Motion Control System Design

Understanding Motion Control Systems in Modern Industrial Applications

Motion control system design represents one of the most critical disciplines in modern automation engineering. These sophisticated systems govern the precise movement of machinery components, enabling everything from high-speed packaging lines to precision CNC machining centres. For manufacturers across Atlantic Canada, implementing well-designed motion control solutions can dramatically improve productivity, reduce waste, and enhance product quality.

At its core, a motion control system coordinates the movement of mechanical components through a carefully orchestrated combination of controllers, drives, motors, and feedback devices. Whether you're operating a seafood processing facility in Nova Scotia or a precision manufacturing plant in New Brunswick, understanding the fundamentals of motion control design is essential for staying competitive in today's demanding industrial landscape.

The complexity of these systems has increased substantially over the past decade, with modern motion controllers capable of synchronising dozens of axes simultaneously while maintaining positioning accuracy within micrometres. This technological advancement opens tremendous opportunities for Maritime manufacturers looking to automate processes that were previously considered too complex or cost-prohibitive.

Key Components of Motion Control Architecture

A comprehensive motion control system comprises several interconnected components, each playing a vital role in achieving precise, reliable movement. Understanding these elements is crucial for engineers designing new systems or upgrading existing automation infrastructure.

Motion Controllers and Programmable Logic Controllers

The motion controller serves as the brain of any motion control system, executing complex trajectory calculations and coordinating multiple axes of movement. Modern controllers range from standalone units to software-based solutions running on industrial PCs. High-performance controllers can process trajectory updates at rates exceeding 10 kHz, enabling smooth motion profiles even at high speeds.

Many facilities in Nova Scotia integrate motion control functionality directly into their existing PLC infrastructure. Platforms such as Allen-Bradley ControlLogix, Siemens S7-1500, and Beckhoff TwinCAT offer integrated motion control capabilities that simplify system architecture while providing enterprise-level connectivity.

Servo Drives and Variable Frequency Drives

Servo drives convert low-power control signals into high-power currents that drive motors with exceptional precision. Modern servo drives incorporate advanced current control algorithms, operating at PWM frequencies of 8-16 kHz to ensure smooth torque delivery. Key specifications to consider include:

• Continuous current rating: Typically ranging from 2A to 500A depending on motor size

• Peak current capability: Usually 200-300% of continuous rating for acceleration

• Control loop bandwidth: Current loops exceeding 2 kHz, velocity loops of 200-500 Hz

• Communication protocols: EtherCAT, PROFINET, EtherNet/IP, or proprietary networks

• Regenerative capability: Essential for applications with frequent deceleration

Variable frequency drives (VFDs) remain appropriate for applications where precise positioning is less critical, such as conveyor systems or pump control. However, the price differential between VFDs and servo systems has narrowed considerably, making servo solutions increasingly attractive even for simpler applications.

Motor Selection and Sizing

Proper motor selection forms the foundation of any successful motion control project. The three primary motor technologies used in precision motion applications include:

Permanent Magnet Synchronous Motors (PMSM): These brushless motors offer excellent torque density and efficiency, making them ideal for most industrial automation applications. With power ratings from fractional horsepower to several hundred kilowatts, PMSMs suit applications ranging from small pick-and-place systems to large material handling equipment.

Linear Motors: Direct-drive linear motors eliminate mechanical transmission elements, achieving accelerations exceeding 10g and positioning repeatability better than ±1 micrometre. While more expensive than rotary alternatives, linear motors excel in semiconductor manufacturing, precision metrology, and high-speed packaging applications.

Stepper Motors: For cost-sensitive applications requiring moderate precision, stepper motors provide an economical solution. Modern closed-loop stepper systems bridge the gap between traditional open-loop steppers and full servo systems, offering positioning accuracy of ±0.05 degrees at a fraction of the cost.

Motion Profile Design and Trajectory Planning

The motion profile defines how a system transitions from one position to another, balancing speed, smoothness, and mechanical stress. Selecting the appropriate motion profile significantly impacts system performance, energy consumption, and component longevity.

Common Motion Profile Types

Trapezoidal profiles represent the simplest approach, featuring constant acceleration, constant velocity, and constant deceleration phases. While computationally efficient, trapezoidal profiles create instantaneous changes in acceleration (infinite jerk), which can excite mechanical resonances in systems with compliance.

S-curve profiles introduce controlled jerk limits, creating smoother transitions between acceleration phases. Typical jerk values range from 50 to 500 m/s³ depending on mechanical system characteristics. S-curve profiles reduce vibration, minimize settling time, and extend mechanical component life—particularly important for systems operating 24/7 in demanding Maritime industrial environments.

Polynomial and spline-based profiles offer the highest degree of smoothness, with continuous derivatives up to the fifth order or higher. These profiles are essential for applications such as robotic painting, laser cutting, and precision dispensing where path smoothness directly affects product quality.

Multi-Axis Coordination

Many industrial applications require coordinated movement of multiple axes. Consider a typical gantry system used in shipbuilding facilities across Atlantic Canada—such systems require precise synchronisation between X, Y, and Z axes to achieve accurate positioning of welding torches or cutting tools.

Modern motion controllers support several coordination modes:

• Electronic gearing: Slave axes follow master axis movement with configurable ratios

• Electronic camming: Slave axis position is a function of master position, defined by cam tables

• Coordinated path motion: Multiple axes move simultaneously to trace complex paths

• Time-based synchronisation: Axes synchronise to a virtual master time reference

Achieving tight synchronisation requires careful attention to communication network timing. EtherCAT networks, for example, can achieve cycle times below 100 microseconds with jitter less than 1 microsecond, enabling synchronisation accuracy better than 0.001 degrees between axes.

