System and method for detecting defective ultraviolet irradiation light emitting diodes in a printer

Abstract

Printing system (100), comprising: a plurality of printheads (118), each printhead (118) of the plurality of printheads being configured to eject a marking material; an element (116) having a first end and a second end, wherein the plurality of printheads (118) are positioned between the first and second ends of the element (116); a holder (108) configured to hold an object (104) and move along the element (116) between the first and second ends of the element (116); a first actuator (128) operatively connected to the holder (108) to enable the actuator (128) to move the holder (108) along the member (116) and move the object (104) past the printheads (118) to receive marking material from the printheads (118) of the plurality of printheads; an ultraviolet (UV) curing device (120) having a plurality of UV light emitting diodes (LEDs), each UV LED in the UV curing device (120) being configured to emit UV light, wherein the UV curing device (120) is positioned between the plurality of print heads (118) and the second end of the member (116) to enable the UV curing device (120) to cure UV marking material ejected onto the object (104) after the object (104) has passed the plurality of print heads (118); a second actuator (138) operatively connected to the UV curing device (120); a UV detector (142) having a plurality of UV sensors and unbroken partitions (328) between adjacent UV sensors to shield the individual UV sensors from UV radiation produced by UV LEDs that are not directly opposite a particular UV sensor, each UV sensor being configured to receive UV light from one of the UV LEDs in the UV detector (142) and generate an electrical signal corresponding to an intensity of the UV light received at the UV sensor; and a controller (124) operatively connected to the plurality of printheads (118), the first actuator (128), the second actuator (138), the UV curing device (120), and the UV detector (142), the controller (124) being configured to actuate the first actuator (128) to move the holder (108) and the object (104) along the element (116) in a process direction and to enable the plurality of print heads (118) to eject marking material onto the object (104) as the object (104) has passed the print heads (118) in the plurality of print heads, and to control the UV curing device (120) to direct UV light onto the UV detector (142), to receive the electrical signals generated by the UV sensors in the UV detector (142), and to detect any UV LEDs in the UV curing device (120) that do not emit UV light at at least a predetermined intensity, by comparing a voltage of each electrical signal received by the UV sensors in the UV detector (142) with a predetermined voltage level corresponding to the predetermined intensity, detecting the UV LEDs that do not emit UV light with at least the predetermined intensity, and actuate the second actuator (138) to move the UV curing device (120) transversely to the process direction over a predetermined distance to enable a functioning UV LED in the UV curing device (120) to emit UV light onto a region of the object (104) in the holder (108) that has been opposite a UV LED that was identified as not emitting UV light at least at the predetermined intensity.

Description

FIELD OF TECHNOLOGY

[0001] The invention relates generally to a system for printing three-dimensional (3D) objects, and more particularly to systems that print objects with inks that are ultraviolet (UV) curable. BACKGROUND

[0002] Commercial printing of items typically occurs during the manufacturing process. For example, the outer skins of balls are printed with patterns or logos before the ball is finished and inflated. As a result, a non-manufacturing facility, such as a distribution site or retail store, in a region where potential customers support multiple professional, amateur, or collegiate teams must maintain an inventory of products bearing the logos of various teams that have supporters in the area. Ordering the correct number of products for the different logos to maintain inventory can be problematic.

[0003] One way to address this problem at points of sale where production is not taking place is to keep blank versions of the products on hand and print them with the designs or logos at the distribution location or retail store. Printers called direct-to-object (DTO) printers are designed to print on individual objects. Some of these printers use UV-curable inks to form ink images on the objects. UV-curable inks require a UV radiation source that shines UV light directly onto the inks on the object's surface. This light cures the inks and helps eliminate fumes that would otherwise escape from the inks. Some of these fumes can be harmful to humans.

