High performance positioning system

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A high performance positioning system (HPPS) is a type of positioning system consisting of a piece of electromechanics equipment (e.g. an assembly of linear stages and rotary stages) that is capable of moving an object in a three-dimensional space within a work envelope. Positioning could be done point to point or along a desired path of motion. Position is typically defined in six degrees of freedom, including linear, in an x,y,z cartesian coordinate system, and angular orientation of yaw, pitch, roll. HPPS are used in many manufacturing processes to move an object (tool or part) smoothly and accurately in six degrees of freedom, along a desired path, at a desired orientation, with high acceleration, high deceleration, high velocity and low settling time. It is designed to quickly stop its motion and accurately place the moving object at its desired final position and orientation with minimal jittering.

Contents

HPPS requires a structural characteristics of low moving mass and high stiffness. The resulting system characteristic is a high value for the lowest natural frequency of the system. High natural frequency allows the motion controller to drive the system at high servo bandwidth, which means that the HPPS can reject all motion disturbing frequencies, which act at a lower frequency than the bandwidth. For higher frequency disturbances such as floor vibration, acoustic noise, motor cogging, bearing jitter and cable carrier rattling, HPPS may employ structural composite materials for damping and isolation mounts for vibration attenuation. Unlike articulating robots, which have revolute joints that connect their links, HPPS links typically consists of sliding joints, which are relatively stiffer than revolute joints. That is the reason why high performance positioning systems are often referred to as cartesian robots.

Example of custom XYZ configuration with linear motor stages for XY and a ball screw for Z XYZ positioning system.png
Example of custom XYZ configuration with linear motor stages for XY and a ball screw for Z

Performance

HPPS, driven by linear motors, can move at a combined high velocity on order of 3-5 m/s, high accelerations of 5-7 g, at micron or sub micron positioning accuracy with settling times on order of milliseconds and servo bandwidth of 30-50 Hz. Ball screw actuators, on the other hand, have typical bandwidth of 10-20 Hz and belt driven actuators at about 5-10 Hz. The bandwidth value of HPPS is about 1/3 of the lowest natural frequency in the range of 90-150 Hz. Settling time to +/- 1% Constant Velocity, or + / - 1 um jitter, after high acceleration or high deceleration respectively, takes an estimated 3 bandwidth periods. For example, a 50 Hz servo bandwidth, having a 1 / 50 · 1000 = 20 msec period, will settle to 1 um position accuracy within an estimated 3 · 20 = 60 msec. The lowest natural frequency equals the square root of system stiffness divided by moving inertia. A typical linear recirculating bearing rail, of a high performance positioning stage, has a stiffness on order of 100-300 N/um. Such a performance is required in semiconductor process equipment, electronics assembly lines, numerically controlled machine tools, coordinate-measuring machines, 3D Printing, pick-and-place machines, drug discovery assaying and many more. At their highest performance HPPS may use granite base for thermal stability and flat surfaces, air bearings for jitter free motion, brushless linear motors for non contact, frictionless actuation, high force and low inertia, and laser interferometer for sub micron position feedback. On the other hand, a typical 6 degrees of freedom articulated robot, with 1 m' reach, has a structural stiffness on the order of 1 N/um. That is why articulated robots are best being employed as automation equipment in processes which require position repeatability on the order of 100's microns, such as robot welding, paint robots, palletizers and many more.

History

The original HPPS were developed at Anorad Corporation (now Rockwell Automation) in the 1980s, after the invention of brushless linear motors by Anorad's Founder and CEO, Anwar Chitayat. Initially HPPS were used for high precision manufacturing processes in semiconductor applications such as Applied Materials, PCB Inspection Orbotech and High Velocity Machine Tool Ford. [1] In parallel linear motor technology and their integration in HPPS, was expanded around the world. As a result, in 1996 Siemens integrated its CNC with Anorad linear motors to drive a 20 m' long Maskant machine at Boeing for chemical milling of aircraft wings. [2] In 1997 FANUC licensed Anorad's linear motor technology and integrated it as a complete solution with their CNC products line. [3] And in 1998, Rockwell Automation acquired Anorad to compete with Siemens and Fanuc in providing a complete linear motor solutions to drive high velocity machine tools in Automotive transfer lines. [4] Today linear motors are being used in hundreds of thousands high performance positioning systems, which drive manufacturing processes around the world. Their market is expected to grow, according to some studies, at 4.4% a year and reach $1.5B in 2025. [5]

High Performance Positioning System - Gantry Type HPPS.png
High Performance Positioning System - Gantry Type

System requirements

Applications

Specifications

System specification (technical standard) is an official interface between the application requirements (problem), as described by the user (customer) and the design (solution) as optimized by the developer (supplier).

Environment

Example of high performance positioning system with a system analysis simulation model Laser Scribing.png
Example of high performance positioning system with a system analysis simulation model

System solution

Configuration

HPPS configuration is typically optimized for maximum structural stiffness with maximum damping and minimum inertia, smallest Abbe error at the point of interest (POI), with minimum components and maximum maintainability.

System analysis

System analysis is a process of understanding the relationships between design parameters, operating conditions, environmental variables and system performance based on system modeling and analysis tools

Component sizing

Component sizing is the process of selecting standard parts from component suppliers, or designing a custom part for manufacturing

System testing

System testing is an iterative process of system development, intended to validate system analysis modeling, proof of concepts, safety factor of performance specifications and acceptant testing.

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<span class="mw-page-title-main">Industrial robot</span> Robot used in manufacturing

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<span class="mw-page-title-main">Stewart platform</span> Type of parallel manipulator

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<span class="mw-page-title-main">Cartesian coordinate robot</span> Robot with axes of control that are linear and orthogonal

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<span class="mw-page-title-main">Ultrasonic motor</span>

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<span class="mw-page-title-main">Anwar Chitayat</span> American inventor and business executive

Anwar Chitayat is the founder and former CEO and chairman of Anorad Corp., which was acquired in 1998 by Rockwell Automation. Mr. Chitayat holds over 95 patents in Electronics, Semiconductors and Automation including Nanotechnology, Interferometry and Linear motors. His achievements in High technology were honored by SEMI in 2000 at their highest honor for Lifetime Achievement, reserved for individuals who repeatedly enable and lead the technology industry throughout their professional career. In 1997, Anwar was awarded the Entrepreneur of the year award by Ernst and Young, and in 2009, Anwar was inducted to Long Island Hall of Fame for his impacts on science and technology on Long Island.

<span class="mw-page-title-main">Force control</span> Force control is given by the machine

Force control is the control of the force with which a machine or the manipulator of a robot acts on an object or its environment. By controlling the contact force, damage to the machine as well as to the objects to be processed and injuries when handling people can be prevented. In manufacturing tasks, it can compensate for errors and reduce wear by maintaining a uniform contact force. Force control achieves more consistent results than position control, which is also used in machine control. Force control can be used as an alternative to the usual motion control, but is usually used in a complementary way, in the form of hybrid control concepts. The acting force for control is usually measured via force transducers or estimated via the motor current.

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Further reading