Feedback Systems and Position Sensing

Accurate position feedback is essential for achieving the precision demanded by modern manufacturing processes. The feedback device directly influences system accuracy, resolution, and maximum achievable bandwidth.

Encoder Technologies

Incremental encoders generate pulse trains proportional to movement, with resolutions typically ranging from 1,000 to 1,000,000 counts per revolution. Higher resolution enables tighter velocity loop tuning and smoother motion at low speeds. However, incremental encoders require a homing sequence at startup to establish absolute position.

Absolute encoders maintain position information through power cycles, eliminating homing requirements and reducing startup time—a significant advantage for production equipment. Multi-turn absolute encoders track position across multiple revolutions using battery-backed counters or innovative Wiegand wire technology that harvests energy from rotating magnetic fields.

Resolver-based feedback offers exceptional ruggedness, operating reliably in temperatures from -55°C to +155°C and withstanding severe shock and vibration. This makes resolvers particularly suitable for harsh environments common in Nova Scotia's resource extraction and marine industries.

Advanced Feedback Strategies

For applications demanding the highest accuracy, dual-loop feedback architectures prove invaluable. In this configuration, a motor-mounted encoder closes the velocity loop while a separate load-side encoder closes the position loop. This approach compensates for mechanical transmission errors, backlash, and compliance, achieving positioning accuracy limited only by the load-side sensor resolution.

Vision-based feedback systems are increasingly integrated into motion control architectures, enabling adaptive positioning based on real-time part location. A fish processing system, for example, might use vision feedback to adjust cutting positions based on individual fish dimensions, maximizing yield while maintaining consistent product quality.

System Integration and Communication Networks

Modern motion control systems must integrate seamlessly with broader plant automation infrastructure. Selecting appropriate communication networks ensures reliable data exchange while meeting real-time performance requirements.

Industrial Ethernet Protocols

Industrial Ethernet has largely supplanted traditional fieldbus technologies for motion control applications. The leading protocols each offer distinct advantages:

EtherCAT provides exceptional performance with cycle times as low as 12.5 microseconds and synchronisation accuracy better than 100 nanoseconds. The protocol's distributed clock mechanism ensures precise coordination across large numbers of axes.

PROFINET IRT (Isochronous Real-Time) offers deterministic communication with cycle times down to 31.25 microseconds, integrating seamlessly with Siemens automation platforms prevalent throughout Canadian industry.

EtherNet/IP with CIP Motion provides real-time motion control over standard Ethernet infrastructure, simplifying integration with Rockwell Automation systems commonly found in North American manufacturing facilities.

Safety Integration

Functional safety requirements increasingly influence motion control system design. Safe motion functions, implemented according to IEC 61800-5-2, include:

• Safe Torque Off (STO): Removes torque-generating energy from the motor

• Safe Stop 1 (SS1): Controlled deceleration followed by STO

• Safely Limited Speed (SLS): Prevents motor speed from exceeding defined limits

• Safe Position (SP): Monitors that position remains within specified bounds

• Safely Limited Increment (SLI): Limits total travel distance

Modern servo drives incorporate these safety functions directly, achieving Safety Integrity Level 3 (SIL 3) without requiring external safety relays. This integration reduces wiring complexity while enabling more flexible machine operation modes.

Commissioning, Tuning, and Optimisation

Even the most carefully designed motion control system requires proper commissioning and tuning to achieve optimal performance. This phase often determines the difference between a system that merely functions and one that delivers exceptional results.

Auto-Tuning and Manual Optimisation

Most modern servo drives include auto-tuning functions that characterise motor and load dynamics, then calculate initial control loop gains. While convenient, auto-tuning rarely achieves optimal performance. Experienced engineers typically use auto-tuned values as starting points, then manually refine gains based on observed performance.

Key tuning objectives include:

• Minimising following error during constant velocity motion

• Reducing settling time after rapid positioning moves

• Eliminating overshoot at target positions

• Suppressing mechanical resonances that could cause vibration or instability

• Optimising disturbance rejection to maintain performance under varying loads

Advanced tuning techniques such as notch filtering, feedforward compensation, and adaptive gain scheduling can dramatically improve performance in challenging applications. For systems with significant compliance or backlash, vibration suppression algorithms like Input Shaping reduce settling time by 50-80% compared to conventional control approaches.

Performance Validation

Comprehensive testing validates that the commissioned system meets design requirements. Standard tests include:

Positioning accuracy tests measure the deviation between commanded and actual positions across the full travel range, typically using laser interferometers or calibrated gauge blocks.

Repeatability tests evaluate position consistency over multiple cycles, with statistical analysis providing confidence intervals for expected performance.

Dynamic response tests verify bandwidth, settling time, and following error meet specifications under realistic motion profiles and load conditions.

Partner with Sangster Engineering Ltd. for Your Motion Control Projects

Implementing a successful motion control system requires expertise spanning mechanical design, electrical engineering, and software development. From initial concept through commissioning and ongoing support, the engineering team must understand both theoretical principles and practical realities of industrial automation.

Sangster Engineering Ltd. brings decades of automation experience to manufacturers throughout Nova Scotia, New Brunswick, Prince Edward Island, and the broader Atlantic Canada region. Our engineers have designed and commissioned motion control systems for diverse applications including seafood processing, precision manufacturing, material handling, and custom machinery.

Whether you're upgrading an existing production line or developing new automated equipment, we provide comprehensive engineering services including system architecture design, component selection, control system programming, and on-site commissioning support. Our local presence in Amherst means responsive service and ongoing partnership as your automation needs evolve.

Contact Sangster Engineering Ltd. today to discuss your motion control requirements. Let our team help you achieve the precision, reliability, and productivity that modern manufacturing demands.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.