[0004] UV-emitting light-emitting diodes (LEDs) are an effective form of UV radiation source. These semiconductor devices produce light in the UV region of the light spectrum in response to the application of a DC voltage across the semiconductor junction within the device. Typically, these UV LEDs are arranged as an array of LEDs extending cross-process, or print, direction—that is, perpendicular to the path in which the fixture and object move past one or more inkjet printheads. As used in this document, "process direction" refers to the direction of movement of an object past the printheads in a printer, and "cross-process direction" refers to an axis perpendicular to the process direction in a plane parallel to the plane in which the fixture and object move.Over the course of their operating life, some of the UV LEDs begin to emit radiation at lower intensity until they no longer emit UV light at an intensity sufficient to cure UV inks. Detecting this weakening of UV LEDs in a printer before they become completely ineffective for curing UV inks would be beneficial.

[0005] Patent application US 2012 / 0 139 993 A1 discloses a recording apparatus comprising a recording head that dispenses UV ink onto a recording material, and an ultraviolet light irradiation unit that irradiates the dispensed UV ink with ultraviolet light to cure the UV ink; further comprising a fault diagnosis unit that diagnoses a fault condition of the ultraviolet light irradiation unit, and a controller that controls the operation of the recording head, the ultraviolet light irradiation unit, and the fault diagnosis unit.

[0006] Patent application US 2005 / 0 168 509 A1 discloses an image recording device having a recording head that ejects a photocurable ink cured by photoradiation. The image recording device further includes a plurality of light irradiation devices that irradiate the photocurable ink on a recording medium and a detector that detects an illumination intensity from each of the light irradiation devices. A controller controls an energy of the photocurable ink irradiation in accordance with a detected illumination intensity.

[0007] Patent application US 2010 / 0 225 720 A1 discloses a drawing device comprising a carriage, a base configured and arranged to mount a substrate, and a moving device configured and arranged to move the substrate and the carriage relative to each other in a first direction and a second direction intersecting the first direction. The carriage includes a plurality of types of droplet ejection head units and a plurality of ink-curing light irradiation sections. SUMMARY

[0008] The invention claims a printing system according to claim 1. The printing system includes a detector configured to detect defective UV LEDs in a printer that ejects UV-curable inks to form ink images.The printing system comprises: a plurality of printheads, each of the plurality of printheads configured to eject marking material; an ultraviolet (UV) curing device having a plurality of UV light emitting diodes (LEDs), each UV LED in the UV curing device configured to emit UV light, the UV curing device being positioned to cure UV marking material after at least one of the printheads has ejected UV marking material onto a surface; a UV detector having a plurality of UV sensors, each UV sensor configured to receive UV light from one of the UV LEDs in the UV detector and generate an electrical signal corresponding to an intensity of the UV light received at the UV sensor; and a controller operatively connected to the plurality of printheads, the UV curing device, and the UV detector.The controller is designed to control the UV curing device, to direct UV light onto the UV detector, to receive the electrical signals generated by the UV sensors in the UV detector, and to detect any UV LEDs in the UV curing device that are not emitting UV light at least at a predetermined intensity.

[0009] The invention also claims a method of operating the printing system according to claim 6. The method of operating the printing system with a detector configured to detect defective UV LEDs helps ensure that UV-curable ink images are properly cured before the image exits the printer.The method includes actuating, by a controller, an ultraviolet (UV) curing device to direct UV light into a UV detector, the UV curing device having a plurality of UV light emitting diodes (LEDs) and the UV detector having a plurality of UV sensors, each UV LED in the UV curing device being configured to emit UV light and each UV sensor being configured to receive UV light from one of the UV LEDs in the UV curing device and generate an electrical signal corresponding to an intensity of the UV light received at the UV sensor, receiving, by the controller, electrical signals generated by the UV sensors in the UV detector, and detecting, by the controller, any UV LEDs in the UV curing device that do not emit UV light at at least a predetermined intensity. SHORT DESCRIPTION OF THE DRAWINGS:

[0010] The above aspects and other features of a printing system that detects defective UV LEDs in the printer are explained in the following description in conjunction with the accompanying drawings. Fig. Figure 1A is a side view sketch of a printing system with a detector that detects defective UV LEDs in an array of UV LEDs in the printer. Fig. Figure 1B is a frontal perspective of the bracket in the system of Fig. 1A. Fig. Figure 2A is a graph showing the response of a UV sensor to increasing intensity of UV radiation at different temperatures, and Fig. Figure 2B is a graph showing the spectral sensitivity of the UV sensor. Fig. Figure 3 is a block diagram showing the structure of the UV LED array and the structure of the UV sensor for detecting defective UV LEDs. Fig. 4 is a block diagram showing a defective UV LED in the array of Fig. 3 and the reactions of the UV detectors in the UV sensor of Fig. 3 represents. Fig. Figure 5 shows an adjustment of the UV curing operation in response to the detection of defective UV LEDs. Fig. 6 is a flow chart of a process that describes the Fig. 5 shown adjustment operation is implemented. Fig. 7A, Fig. 7B, Fig. 7C and Fig. 7D show alternative embodiments of the printer that allow the UV detector to receive UV light at the UV curing device to detect defective UV sensors. DETAILED DESCRIPTION

[0011] For a general explanation of the present embodiments, reference is made to the drawings. Like reference numerals have been used throughout the drawings to refer to like elements.

[0012] Fig. 1 shows a printing system 100 configured to print on the surface of an object 104 mounted on a fixture 108 as the fixture 108 moves in a process direction indicated by the arrow along an element 116 of an array of printheads 112. If one or more of the printheads 118 in the array 112 eject ultraviolet (UV) ink, the UV curing device 120 is actuated by a controller 124 to cure the UV ink. The controller 124 is also configured to actuate the actuator 128 to move the fixture 108 along the element 116 after the object has been mounted in the fixture. The controller 124 is configured to actuate the print heads 118 in the assembly 112 to eject marking material onto the surface of the object 104.An electrical switch 130 is operatively connected between a power supply 134 and the UV curing device 120. The controller 124 is operatively connected to the switch 130 to selectively couple the power supply 134 to the UV curing device 120. The controller 124 actuates the actuator 138 to move the UV curing device 120 transverse to the process direction, i.e., orthogonal to the process direction of the holder 108, as described in more detail below. A UV detector 142 is positioned opposite the UV curing device 120 to receive UV radiation from the device 120 when neither an object 104 nor the holder 108 is between the detector 142 and the device 120. As used in this document, “UV light” refers to light with a wavelength shorter than that of visible light but longer than that of X-rays.Light in this range has a wavelength of about 10 nm to about 400 nm.

[0013] An embodiment of the holder 108, which is known in the prior art, is shown in Fig. 1B. The holder 108 includes a pair of sockets 132 in which the element 116 is received, and a plate 136. With this configuration, the plate 136 of the holder 108 is offset with respect to the element 116. The printheads 118 are offset cross-process with respect to the longitudinal axis of the element 116 to enable the printheads to eject ink toward the object held in the holder 108. Likewise, the UV curing device 120 and the UV detector 142 are offset cross-process to enable the UV curing device to direct UV light onto the ink image on the object 104 to cure UV-curable ink on the object.Because the UV detector is also offset from the UV curing device in the cross-process direction, it can receive UV light from the UV sensors in the UV curing device when the holder 108 is not located between the UV curing device and the UV detector, as described in more detail below.

[0014] Fig. Figure 2A is a graph showing the output voltage level of a UV sensor in UV detector 142 with respect to the intensity of UV light received at the sensor. As the intensity of UV light increases, the output voltage of the UV sensor increases linearly. This relationship is approximately the same at each of the temperatures shown in the figure. Fig. Figure 2B is a graph showing the spectral sensitivity of the same sensor.

