JPS5851430A - Limit switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a limit switch used for position detection.

Conventional glue mist switches use an electrical detection method, which extracts the opening and closing of electrical contacts in a field-installed limit switch as electrical signals depending on the position of the object.

However, with this method, there was a problem of contact failure due to rust on the contacts, and conversely, there was also a problem of welding of the contacts.

In particular, when installing a limit switch in an explosive atmosphere, it is necessary to use an expensive explosion-proof type.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photodetection type limit switch that does not have the above-mentioned problems caused by conventional electrical contact type glue mint switches.

The key point of the present invention is that there is no electrical equipment on site, and light generated at a distance is supplied to an on-site limit switch through an optical fiber (bar). By returning the reflected light to a distant place through the same optical fiber and detecting this light with a photosensitive element, the position of the limit switch plunger, that is, the position of the target object, can be detected using just one optical fiber. .

The figures show specific embodiments of the present invention. The plunger 2 that moves inside the switch body is pressed against the position detection object 4 by a spring 3. The plunger has a hole 7 through which light from the input/output optical fiber 5 passes through, is reflected by a reflection plane mirror 6, and returns to the optical fiber 5 again.

Reference numeral 8 denotes a light-emitting element or other light-emitting object located far away, which is connected to the electric current 12iF10 through a wiring 9 and constantly emits light.

When the plunger is in the position shown, the light from the light emitting element 8 passes through the semi-transparent mirror 11, enters the optical fiber 5, passes through the plunger hole 7, and is reflected by the reflector 6.
The light returns through the optical fiber 5 again, is reflected by the semi-transparent mirror 11, is converted into an electrical signal by the photosensitive element 12, and is detected by the signal detector 14 through the output wiring 13.

When the plunger is pushed in a little due to the movement of the purpose object 4 and the hole 7 is removed from the position of the optical fiber, the light is blocked by the plunger and no electrical signal is detected by the detector 14.

In this way, the position of the object is known, ie the role of a limit switch is achieved.

By adopting this method, it is possible to provide a limit switch that is compact and can detect with a single optical fiber, while eliminating the disadvantages of the electric contact type limit switch mentioned above.

[Brief explanation of drawings]

The figure shows an embodiment of the invention.

Claims (1)

[Claims] 1. In a limit switch that detects whether an object is at a specified position, the object is irradiated with light from a light source via an optical fiber, and the reflected light from the object is sent back through the optical fiber to determine the position of the object. A limit switch characterized by detection.