In the previous article, various switches were classified according to their construction and use. This article will introduce the representative of the detection switch - micro switch (Figure 1). The micro switch is classified as a detection switch according to the purpose, but is sometimes used as an operation switch. Microswitches include a wide range of products of varying sizes and are used in many devices. 
Figure 1: Microswitch
Definition of micro switch
The micro switch is defined by the Japan Electronic Control Equipment Industry Association (NECA) as follows.
The Snap Action mechanism has a small contact spacing and a snap action mechanism, and covers a contact mechanism that performs a switching operation with a predetermined action and force, and has an external actuator and a small outer shape.
The quick acting mechanism refers to a mechanical mechanism that instantaneously switches the contact at a specific operating position regardless of the operating speed. The switch that uses this mechanism to operate with a predetermined action and force is a micro switch.
Characteristics
<Small size but can switch large current>
Under normal circumstances, when the electronic circuit is turned off, a spark called arc is generated between the contacts. The larger the current, the easier it is to generate an arc. The slower the speed of switching the contact, the longer the duration of the arc is, which is the factor that causes the contact to deteriorate. The quick-action mechanism of the micro-switch can instantly switch the contact point, so the arc duration is short, and the size is small, but it can be used for a circuit with a large current.
<High precision>
The micro switch can basically switch the contact at the same position even if the opening/closing operation is repeated repeatedly, so the position detection error is small, and it is suitable for applications requiring high precision. This is also a unique advantage of the micro switch with a snap action mechanism.
<Durability>
Since the duration of the arc is short, the damage to the joint is also small, so the durability is improved.
<Touch and sound>
The snap action mechanism has a unique touch and sound during operation, so the operation can be confirmed by tactile and audible.
species
The size of the micro switch is divided into four types: normal type, small size, ultra small size and extremely small size. (figure 2). Ordinary microswitches are used in large-scale industrial machinery and equipment, and small, ultra-small and ultra-small micro-switches are used in business equipment and home appliances.
It can also be classified according to environmental resistance. For example, it includes a type that has a sealing function (sealed type) and a type that does not have a type (normal type).
Figure 2: Types of microswitches (click to enlarge)
structure
The construction of the micro switch is shown in Figure 3. The main components are (1) actuator unit, (2) snap mechanism unit, (3) contact unit, (4) terminal unit, and (5) outer casing. Let's introduce it in order.
Figure 3: Construction of the microswitch (click to enlarge)
(1) Actuator section
It is used to transmit external forces and actions such as the operating body to the internal mechanism. Different types of actuators are used depending on the shape and action of the operating body. Representative actuator shapes include a Pin Plunger, a Hinge lever, a Hinge roller lever, and the like (Fig. 4). The needle plunger type is used for position detection of short stroke products with high precision. The hinge rod type has a high degree of freedom due to the large stroke that can be used for a wide range of applications. The roller hinge type is suitable for detecting high speed running cams and the like.
Figure 4: Main shape of the actuator
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