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Analysis of working principle and common quality problems of automatic dry-hand dryer
Nov 27, 2017

1 Introduction

After washing your hands, extend your hand to the air dryer near the automatic dry hand dryer. There will be a (hot) wind blowing the hand drying, once the hands in the process of leaving, the automatic dryer will quickly stop working, and once the continuous work for a period of time, the automatic dryer will also stop working, later try again, will continue to work. Because of the health and convenience of automatic hand dryer, more and more public places began to use automatic dryer, some families also began to use automatic hand dryer. According to the speed of the hair dryer, the automatic dryer can be divided into two types: slow and fast, according to the installation mode, the automatic dryer can be divided into two types: wall-mounted and standing vertical.

2 Working principle

Automatic hand dryer by far infrared automatic induction work, working principle as shown in the diagram, by the infrared transmitter, receiver, single steady-state delay switch, solid state relays and hair dryer, composed of simple self-excited harmonic oscillator, from the infrared emission tube emitting a frequency of about 40kHz modulated infrared light. When the hands are stretched below the automatic dryer, the emitted infrared ray is reflected back to a part of the human hand, and by the photosensitive transistor after receiving, converted to the same frequency of electrical signals, and then by infrared receiver dedicated preamplifier amplifier, shaping, band-pass comparison, output low level pulse signal, and then trigger the single steady-state circuit into the transient state , so that its output high level, light-emitting, AC solid-state relay conduction, so that the hair dryer can send hot air. When the hand dries away, loses the infrared pulse signal, restores the high level, the single steady-state circuit quickly resets, because of the delay effect, the hair dryer works 10s or so to restore automatically, thus stops the work. To adjust the movement sensitivity of the automatic dry hand, in the circuit can be added resistor and capacitance of the serial network to improve the frequency characteristics and gain of preamplifier, to ensure that in the presence of a temporary signal disappeared such as shaking the hands of the infrared detection range, the circuit will not be instantaneous jump, to ensure that the hair dryer can still be stable, continuous work.

3 Key Components

The "Heart" of the automatic hand dryer is mainly a single dissimilar motor driving the wind vane, considering that the automatic dryer is used in the moist environment with water source, the structure of the motor must be adapted to the damp environment without the early failure phenomenon. such as single-phase capacitor asynchronous motor, often due to capacitance failure caused by the humid environment of capacitive induction motor operating reliability of the reduction. such as the use of Single-Phase series of motor, damp environment in the work of the commutator easy to damp short-circuit, dielectric insulation performance of the poor, resulting in motor durability and shorten the service life. The noise of the motor is bigger, the interference of the radio waves is serious, the image of the TV set and the recording like equipment in each room and in the vicinity of it will appear many horizontal bar interference, and it is unfavorable to use. Single-phase dual-ring shaded-pole asynchronous motor is more suitable for the above environment it excludes the disadvantages of the two motors, the durability of the shaded pole motor in the humid environment has good service life long motor stator magnetic extremely loading and unloading type, the excitation winding is concentrated winding, Directly around the nylon coil rack in the core magnetic pole and then use a special fixture to the core of the magnetic pole pressure in the choke part of the work on the 49kV pressure machine to complete. The electrical strength of this motor structure is greater than that of the 4000v.1min not penetrate the safety technical standard of gb4706.1-2005 household appliances, electrical strength of type II electrical products 3000V. 1min does not penetrate the requirements of the normal, generally at the rated voltage on the smooth start, Compared with the rated voltage should be able to start the specified value of a greater safety margin.

4 Common quality problems

Since the automatic hand dryer sales are small, large enterprises are unwilling to organize production, so that the current domestic automatic hand-dryer manufacturers are generally some production scale, poor technical strength, production equipment, small enterprises, and even there are some hand-workshop-type processing plants, the production of these enterprises are worrying about the quality of products, In recent years, the pass rate of automatic dry hand type test is less than 50%, and the following quality problems exist mainly:

4.1 Incomplete or nonstandard product markings

Marking should contain important information that guides the user to use correctly, and marking the product correctly is one of the basic measures to ensure the safety of users ' personal property. Marking requirements durable and eye-catching, after normal use should not fall off, the content should be clearly discernible. The common problem is no manufacturer name, model type, no waterproof grade mark, no assembly drawing, manual, ii apparatus logo nonstandard, rated voltage, power sign is not standard, logo is not congruent.

4.2 Electrical Safety can be more problematic

Exaggeration of technical indicators, deception and misleading of consumers (mainly concentrated in one-sided exaggerated input power), internal wiring disorder, grounding connection unreliable, heat and flame resistance test unqualified and electric shock protection is unqualified, these unqualified projects are closely related to the user's personal safety and environmental safety of the mandatory project. These products are not qualified mainly because of the small scale of production enterprises, weak technical strength, resulting in the production of electric components in the parameters of the design error, resulting in excessive input power deviation, the outlet openings are too large, leading to some products with testing means to be able to contact the charged body. Some internal wiring using a simple solder connection to the use of wire leads to unreliable connection, the selection of insulating materials do not have to withstand 125 ℃ heat-resistant properties of poor materials. Some enterprises lack of necessary detection means, a few enterprises on product quality control is not strict.

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