AC Flux Vector Drive Reduces Chain Wear for Poultry Processor

The following case history details how an AC flux vector drive was used for processing-line speed control and motor load-sharing demands for a Midwestern poultry processor. The study is based on an interview with Dick Nowlin, Senior Systems Integrator for Motion Industries, Inc., Little Rock, AR.

The Problem
Processing lines that require precise speed regulation often have multiple, mechanically connected drives that compete to regulate the speed. Since the set points are not perfect, the result is drives fighting each other. A typical application might involve a long line shaft, a traction vehicle, or a chain, as in the case of this Midwestern poultry processor.

The Situation
The problem that the poultry processing plant faced was that of maintaining an even flow on their processing lines. The continuous, chain-driven line, which moves up and down, turns and jogs, needed to move smoothly. But when the uphill load was heavier than the downhill load or the chain jerked for any reason, product moving along the line began swaying, or even fell off the line, which added even more variance and strain to the mechanical system. The result is chain and sprocket wear and premature motor failures caused by inconsistent speed.

At the poultry plant, three processing lines were addressed. Two of the lines used three four-pole, 1800 RPM, 3-hp motors. The third line ran faster and used three 3-hp 3600 RPM motors.

At the company's older plants, engineers had tried multi-motors and a single inverter, as well as hydraulic drives. But nothing controlled the speed consistently and provided adequate load-sharing between the motors. Speed inconsistency creates a problem of time. Too little time in any process introduces the possibility that any of the successive processes are not fully completed. Too much time means the line is not as productive as it should be.

Whenever the necessary line speeds (established by the FDA) are not maintained, inspectors in food processing plants might call for a line shutdown, and all product on the line must be discarded. Shutdown, start-up, and the time-consuming FDA paperwork increase downtime. In other words, incorrect line speeds can be extremely costly for food processors.

To address the problem, the processor eventually enlisted the services of Motion Industries, Inc., a nationwide industrial distributor systems integrator in Little Rock, whose engineers had solved this same problem for other poultry plants.

Lessons Learned From Experience
In the early 90's, Motion Industries had addressed all kinds of material handling processes and, thanks to some particularly tough jobs, already knew what not to do.

One such tough job was for a company that manufactured automobile wheels, and had almost a mile of overhead conveyors. Approximately every two feet, a wheel hung from a shackle. The load varied considerably between no load and full load, with infinite steps in between. Throughout the process, the conveyors moved up, down, and around, "and had tremendous dynamics - lots more than a poultry processor's lines. It was the same process, just on a larger scale."

Dick Nowlin, Senior Systems Integrator for Motion Industries, Inc., remembers having tried numerous solutions: AC drives with multi-motors and AC drives with more than one drive. Each time they learned a bit more. Eventually, the solution seemed imminent using DC motors and additional front-end controls for the DC drives, but it wasn't stable enough. The reason was the inconsistent tensioning system. When there was any slack in the line, it tended to creep into any area having the least amount of pull.

"We learned that in order to maintain consistent speed and consistent torque or load sharing, you have to have consistent tension."

The Solution: AC Flux Vector Drives
In 1992-93, a company named Thor Technology was beginning to develop and apply flux vector technology. And when Motion Industries began studying the troublesome line at the poultry plant, Nowlin felt the application fit the profile of the tough motion and timing challenges being solved by Thor's new flux vector drive. He felt that load-sharing AC induction motors with Thor's Series 7000 AC flux vector servo control was the best answer for these processing line problems.

In discussing the flux vector drive solution with Nowdin, Thor said that it could be made to work with inverters, but not with the same trimming capability.

"We really didn't know anyone at that time who could effect the fine tuning of the followers without, perhaps, a specially designed product. But once we realized that the flux vector drive had the capability of using a load signal as a trim function to the follower drives, we felt certain that it would work."

Thor agreed that this was an ideal flux vector servo application, and the drive manufacturer developed software parameters for load-sharing that could address this situation in any continuously moving, closed loop line.

Parameter-Driven Software
Thor's flux vector drives are controlled by parameter driven software that can be set in the field. Precise speed monitors are installed for use by the FDA inspectors. The solution worked so well that FDA "speeding tickets" have been eliminated on lines having Thor controls.

The type of motor drive software used can determine the simplicity of field installation and adaptation to particular processes. Motor control drives may use software to adapt to the application. As in any computer, two types of software are present:

• a permanent operating software, burned in the PROM
• the field variable, application building blocks

The application building blocks are adjustable at the application engineering level. A software parameter table gives the motor owner a wide range of capabilities for adapting controls to a specific application. While factory-set, fine-tuning is expected by adjusting or reloading the parameters in the field.

To reconfigure Thor's flux vector building blocks, the engineer has almost 671 available parameters. Typically only 7-10 will be reset in the field. These correspond to the DIP switches, potentiometers, and plug-ins found in older drives.

System Design
According to Thor's Joe Pottebaum, chief applications engineer, "The system design supports load-sharing, but because of the difference between no-load to full-load, we can run the line in the actual speed mode, rather than the torque mode."

The solution uses the master and slave method where the master drive sets the line speed. The two main drives are hooked together in the slave mode.

The system at the poultry processing plant consists of:

• 3 three Hp motors
• 3 Controls
• 3 Inverters

Cost/Benefit Analysis
Flux vector drives have a higher initial cost. However, experience has shown that the Thor drives have little downtime. AC motors, on the other hand, have both a lower initial cost and lower maintenance costs than DC motors, which justifies the additional up-front investment. And when the cost of downtime is also factored into the equation, the AC flux vector drives prove cost effective.

Thor Technology Corp. (Milwaukee, WI) designs and manufactures AC Flux Vector motor controls and supplies engineered drive systems and custom drive solutions for a wide range of commercial, industrial automation, medical, and military applications.

Motion Industries, Inc. is a distributor and manufacturer's rep for many major manufacturers of electrical and electronic equipment. The company has 393 branches throughout the US. Its parent company is Genuine Parts Company, Birmingham, AL.

For information contact Thor Technology Corp., PO Box 25903, Milwaukee, WI 53225. Tel: 414-252-2200; Fax: 414-252-2201. Motion Industries, Inc., 5312 W. 65th St., Little Rock, AR 72209. Tel: 501-565-4413; Fax: 501-565- 1626.