Motion control systems literally enable the wheels of industry to turn
Published on : Monday 06-11-2023
Dick Slansky, Senior Analyst, PLM & Engineering Design Tools, ARC Advisory Group.
What is Motion Control technology, and how does it play a critical role in various industries and applications?
Motion Control is a sub-field of automation in general. It encompasses the systems or subsystems involved in the moving individual components of machines in a controlled manner. Motion control systems are used throughout many industries and manufacturing. This would also include precision engineering, biotechnology, and nanotechnology. The actual industries span a broad span of discrete manufacturers from automotive, aerospace & defense, heavy equipment, and machinery, packaging, and printing to hybrid industries like consumer goods, food & beverage, pulp & paper, and high precision micro-manufacturing like semiconductors and medical equipment. Motion control systems literally enable the wheels of industry to turn.
At a basic level, motion control may be open-loop or closed loop. In open loop systems, the controller sends a command through the amplifier to the prime mover or actuator and does not receive information to know if the desired motion was actually achieved. Typical motion control systems would include some type of motor control. To achieve tighter control with more precision, a measuring device would be added to the system, typically near the end motion. This measurement is converted to a signal that is sent back to the controller that can compensate for any errors. This then becomes a closed loop motion control system.
Typically, the position or velocity of the machine is controlled using electric (stepper) motors, hydraulic pumps, linear actuators, or a servo motor. Motion control is an essential component for robotics (kinematics), CNC machines, or less complex general motion control (GMC) used in production lines, conveyance systems, and assembly systems.
What are the key components and principles behind motion control systems, and how do they contribute to precise motion management?
The term ‘motion control’ doesn’t describe a particular component or piece of equipment. Rather it describes a group of individual components that make up a system that functions together to create controlled movement in a machine. The primary components would include:
A motion controller – an electronic device that calculates and controls the mechanical movements or trajectories (motion profile) an actuator must follow, and in closed-loop systems, provides feedback to make control corrections and thus implement closed-loop control. The number of controllers used in any particular motion application, such as in a production line, will vary depending on the number of individual processes that need to be controlled. Typically, each process controller has the ability to receive and provide feedback to a master computer that controls larger work cells or even the entire production line.
A motor drive or amplifier to transform the control signal from the motion controller into energy that is transmitted to the actuator. It interprets the signal from the controller and supplies the correct amount of energy to the motor to achieve the desired motion result.
A primary mover (motor) or actuator. This can take various forms and have many different applications. Their main function is to receive inputs from the motor drive and convert these inputs into motion. Some types of motors and actuators can include:
i. Stepper – Stepper motors can operate in a similar fashion to regular electric motors. However due to the specific arrangement of magnets installed in them, each shaft rotation can be broken down into individual “steps.” This allows for highly accurate positioning of production line components.
ii. Servo – A servo motor provides a very accurate way to control angular motion.
iii. Linear Actuator – These actuators convert the rotational motion of a motor into linear motion similar to a pneumatic cylinder.
These main components, along with subsidiary components such as various sensors and cabling represent the bulk of modern motion control systems.
How has motion control technology evolved over the years, and what are the latest advancements in the field?
Today’s electric motion control systems originated as alternatives to hydraulic motion systems. With most electric systems ranging in size from a few watts into the kilowatt range, electric motion control has become prevalent at these smaller sizes, while hydraulic systems continue to dominate the larger applications around 5kW and higher. The electric systems are more factory-friendly, less obtrusive, and are easier to install than the plumbing required by hydraulics. Early electric servo systems were usually operated in velocity or torque mode, accepted analog command signals, and were quite successful despite problems with electrical noise and drift.
While analog control signals are still used on some systems, most modern motion systems have migrated to some form of digital control. The advent of the digital servo drive, with the ability to close the position loop was another major step forward. New types of signals between the controller and drive are now required to send position commands to these digital servo drives. The three most common control signals used by today’s PLC-based motion controllers are the pulse and direction signals, discrete signals to an intelligent or indexing drive, and fieldbus communications.
A variety of motion controllers are available today. Categories include PLCs, PACs, PC-based, and standalone controllers and microcontrollers. Modern, programmable logic controllers (PLCs) and programmable automation controllers (PACs) have a limited range of motion control capabilities. PC-based systems can expand on many of the PLC and PAC capabilities. Standalone controllers can be part of the drive or separate with a focus on motion control. Individual microcontrollers can be attached to a part of a small drive or can be directly integrated into an all-in-one drive-and-motor combination.
How does motion control technology contribute to energy efficiency and sustainability in industrial operations?
Almost 70 percent of electricity consumed by industry is used by electric motor systems. The next generation of intelligent motion control solutions are delivering significant reductions in energy consumption by moving more motion control applications from fixed speed motors to high efficiency motors and variable speed drives. Motors and motion control have evolved over time: from basic on/off fixed speed motors to complex multi-axis servo drives used in robotics and other precision motion applications.
