What are General Motion Control (GMC) Systems?

By Sal Spada

Category:
Industry Trends

General Motion Control (GMC) Systems business has a highly fragmented supplier base. This fragmentation is a result of several factors, including niche market opportunities and diversity in control architectures. Accordingly, GMC systems business includes both individual GMC component sales and revenues generated by bundling one or more GMC components.

Control system architectures vary widely depending on several factors in the target market. For example, many original equipment manufacturers (OEMs) and system integrators (SIs) in the semiconductor industry have the in-house expertise to purchase components from many different suppliers to develop an integrated control system. Alternatively, low volume specialty machine producers and end users prefer turnkey solutions requiring minimal systems integration expertise. These classes of users each present GMC suppliers with a divergent set of requirements.

GMC systems provide the ability to precisely control position, velocity, and torque of a rotational or linear electro mechanical device. Precise control of the end-effectors directly translates into the motion imparted on the linear or rotary mechanism. A common set of mechanical configurations found in industrial automation includes rotary tables, positioning tables, and cylindrical rollers.

This study focuses specifically on electronic motion control systems used in the industrial automation market and excludes industries and applications that fall outside of this definition. Specifically, the results do not reflect supplier revenues derived from military, aerospace, consumer products, and office automation equipment markets. Revenues from on-board mo-tion control equipment for vehicles are also excluded. In addition, revenues from motion control equipment used in the CNC market are ex-cluded from this GMC report. ARC generates a separate report for the CNC market.

General Motion Control (GMC) System Components

Each GMC system includes three generally accepted functional elements: controller, drive, and motor. Several possible configurations add to the va-riety of offerings available. The motion controller can be offered as an integral portion of the drive system, a standalone system, or a bus-based module with external drive interface signals.

Excluded products include: hydraulic and pneumatic actuators, linear and rotary mechanical positioning stages, and couplings, gearboxes, and posi-tional feedback devices sold as separate components.

Motion Controllers

The motion controller is capable of coordinating and synchronizing the ro-tational or linear position of one or more axes of motion. In general, the motion controller has an on-board application program, developed by the end user or system integrator when adapting to the requirements of a ma-chine. The motion controller provides the path planning, velocity, and acceleration profiling for one or more axes of coordinated mo-tion. Four types of motion controllers are generally available:General Motion Control System Components

Standalone Motion Controller

Standalone motion controllers continue to dominate shipments in the market today, despite the presence of PLC and PC-based motion controllers. This popularity stems from economical pricing and packaging, and the fact that many have integrated logic processors with sufficient discrete and analog I/O for many applications.

Generally, a standalone controller has a dust-proof enclosure, built-in pow-er supply, communication link for commissioning and programming with Windows-based software, networking ports, and heavy gauge terminal

blocks for field wiring. To meet constraints imposed by lack of space, some vendors offer the motion control modules integrated with the drive. In cas-es where the motion controller is integrated on the drive, it typically uses the same processor for executing the motion control program and for closed loop compensation.

PLC-Based Motion Controller

The motion controller module of a PLC-based system typically includes a dedicated processor that executes a user-installed motion control program. This study includes revenues from PLC motion modules, drives, and mo-tors. The study revenue total does not include ancillary components sold with the system, such as CPUs, power supplies, racks, and I/O.

PLC-based motion controller modules support single and multi-axis appli-cations. Common drive interfaces include analog velocity or torque command for servo systems, and pulse and direction output for stepper systems. Motion control networks are used in larger axis count systems. Typically, the motion module shares the PLC power supply and communi-cates with the main processor through the standard PLC backplane or device networks. The motion controller module can exchange information from devices connected to the same, or another, PLC via the PLC back-plane, remote I/O drops, or standard device networks.

The motion controller module can be programmed using a PC or standard PLC terminal. Either of these devices can also function as an operator inter-face. Most PLC suppliers now have common motion control and logic programming environment. Specifically, some high-end PLC platforms have evolved into programmable automation controllers (PAC), in which logic and motion control functions are integrated and provide the integrat-ed development environment (IDE) for multi-control domains.

PC or Bus-Based Motion Controller Cards

Bus-based GMC systems include intelligent motion control boards for PC bus, as well as those that are compatible with standard buses, such as VME, PCI, Compact PCI, PC104, and STD32. Bus-based GMC systems include intelligent motion control boards that are compatible with standard buses, such as VME. They are most commonly integrated with general-purpose host controllers. Motion controllers are mounted within racks along with a main processor, industrial I/O, and memory modules. Programming of the motion controller board is accomplished by using a PC with software de-velopment tools provided by the board vendor.

For PC-bus GMC systems, the motion controller module is plugged into the PC chassis and the PC treats the motion controller module as it would any coprocessor. The same PC can be used for programming and operating the system. This segment includes the ISA, PC104, and PCI bus products. Hardware revenues derived from PC hosts are not included in this study. Only those hardware revenues resulting from the sale of motion control cards, drives, and motors are included.

PC–Based Motion Controller Software with Interface Hardware

A PC-based soft motion controller is marketed as a software application in conjunction with an unintelligent adapter interface to a drive. The motion control software is loaded directly onto a standard PC and the adapter interface is plugged into the PC backplane. The drive adapter interface utilizes either a standard analog command or digital drive interface.

The supplier of the motion control card generally has a number of software drivers available that support a range of real time operating systems for the Industrial PC platform. Typical programming languages supported in-clude Visual BASIC, Visual C++, or C++.

Drive Amplifier

The drive amplifier provides electrical power to the motor, regulating the motor speed and torque in response to commands from the motion control-ler. The drive in a GMC system functions as the interface between the motor and the motion controller. The drive is responsible for delivering current to each of the motor windings. The type and size of motor used determines the drive that needs to be selected for an application. In GMC applications, drives can be broadly classified into stepper and servo drives. Typically, a stepper drive does not need a feedback device. Therefore, it acts in an open loop fashion. In contrast, servo drive systems require feed-back for stable system operation.

The command interface to the motion controller is distinctly different be-tween stepper drives and servo drives. Typically, stepper drives have adopted a pulse train with direction input command interface, whereas servo drives adopted the +/-10 Volt velocity or torque command interface. In servo drives, a minimum drive configuration consists of a torque loop, although the most prevalent configuration on the market today is the veloc-ity control drive, which has a torque loop commonly referred to as a current loop.

Some drives may have network interfaces, with motion control or pro-grammable moves capabilities. In the past, these were called intelligent drives.

Motor

The motor is the prime mover or actuator accepting appropriate power from the drive amplifier to effect rotary motion of the motor output shaft or linear translation of the slide in a linear motor. The classes of motors in-cluded in this study are stepper, permanent magnet brush-less servo, and permanent magnet brush servo.

Feedback Sensors

Feedback sensor devices are coupled to the motor shaft, or along the axis of movement, to provide position and velocity status data to the drive amplifier and/or the motion controller. Feedback sensors generally include one or more of the following types of devices: encoder, resolver, or linear scale.

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