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By John Lewis, Northeast Technical Editor -- Design News, February 17, 1997
Smart conveyor system employs distributed control
Bristol, CT--Competition forces manufacturers such as Warner Electric Linear and Electronics to constantly improve productivity and cut costs on the factory floor. Until recently, workers transported Warner's electric-motor parts from machining to washing and assembly cells by hand-stacking pallets and moving them with hand trucks.
Baskets weighing as much as 100 lbs were stacked on a pallet and wheeled to a manually loaded parts washer. To reduce manufacturing lead time, improve throughput and improve cell layout, Warner purchased an automatic parts washer from Terryville, CT-based Frank J. Coscina Associates, Inc. "What we needed was a conveyor system that would convey parts directly from the machining cells to the washer," says Warner engineer Paul DellaVecchia.
Engineers considered installing a line-shaft conveyor system to improve production flow. The problem: once installed, line-shaft conveyors are not easily moved. "We're always looking for ways to improve our process," says DellaVecchia, "most conveyor systems would only get in the way during future cell changes."
Line shaft conveyors require belts, pneumatic lines, mechanical actuators, and controllers. Five motors running 16 hours/day, 240 days/year would power the proposed line shaft conveyor. Noisy and difficult to move, this type of system also costs lots to maintain. Brian Walker of A-Lineo Material Handling (East Hartford, CT) proposed using Wilmington, NC-based Interroll Corp.'s INTELLIVEYORTM conveyor system to resolve these problems. Distributed controllers, sensors, and motors reportedly make the conveyor flexible, quiet, efficient, and simple to maintain.
Intelliveyor integrates several Interroll products into one system. Several 24-inch zones form the conveyor. Fastened to the floor with two bolts, each zone is easily installed or removed. Networked by ordinary phone lines, compact distributed-control modules mount into the conveyor frame. Onboard DIP switches allow customized control menu selections, eliminating the need for reprogramming in ladder logic or other control languages used by traditional conveyor systems.
Each zone includes at least one DRIVEROLLTM roller with its own self-contained power transmission system. The roller design eliminates the need for chains, line shafts, or other drive elements. It operates at 24 Vdc, and all rollers employ spring-loaded tapered shaft axles that are self aligning, self tightening, and prevent the rollers from rotating in their frames. O-rings connect the rollers to one another and transmit power from the DRIVEROLL roller to every roller in the zone..
The ZONEXTM module, a variable output speed and torque controller, uses a potentiometer to control output torque for minimal accumulation pressure. This eliminates parts-basket collisions and subsequent damage to fragile motor components.
Because zones "sleep" once a load passes downstream, the conveyor system reduces energy consumption and noise levels. Upon receiving a load, each zone automatically turns on until the load moves downstream.
Prior to conveyor installation, a two- to three-day lag time existed between machining and washing. "Now the parts are washed within two hours of machining," says DellaVecchia.
Additional details…Contact Mike Gawinski, Interroll, 3000 Corporate Dr., Wilmington, NC 28405, (910) 799-1100.
Other Applications
• Materials handling
• Manufacturing
Amplifier protects motors for maximum output
Device safely pushes the output torque and power limits of drive components
John Lewis, Northeast Technical Editor
Pittsburgh, PA--As environmental compliance standards become more stringent, tank inspection and maintenance requires more resources. Responding to this need, RedZone Robotics Inc. has built a prototype cylindrical robot called "Fury." Designed to navigate an underground fuel tank's interior surface, Fury can measure the tank's wall thickness with an ultrasonic transducer.
Deploying a robot through a 4-inch ID pipe to inspect fuel tanks is no easy task, says RedZone engineer Frank Robb. Space constraints and harsh operating conditions limit design options. In this case, a power amplifier with Drive Protection Monitor (DPM), made by Advanced Actuators, Bradfordwoods, PA, enabled RedZone engineers to meet their high-reliability objectives. The result: maximum safe output torque and power from the drive components.
The initial wheel-drive design employed two simple power supplies with fixed current limits, providing energy for the ironless-core electric motors driving the robot's magnetic wheels.
Each magnetic wheel produces 200 lbf between the robot and the low-carbon steel plates that comprise the tank. When the robot attempted to climb over the tank's welded lap joints, the magnetic force proved to be too much for the wheel drives to overcome, says Robb.
To increase the motor's torque output, Robb considered several options. Larger motors wouldn't meet size constraints. Increasing the gear ratio between motor and drive wheel would reduce the robot's speed and increase overall inspection time. Temporarily increasing the motor's current would increase output torque, but would also risk motor damage.
"By using the PC L40 'smart' amplifiers with DPM, we got higher peak torques from the small motors," Robb explains. The DPM's ability to calculate motor winding and power amplifier transistor-junction temperature al-lows safe motor current increases. Its motor case temperature sensor provides data for calculating motor-winding temperature, even on brush-type motors where the rotating armature is not accessible.
Directly mounting the PC L40 into the 51/4-inch disk drive bay of the controlling PC eliminated the need for a separate mounting chassis. Adding the DPM required an investment of only a few percent of the total motor and amplifier cost. Users input the motor's thermal resistance and cooling time constant to the DPM. Then ambient temperature, motor current and voltage measurements are used to continuously calculate the motor's winding temperature and the semiconductor-junction temperature. If one of these values exceeds the programmable setpoint, the system shuts down.
"Other drive-component thermal-protection systems' temperature calculations don't come close to the accuracy of DPM's techniques," says engineer Bob Anticole of Advanced Actuators. For example, ignoring the motor's ambient temperature can cause ±20C error, and an additional ±20C error can arise because the thermal time constants depend on the magnitude of motor currents. Another ±50C error can result because motor heating depends on the temperature-dependent motor resistance.
"Realizing you only have 100C between a cold motor and one at its maximum limit, and the potential for error, makes me appreciate the accuracy of the DPM's temperature calculations," says Anticole. Patents are pending on the motor winding temperature and semiconductor junction sensing, as well as the programmable fuse, brush and bearing protection, power sharing, current-output drive stage, and configuration.
"If you need the maximum safe output torque and power from drive components, or cannot tolerate a failure, you need a DPM," says Anticole. If the application doesn't need maximum output from the motor and power amplifier, then oversize them. If you can tolerate a failure, replace them when they fail.
Additional details…Contact Bob Anticole, Advanced Actuators, 19 Commons Dr., Bradfordwoods, PA 15015, (412) 935-3702.
Other Applications
• Servo systems
• Industrial robots
• Film drives
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