrays (FPGAs) and consists of limit/horne switch detection,position breakpoint, and high-speed capture. This ensures very low latencies in the range of hundreds ofnanoseconds for breakpoints and high-speed captures.The motion controller processor is monitored by a watchdog timer, which is hardware you can use toautomatically detect software anomalies and reset the processor if any occur. The watchdog timer checks forproper processor operation. If the firmware on the motion controller is unable to process functions within 62ms, the watchdog timer resets the motion controller and disallows further communications until you explicitlyreset the motion controller. This ensures the real-time operation of the motion control system.These PCI- or PXI-based plug-in motion devices are designed for reliable and precise control within aWindows or real-time OS. They provide reduced development time through powerful APls and support withininteractive tools such as the NI Motion Assistant. The highest-performance National Instruments motioncontroller family is the NI 7350 Series, which offers up to eight axes of stepper or servo motion control, extraI/O, and many powerful features including sinusoidal commutation for brushless motors and 4 MHz periodicbreakpoints or position triggers for high-speed integration. Because these plug-in motion controller devicesare based on PCI or PXI, you can integrate them with a wide variety of additional I/O modules and easilycombine them with additional hardware for data acquisition or image processing. To connect the motioncontrol devices to drives and motors, NI provides several cabling and connector block options.Custom Motion ControllersWhile plug-in motion controllers with DSPs are suitable for many applications, you need customized motioncontrollers for high-precision motion control with servo update rates as fast as 200 kHz. Some of theapplications that require such a high level of precision and flexibility include wafer processing machines inthe semiconductor industry or the inline vehicle sequencing (ILVS) reconfigurable-at-run-time assembly linefor the automotive industry.National Instruments reconfigurable I/O (RIO) technology combined with NI SoftMotion technology providesthe right tools for machine builders who want high-precision customized motion control with the flexibility ofan FPGA. In addition to high-precision applications, machine builders and OEMs can use the LabVIEW NISoftMotion Module to implement multiaxis coordinated motion control using the LabVIEW graphicaldevelopment environment on a variety of platforms. For applications that require rugged and compactsystems, you can use NI CompactRIO programmable automation controllers (PACs). By combining thehigh-level function block API of LabVIEW NI SoftMotion and new NI C Series drive interfaces, you canquickly develop powerful motion applications and connect to hundreds of stepper and servo drives.

Additional ResourcesGetting Started with LabVIEW NI SoftMotionWhat is Motion?Advanced Motion using CompactRIO

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