解決方案

何謂緊急停止開關 | 台灣

在用於工廠等處的機械設備，有搭載為確保作業員安全，能讓機械設備緊急停止動作的「緊急停止系統」【圖1】。
做為此系統的輸入部份而設置的零件就是緊急停止開關。當作業員感到危險或是機械設備發生異常時，能以手動進行操作的開關【圖2】。

緊急停止開關的構造

按鈕顏色與形狀

在機械設備的操作面板上，通常會排列著許多的操作按鈕或儀表。
緊急停止開關在這些元件當中，在緊急時也必須要能立即被辨識出來。因此，緊急停止開關的操作按鈕外觀被要求設計為大顆的、紅色的，且用手掌容易按壓的蘑菇頭造型。此外，還需將開關的周邊以黄色進行搭配使緊急停止開關更加醒目【圖3】。

NC（Normal Close：常閉）型的輸出接點

開關的接點可以分為Normal Open（NO：常開）型與Normal Close（NC：常閉）型兩種（圖4）。
而緊急停止開關，被要求一定要使用NC型的接點（NC接點）。其理由說明如下。

使用NO型的接點(NO接點)，雖然在未按下按鈕時(非緊急狀態)接點為開路狀態，所以包含緊急停止開關的回路之電流並不導通，只有在按下按鈕將接點閉合後通知緊急狀態的電流才會導通至回路當中。但是，如果接點有異物附著或是配線發生斷線，那麼回路就會因為電流無法導通而導致機械設備無法被緊急停止。這種情況被稱為危險側故障。

另一方面，NC接點則是在未按壓按鈕時接點為閉合狀態。藉由利用這種特徴，讓意味著安全狀態的電流導通至回路中。當按下按鈕使接點斷開時，電流會被遮斷，並使機械設備停止。也就是說，由緊急停止開關所傳導出的緊急停止信號，會將原本導通(意味著回路為安全狀態)的電流進行遮斷而形成緊急停止輸出。

當接點發生異物附著或者配線被切斷等情形也會被判斷為緊急事態，機械設備也會被停止。這種情形被稱為安全側故障。國際安規上要求像這種與安全相關的控制系統或零件因自身發生故障時，必須使機械能以安全停止的方式形成故障。

Direct Opening Action

The direct opening action is a function that ensures that the force of pressing the button is reliably transmitted as the force to open the NC contact.
Even if the contact is welded (A state where the contact surface melts and then cools and adheres due to an inrush current exceeding the capacity during contact opening and closing) shut, the NC contact can be opened reliably by pushing the button.
For this reason, everything from the operation buttons to the contacts must be made of rigid and solid parts, as shown in the right figure in Figure 4.
It is not possible to transmit the force that presses the button using resilient components such as springs along the transmission path. This is because if an resilient component such as a spring is damaged, the NC contact cannot be opened by pressing the button.

Latching Mechanism (Self-holding Mechanism)

In general, emergency stop switches are activated in case of emergency, and so when the button is pressed, the NC contact opens to interrupt the current, and at the same time, a latching mechanism is activated to hold the button in the pressed-down position. This allows the current interruption state to be maintained, thus preventing unintended restarting of machinery and equipment.
After confirming safety, there are two ways to release the latch and return the button to its original position: by turning the button in a specified direction (turn-reset type) or by pulling the button back to its original position (pull-reset type). The prevailing reset type varies by the region. For this reason, there are dual-purpose types that can be reset by both turn and pull reset for enabling use in any region (Figure 5).

Product Descriptions of X Series Emergency Stop Switches

Required Installation Location

The standards require that emergency stop switches be installed in the following locations in machinery and equipment.

● Locations required as a result of risk assessment
● On each operation panel (except when not required as a result of risk assessment)
● At the entrance and exit of machinery and equipment
● Locations where operator intervention is needed to operate the machine, such as hold-to-run control functions and enable control functions
● All locations where intervention between the operator and the machine is expected, such as workpiece loading/unloading ports