HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Heat, Ventilation and Damper Control Trendsdecline in price, size, and increases in performance. This will cause themto dominate the market at the expense of stepper motors. Stepper motorswill still have their applications due to stepper drive technologyinnovations.Stepper motors are improving and they have their advantages anddisadvantages. They initially became popular because they ran openloop and were simple to apply. No feedback loop was needed. The controllerjust sends the proper number of pulses and then goes to thisposition. Once in position they do not hunt, as servos can. However,they have some peculiar dynamics, and under certain conditions andspeeds can become unstable. If they miss steps, the system is out ofposition until reset.Microstepping is a way to increase the number of positions that astep motor can assume. It has been refined by the Compumotor Divisionof Parker Hannifin in its OEMZ14 microstepping drive. This drive usesspecial damping circuits for Anti-Resonance and Electronic Viscositydamping. These are designed to defeat the step motor’s resonance effectsand stop any ringing that can occur after quick moves.There are several approaches to the missed-step problem. OrientalMotors’ Alpha Step system uses an integral encoder and automaticallyswitches to closed-loop control if the motor begins to lose synchronization.When the lost steps are made up, the system switches back to openloop.Compumotor uses another approach to the synchronism problem.Its Gemini series can recognize if the motor has stalled without a feedbackdevice, and the method is being extended to allow the step motorto operate closed loop.Linear motors are gaining in performance and popularity, and thistrend is likely to continue. Their ability to eliminate lead screws, gears,pulleys, and the associated complexity and backlash will increase theiruse.Linear motors are increasing in power, precision, and ease of use,while prices are decreasing. This will continue as linear motors prevailas the fastest growing motor segment.NetworkingIntegrating motion control involves more than moving the controland drive into the same package or even moving them into the motor.Integration starts with communication and is focused on open systems.©2001 by The Fairmont Press, Inc. All rights reserved.