One significant example of gaining energy efficiency in motion control systems is in closing the loop in actual position versus command position in one of the most used components in motion control: the common stepper motor. Low-cost stepper motors make them popular for automation applications such as indexing and positioning. Because traditional step motor systems run open loop, drive electronics constantly supply current to motor windings, regardless of torque demand from the load. Configured to provide the motor’s rated current, the drive will always try to power the rated current into the motor at all times, whether the motor needs it or not. Expending unnecessary energy during operation makes open-loop step motors inefficient.
Closing the loop simply makes a more efficient step motor system. By employing a common feedback device such as an encoder to monitor actual shaft position versus commanded position, a closed-loop system step motor system automatically reduces current to the motor when torque is no longer demanded by the load requirements. Only the amount of current needed to drive the load powers the motor. This relatively simple conversion multiplied over the hundreds of thousands of stepper motors in use by industry will save a very large amount of energy overall.
What challenges or limitations are associated with motion control technology, and how are they being addressed or mitigated?
There are several challenges facing the motion control market in terms of improving the technology.
Improvement of electric motor drives. These components power a large range of manufacturing and production process lines worldwide. Variable frequency drives (VFDs) that can deliver reliable speed and torque control for the AC induction motor represent one of the largest developments over time. Hardware and software innovations were the enablers for newer generations of electric drives. Dramatic size and weight reduction have been achieved in VFDs. Although smaller than VFDs, servo and stepper drives have also benefitted from ongoing electronic controls miniaturisation. Newer features include growing intelligence built into all types of drives, such as diagnostics and motor/drive tuning.
Software improvements. The equations and motors were available early on, but their implementation into software for more dynamic control programs and algorithms had to wait until computers, and especially microprocessors became commonplace. At the same time, continual performance improvement occurred in MPUs, digital signal processors, and microchips for executing programs in motion control systems. Simulation is a further area of software development. It allows ‘virtual prototyping’ of motion control systems in software simulation before building the hardware. Simulation allows system designers to check out complex motion system details and explore potential design options and alternatives.
Mechatronic integration. Mechanical and electronic systems traditionally worked as physically separate systems. The motion control space experienced a significant change starting in the late 1990s when electric motor and control integration was introduced. There are various benefits to having control electronics onboard motors that include lower installation costs, fewer system components, easier diagnostics and maintenance, and simpler controls architecture. As mechatronic integration matured, its implementation in manufacturing plants expanded to serve multiple motion axes. This has promoted decentralised or distributed control architectures, which connect to the overall factory control system via fast communication networks.
As mentioned in the response to question one, motion control is a sub-field of general automation, and today motion control technology is totally integrated into complex automation systems such as robotic work cells, automated assembly systems, and throughout just about any manufacturing production line.
Today’s advanced robotic systems are being enabled with AI and machine learning (ML) that are enabling a next generation of intelligent robots (cobots) that can work alongside their human counterparts. Not only will AI algorithms drive the advanced kinematic motion required for these robots, but it will enable a set of cyber capabilities that will make these robot helpers more human-like. By 2025, it is expected that human-centric Cognitive AI systems with higher machine intelligence will emerge. These intelligent machines will be able to understand language, integrate commonsense knowledge and reasoning, and adapt to new circumstances. These capabilities will unlock a new set of competencies, ushering in next-generation AI applications for kinematic control. Cognitive AI integrates technologies such as speech recognition, advanced computer vision systems, machine learning, natural language processing (NLP), video analytics, and advanced kinematics into a single architecture that will offer new levels of functionality.
In the area of motion control systems ML algorithms can figure out exactly what the motion profile should look like. Because the motors driving the system need to be coordinated in real-time, the motion profile is built into the machine control because it can’t be done on a factory server or an edge device.
Today, closed-loop control with AI allows motion designers to feed data into predictive models that can optimise output based on past performance parameters, thus optimising the work cell and overall production process. PLC suppliers now offer AI modules for closed-loop control.
Dick Slansky is Senior Analyst, PLM & Engineering Design Tools, ARC Advisory Group.
Dick's responsibilities at ARC include directing the research and consulting in the areas of PLM (CAD/CAM/CAE), engineering design tools for both discrete and process industries, Industrial IoT, Advanced Analytics for Production Systems, Digital Twin, Virtual Simulation for Product and Production. Dick brings over 30 years of direct experience in the areas of manufacturing engineering, engineering design tools (CAD/CAM/CAE), N/C programming, controls systems integration, automated assembly systems, embedded systems, software development, and technical project management. Dick provides technical consulting services for discrete manufacturing end users in the aerospace, automotive and other industrial verticals. Additionally, he focuses on engineering design tools for process, energy, and infrastructure.
(The views expressed in interviews are personal, not necessarily of the organisations represented)