Optical filter for protective welding lens assemblies

• US 4,728,173 A
• Filed: 02/22/1985
• Issued: 03/01/1988
• Est. Priority Date: 02/24/1984
• Status: Expired due to Fees

• Current Assignee: Esab AB (Enovis Corp.)
• Original Assignee: Peter Toth
• Inventors: Toth, Peter
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Lewis, David
• Application Number:
  US06/704,189
• Time in Patent Office: 1,103 Days
• Field of Search: 350/335, 350/337, 350/339 F, 350/349, 350/281, 350/278, 350/279, 350/283, 350/332, 219/147, 2/8
• US Class Current: 349/14
• CPC Class Codes: A61F 9/067 with variable transmission
• CPC Class Codes: G02F 1/13475 in which at least one liquid crystal cell or layer is doped with a pleochroic dye, e.g. GH-LC cell G02F1/13476 takes precedence

Abstract

An optical filter for welding protective lens assemblies has two parallel electro-optical cells, at least one of the cells being of the nematic type with admixture of dye molecules with anisotropic light absorption. The filter comprises a filter sheet disposed in the ray path of the cells and allowing transmission within a wave range which is offset with respect to the wave range within which said one cell is transmitting residual light in its absorbing state.

Claims

1. An optical filter in a protective welding lens assembly having a predetermined field of vision, comprising two parallel electro-optical cells, each of which covers substantially the entire field of vision of the protective welding lens assembly and each of which has a light transmission which is dependent on the voltage applied across two transparent electrodes included in the respective cell and having intermediate layers of liquid crystals, one of said cells being light-transmitting when voltage is applied and light-absorbing when voltage is not applied, the other of said cells being light-transmitting when substantially no voltage is applied and light-absorbing when voltage is applied, wherein at least a first of said cells is nematic with an admixture of dye molecules with anisotropic light absorption, the optical filter further comprising a contrast-enhancing filter sheet which also covers said entire field of vision of the protective welding lens assembly, said filter sheet being disposed in the ray path of the cells and allowing transmission of visible light within a wave-length range in which the first cell is absorbing light in its absorbing condition, and said filter sheet preventing transmission of light within a wavelength range within which the first cell is transmitting light in its absorbing condition, said optical filter having an electric circuit for controlling the transmission of the optical filter by selecting voltages for applying across the electro-optical cells, said electric circuit having a timing circuit for applying a voltage of a short duration which is higher than the subsequent working voltage to said other cell when the optical filter is caused to switch from the transmitting to the absorbing condition, the electric circuit further comprising a high-pass filter and a photodetector whose output serves a voltage supply for said electric circuit and, via said high-pass filter, is connected to the trigger input of the timing circuit for triggering the timing circuit when the photodetector receives light modulated by frequencies above the limit frequency of the high-pass filter.

2. An optical filter as claimed in claim 1, wherein the filter sheet is arranged on the light-exit side of the first cell.

3. An optical filter as claimed in claim 1, wherein the first cell is arranged on the light-exit side of the second cell for receiving plane-polarized light therefrom.

4. An optical filter as claimed in claim 1, wherein the other cell is nematic without admixture of dye molecules with anisotropic light absorption and on either side of the transparent electrodes has a polarizing filter.

5. An optical filter as claimed in claim 1, wherein both electro-optical cells are nematic with admixture of dye molecules with anisotropic light absorption.

6. An optical filter as claimed in claim 1, further comprising battery means serving as a voltage supply for said electric circuit, and means responsive to the output of said photodetector for disconnecting said battery means from said electric circuit.