Rotary Temperature Transmitter for Godet Rolls: Temperature Control is Critical to Quality Control
In the manufacturing of synthetic fibers, the yarn is drawn, or stretched, between rotating hubs called godet rolls. Stretching the yarn changes its mechanical properties (strength, flexibility, texture, even color). Heat is applied to the yarn by the godet rolls. The heating of the stretched fiber "sets" the mechanical properties of the yarn. The combination of stretching and heating the yarn produces the desired product quality. Consistent temperature control on the godets is critical to producing consistent product quality.
Controlling Godet Temperature
To control the temperature on the godet roll and get consistent product quality requires accurately measuring the roll temperature. A feedback control scheme is used to operate the duty cycle of the heater (typically a stationary induction heater mounted inside the hollow godet roll shell). Several different methods can be employed to measure the temperature on the rotating roll shell and provide it to the heater controller.
The simplest method uses a stationary sensor that is hard wired to the heater controller. The stationary sensor is placed close to the rotating roll, often in a groove in the roll, and senses the ambient temperature adjacent to the roll, which approximates the temperature on the roll. Although this method is simple and inexpensive, it is limited in accuracy.
Infrared technology is another option that can be employed to read the temperature on the rotating roll. This method is also limited in accuracy due to the fact that it is dependent on surface color which may change with heat and the introduction of finish chemicals from the yarn.
The most accurate way to measure the roll shell temperature is to place a sensor on the rotating roll, embedded in the roll shell just beneath the surface where the yarn is being wrapped. To monitor the rotating sensor an extremely accurate telemetering system is required to transmit the sensor data from the rotating roll shell to the stationary control system. These telemetering systems are commonly referred to as rotary temperature transmitters.
How A Rotary Transmitter Works
The rotary temperature transmitter is mounted on the rear end of the roll motor(a hollow shaft is utilized to wire the sensor from the roll shell mounted on the front end of the motor). A stationary pickup adjacent to the rotating transmitter couples power to it. The rotating transmitter powers the temperature sensor and monitors its output. The transmitter converts the sensor output to a transmittable signal and sends it out to the stationary pickup which processes it and sends information to the heater control circuit.
An adjustable set point on the heater controller, incorporated with the feedback signal from the rotary transmitter, allows the godet roll to be operated precisely at the critical temperature. Consistent, precise godet temperature produces consistent, superior fiber. Obviously, a critical requirement in this process is accurate, linear, repeatable transmitting of the sensor information. Variation or drift in the transmitter signal creates unacceptable variations in the fiber.
Technology Improvements
Moving the technology forward from utilizing a stationary sensor adjacent to the roll, to a rotating sensor embedded directly under the fiber wrap is a quantum leap in process control. One method utilized to couple the rotating sensor is an obvious choice, the slip ring. A slip ring is a mechanical device where a stationary conductive brush rides on a conductive rotating ring, acting as a path for current flow. Mechanical wear, combined with the harsh operating environment and high rotating speeds of synthetic fiber production significantly limit the signal quality and life of these mechanical devices, making the slip ring a poor choice for these applications.
Non-contact systems are better suited to the fiber industry. But non-contact systems that require precise positioning between rotating and stationary sections make them burdensome to install and calibrate. These systems are also vulnerable to damage from loose or failing motor bearings.
Improved power/data transmission technologies eliminate the need for close tolerances by incorporating miniature electronic circuits. However, electronics exposed to the temperature environment of the fiber plant are susceptible to drift. One pioneer in the industry actually incorporated tiny "ovens" to house the electronics in an elevated (consistent) temperature environment for stability.
Temperature compensated circuits and today's temperature stable components moved the technology forward, effectively eliminating circuit drift and allowing even more sophisticated electronic designs. Inductive and capacitive power schemes employed in conjunction with inductive, capacitive and even optical data transmission techniques (susceptible to degradation from industrial grime) are used in various combinations. Some systems incorporate sensor data linearization at the transmitter (preferred), others linearize at the heater control circuit.
Binsfeld Engineering Inc. - Leading Technology in Rotating Sensor Data
Binsfeld Engineering Incorporated offers a unique opportunity to the fiber industry in that its primary business is rotating data transmission. Machinery manufactures have a much broader focus and may mistakenly consider the rotary transmitter a minor detail. Incorporated in 1978, BEI began as a consulting business performing mechanical testing on manufacturing machines. In 1984 the business expanded when it introduced its product line of miniature, battery powered, radio telemetry transmitters designed to strap onto machine shafts and transmit torque sensor data.
In 1990 a major fiber producer contacted BEI to design a permanently powered temperature transmitter for reading temperature sensors on rotating godet rolls. Binsfeld Engineering now produces a variety of rotary temperature transmitters for the fiber industry, including its latest designs, which incorporate microprocessor technology for state-of-the-art temperature control. In addition to high precision and immunity to temperature drift, the microprocessor-based designs offer flexible outputs that can be tailored to match nonlinear control schemes of older, existing machinery. This flexibility allows even older machines to be upgraded to produce significantly superior fiber.
Binsfeld Engineering Incorporated, 4571 West MacFarlane Road, Maple City, MI 49664. Tel: 231-334-4383; Fax: 231-334-4903.