1. Field of the Invention
The invention relates generally to automatic drying of synthetic fabric loads and more particularly to detecting a synthetic fabric load in an automatic dryer.
2. Description of the Related Art
Dryers are well-known appliances for drying clothing and other fabric items, such as towels, sheets, blankets, and the like. Most dryers comprise a rotating drum sized to receive a load of fabric items, a blower for forcing air through the drum, and a heater to heat the air as it flows through the dryer. Typically, dryers can be operated in a manual mode, wherein the user inputs a desired drying duration, or an automatic mode. In the automatic mode, the user enters inputs, such as fabric type (e.g., normal, permanent press, and delicate) and a desired dryness level (e.g., more, normal, and less), and a controller in the dryer runs a drying cycle according to the inputs. To ascertain the dryness level or, conversely, moisture content of the fabric items during the automatic mode, the dryer usually comprises a moisture sensor in the drum so that the fabric items contact the sensor as the drum rotates. An example of a moisture sensor is a pair of spaced electrodes on the interior surface of the drum. When a moist fabric item simultaneously contacts both sensors during what is commonly termed a “wet hit,” the electrical circuit is completed, and the sensor sends a signal to the controller indicating that the fabric items are moist. The quantity of wet hits within a specified time period is translated into the moisture content of the fabric items, and the moisture content is monitored until the number of wet hits falls below a predetermined threshold value determined by the desired dryness level input by the user. When the number of wet hits is below the threshold value, the controller determines that the fabric items have achieved the desired dryness level or that the drum is empty, and the heating portion of the drying cycle ceases.
Automatic drying of fabric items is effective and efficient when the fabric items are comprised of natural fabrics, such as cotton. These fabrics dry evenly from the interior to the outer surfaces thereof, and, therefore, moisture sensors, which contact the outer surfaces of the fabric, can successfully detect the moisture content of the fabric items. Synthetic fabrics, however, can be problematic for conventional moisture sensors and are consequently difficult to dry during automatic drying cycles. During the initial stages of drying cycles, water tends to gravitate toward the interior of synthetic fabrics to leave the outer surfaces relatively dry. As a result, the synthetic fabrics with the dry outer surfaces do not register a wet hit on the moisture sensors even though the interior of the fabric can be moist. Consequently, the controller incorrectly deduces that the load has achieved the desired dryness level or that the drum is empty and prematurely terminates the automatic drying cycle. Thus, it is desirable for the automatic dryer to be able to detect the presence of a synthetic fabric load in order to execute a proper drying cycle.