Detection of LED contamination

Abstract

Device for detecting the degree of pollution with a transparent cover (4) of a circuit board (2) with LED spotlights (3), wherein the LED spotlights (3) are cooled individually or in groups by cooling devices (5) and the device has electronics for detecting temperatures, wherein temperatures of the LED spotlights are detected directly or indirectly by the electronics and wherein the electronics infer the contamination of the transparent cover (4) from the comparison of the temperatures among each other and wherein the electronics detect the temperatures of the cooling devices (5) associated with the LED spotlights (3), characterized by the fact that an average value is calculated from the temperatures of all cooling devices (5), whereby a threshold temperature value is determined on the basis of this average value which may not be exceeded by any cooling device (5), and that an LED spotlight (3) is automatically switched off as soon as the temperature of the associated cooling device (5) reaches a specified threshold temperature value.

Description

[0001] LED-UV dryers are used for curing UV ink or UV varnish, especially when printing sheets and three-dimensional components made of any material with inkjet or offset printing presses.

[0002] German patent DE 10 2009 007 873 A1 describes such an LED dryer for curing UV-cured ink for printing presses. In this device, LEDs are arranged in rows perpendicular to the transport direction of the substrate on a carrier.

[0003] WO 2011 / 031529 A2 describes a device for protecting LEDs from contamination. The LEDs are housed in a casing which has a transparent cover in the UV radiation exit area.

[0004] German patent DE 10 2013 019 814 A1 discloses a device that can determine the degree of soiling of a transparent cover of such an LED module. Temperature measurements are taken at one or more locations on the cover using additional sensors. The degree of soiling of the cover can then be derived from the measured values. If the soiling is too high, the LED UV dryer is switched off.

[0005] Patent application US 20120062667 A1 discloses a hardening device in a printing press, which is composed of four substations. These substations have one or more LED areas, whereby the LEDs in the LED areas can be individually controlled.

[0006] The problem that arises in practice with such lamps is that dirt on the transparent covers reflects the UV light. This leads to temperature differences within the lens and thus to stress. If the temperature differences are too great, the cover can break. The more dirty a lens is, the more radiation is reflected.

[0007] The object of the present invention is to create a device that determines the degree of soiling of the transparent cover without using additional sensors to measure the temperature of the cover itself.

[0008] This problem is solved by a device having the features of claim 1. Advantageous embodiments are described in the dependent claims.

[0009] The device according to the invention for detecting the degree of soiling of a transparent cover of a circuit board with LED emitters provides that the emitters are cooled individually or in groups. The temperatures of the individual or grouped cooling devices or the temperatures of the LED emitters are detected directly or indirectly, and soiling is inferred from a comparison of these temperatures. Indirect detection is achieved, for example, via temperature sensors on the cooling devices. Direct detection is achieved, for example, via temperature sensors on the LED emitters.

[0010] A first advantageous embodiment of the invention provides that the LED spotlights can be switched on and off independently of each other.

[0011] According to the invention, an average temperature is calculated from the temperatures of all cooling devices or LED spotlights. Based on this average, a threshold temperature is then determined, which none of the cooling devices or LED spotlights may exceed. This threshold is chosen such that it lies below the critical temperature difference between the average temperature of the LED spotlights and that of a single LED spotlight, which would cause the transparent cover to break.

[0012] Furthermore, it is in accordance with the invention that those LED spotlights whose associated cooling device has reached this threshold temperature are automatically switched off in order to ensure that the threshold temperature is not exceeded.

[0013] A further advantageous embodiment of the invention provides that an optical output device is associated with the circuit board containing the LED emitters. Additionally, a threshold temperature value is defined for the average temperature of the LED emitters. This threshold temperature value corresponds to a critical degree of contamination of the entire transparent cover. If the threshold value is reached, the optical output device indicates that the transparent cover must be cleaned or replaced.

[0014] The described device and further developments according to the invention can be seen in the following exemplary embodiment and in the drawings.

[0015] The figure shows a section of a printing press. Visible is the underside of a circuit board with LED spotlights and a transparent cover, which shows signs of soiling.

[0016] The circuit board 2 in the printing press 1 has several LED spotlights 3, each with its own cooling unit 5. A transparent cover 4 is located in the UV radiation exit area. The temperature of the cooling units 5 is continuously monitored by an electronic control unit 8, which is connected to the control system of the printing press 1 and an optical output device 6. An average value is calculated from the measurements. Based on this average value, a threshold value is continuously determined. This threshold is lower than the temperature difference between the average temperature and the temperature that an individual cooling unit would have to reach to cause the transparent cover to break. A threshold value for the average temperature is also defined. If this threshold is reached, it means that the transparent cover 4 is heavily soiled and must be cleaned or replaced.Initially, the transparent cover 4 is clean. The temperature of all cooling units 5 is the same. During the printing process, contaminants 7 accumulate on the transparent cover. These reflect the UV radiation emitted by the LED lights 3. This heats up individual lights 3. This also leads to a temperature increase in the cooling units 5 associated with the lights 3. The average temperature of the cooling units 5 rises. A particularly large amount of contaminants 7 has accumulated under one light 3. A particularly large amount of radiation is reflected onto it. The temperature of its cooling unit reaches the threshold value, which represents the maximum permissible difference from the average temperature. The light 3 is then automatically switched off. An optical output device 6 indicates to the operator when the permissible temperature threshold is exceeded. Reference symbol list 1 printing press 2 circuit boards 3 LED spotlights 4 transparent covers 5 Cooling unit 6 optical output device 7 Contaminations

Claims

[1] Device for detecting the degree of pollution with a transparent cover (4) of a circuit board (2) with LED spotlights (3), wherein the LED spotlights (3) are cooled individually or in groups by cooling devices (5) and the device has electronics for detecting temperatures, wherein temperatures of the LED spotlights are detected directly or indirectly by the electronics and wherein the electronics infer the contamination of the transparent cover (4) from the comparison of the temperatures among each other and wherein the electronics detect the temperatures of the cooling devices (5) associated with the LED spotlights (3), characterized by , that an average value is calculated from the temperatures of all cooling devices (5), whereby a threshold temperature value is determined on the basis of this average value which may not be exceeded by any cooling device (5), and that an LED spotlight (3) is automatically switched off as soon as the temperature of the associated cooling device (5) reaches a specified threshold temperature value. [2] Device according to claim 1, characterized by that the LED spotlights (3) can be switched on and off independently of each other. [3] Device according to any one of the preceding claims, characterized by , that the circuit board (2) with LED spotlights (3) is associated with an optical output device (6), wherein a warning about the contamination of the transparent cover (4) is displayed on this optical output device (6) as soon as the average temperature of the LED spotlights (3) reaches a specified threshold. [4] Inkjet printing machine with an LED-UV drying unit and a device according to claims 1 to 3 for monitoring the contamination in the LED-UV drying unit. [5] Offset printing press with an LED-UV drying unit and a device according to claims 1 to 3 for monitoring the contamination in the LED-UV drying unit.

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