1. Field of the Invention
The present disclosure is related to measuring an aspect of a load supported by a container. More particularly, the present disclosure is related to measuring a size of a load in a tub or basket that is subject to a rotational acceleration.
2. Description of Related Art
Vertical axis washing machines, also known as top loading washing machines, represent a large portion of the overall washing machine consumer market in the United States. Horizontal axis washing machines represent a smaller segment of the United State market and abroad typically represent a larger portion of the overall washing machine consumer market.
Most vertical and horizontal axis washing machines include a spin cycle for removing water and/or detergents from the laundry using centrifugal force and spinning a wash load tub, also referred to as a laundry tub (“tub”) or basket. During a typical spin cycle, the motor, typically an induction motor, of the washing machine spins the tub at relatively high speed(s).
Historically induction motors used in washers have been single phase induction motors or PSC induction motors. More recently 3-phase induction motors, have been used in some commercially available washers. The 3-phase motors in washers for home use are typically powered by standard single phase AC household electric power. As part of a 3-phase induction motor washing machine, a circuit associated with the motor converts the single phase AC household electric power to three phase power; the three phase power is better at motor starting and operates more efficiently than single phase power.
A simplified explanation of an induction motor, ignoring losses follows: The induction motor has a rotor with a short-circuited winding inside a stator with a rotating magnetic field. The flux from the rotating field induces a current flow in the rotor. The frequency of the current flowing is equal to the difference between the rotational speed of the stator field and the rotational speed of the rotor. This difference in speed, or frequency, of the stator magnetic field and the rotor magnetic field is known as the slip.
The rotor current causes a rotor magnetic field, which is spinning relative to the rotor at the slip frequency and relative to the stator, at the stator applied frequency. The interaction between rotor magnetic field and the stator magnetic field generates a torque in the rotor.
A washing machine wash cycle has various modes such as fill, drain and spin, agitation, and spin. Load sensing can occur before, during or after various segments of the wash cycle. Knowing the amounts of water and detergent used in the wash cycle can be helpful in providing an efficiently run washing machine.
The weight of a load of clothes loaded into a clothes washer for washing is an important parameter in determining the proper amount of water and detergent to be used for the wash cycle. Large clothes loads require larger quantities of water than do small loads. Better clothes washability and significant water and energy savings can be achieved when the proper amount of water is filled into the washer tub for a given clothes load. Too much water or detergent is wasteful, and too little of either will generally adversely affect the effectiveness of the washing, and may result in increased energy consumption due to a higher load on the motor as a result of the inability of the clothes to move freely in the water. Additionally, load size may aid in determination of max spin speed and degree of load imbalance. For example, a 1 lb. load with 0.5 lb. imbalance may be more severe than a 10 lb. load with 0.5 lb. imbalance.
Techniques or methods of estimation of the load of clothes loaded into a washer employed by the washer itself are desirable in that it eliminates guesswork on the part of the machine operator which can lead to improper water fill or use of an improper amount of detergent. Knowing load size can also prevent damage to the washer by limiting max speed. Prior art techniques include displacement sensors mounted at tub springs; magnet and coil pickup sensing relative displacement of tub from chassis; and ultrasonic transducers. Prior art washing machines that use sensing hardware are costly due to the need for dedicated sensing hardware.
Another technique involves determining a load size by measuring a time required for a load to change speed when a known stimulus is applied such as a positive speed step or coasting. While suitable for its intended purposes, this method is not particularly suitable for horizontal axis washers that have two main sources of friction.
A first source of friction in a horizontal axis washer involves clothes rubbing against a door and/or a window of the washer. As the clothes spin around in the machine, they rub against the window causing friction. This friction increases as more clothes are added to the load.
A second source of friction (and a major source in a vertical axis washer) involves machine friction that is caused by bearings, belt tension and other variables of the washer. Machine friction may also change over time as the belt tension weakens or the bearings begin to wear out.
Accordingly, there is a need for a washing machine that overcomes, alleviates, and/or mitigates one or more of the aforementioned and other deleterious effects of prior art washing machines.