[0015] Fig. Figure 3 is a block diagram illustrating the structure of the UV LED array in the UV curing device 120 and the structure of the UV detector 142 for detecting defective UV LEDs in the UV curing device. The curing device 120 includes a housing 304 and an array of UV LEDs 308A through 308E. The LEDs 308A through 308E are electrically connected to the input voltage terminal 312 and the return terminal 316 so that the UV LEDs of the curing device 120 can be coupled to the power supply 134. The input voltage terminal 312 is connected to the output of the voltage supply device 134 via a switch 130 operated by the controller 124 to selectively couple the voltage supply device 134 to the LEDs in the curing device 120.Although five LEDs 308A to 308E are shown in the figure, the number of LEDs is a number that allows the LEDs to form a continuous line of UV radiation extending transversely to the process direction across the path of the holder 108 for a distance equal to the width of the widest object that can be accommodated by the holder 108.

[0016] As also in Fig. 3, the UV detector 142 includes a housing 320 in which an array of UV sensors 324A through 324E is arranged in a cross-process direction in one-to-one correspondence with the UV LEDs 308A through 308E. Impervious partitions 328 are located between adjacent UV sensors. These partitions shield the individual UV sensors from UV radiation produced by UV LEDs that are not directly opposite a particular UV sensor. This configuration helps ensure that each UV sensor corresponds to the UV LED in the curing apparatus 120 that is directly opposite the UV sensor.The outputs of UV sensors 324A through 324E are provided to controller 124 to enable the controller to detect any defective UV LEDs by reference to the output signals, while UV LEDs 308A through 308E of UV curing device 120 are actuated to direct UV light into UV sensors 324A through 324E of UV detector 142, respectively. Controller 124 compares these signals to a predetermined threshold to determine whether any of the LEDs are detected as defective. In one embodiment, the UV sensors are part number ML8511, manufactured by SparkFun Electronics of Niwot, Colorado, but other suitable UV sensors may be used. A user interface 340 is operatively connected to the controller 124 to enable the controller to generate instructions for maintenance of the UV curing device 120, as described in more detail below.

[0017] Fig. Figure 4 is a block diagram illustrating a defective UV LED in the array of LEDs 308A through 308E and the responses of UV sensors 324A through 324E in the UV detector. As shown in the figure, UV LED 308B of curing device 120 produces no UV light at all, as indicated by the absence of arrows emanating from this LED. As a result, UV sensor 324B, which is opposite UV LED 308B, produces an output voltage level lower than threshold 250, which corresponds to the lowest UV intensity sufficient to cure UV ink on an object. The remaining UV LEDs 308A and 308C through 308E produce an amount of UV radiation sufficient to cause the output voltages produced by the remaining UV sensors to exceed the threshold. Therefore, the controller 124 detects the UV LED 308B in the UV curing device 120 as the only defective LED in the device 120.

[0018] Once a defective UV LED has been detected by the controller 124 based on the signals generated by the UV sensors 324A through 324E in the UV detector 142, adjustments can be made to the placement of the UV curing device 120 to enable the printer 100 to continue its operation without having to replace the defective LED. Fig. Figure 5 illustrates an adjustment of the UV curing operation in response to the detection of defective UV LEDs. The figure shows ten different scenarios of failure of UV LEDs 504, 508, 512, 516, 520, 524, 528, 532, 536, and 540. In scenario 504, the UV LEDs are identified by the reference numerals used above, i.e., 308A to 308E. These reference numerals also apply to the UV LEDs in the other scenarios described in Fig. 5. In scenario 504, the UV LED 308A is detected as defective. To address this situation, the controller 124 actuates the actuator 128 to move the fixture 108 and the object 104 in a first pass along the UV curing device 120 to enable the UV LEDs 308B through 308E to cure UV ink on the object. The controller 124 then actuates the actuator 138 to move the UV curing device 120 to the left across the width of a UV LED radiation pattern, and then actuates the actuator 128 to move the fixture 108 and the object 104 through the line of UV radiation generated by the repositioned curing device 120. This repositioning enables the LED 308B to replace the defective LED 308A and irradiate the UV ink during its second pass along the curing device.Scenarios 508, 512, 516, and 520 are scenarios in which only one UV LED is detected as defective. In each of these scenarios, the controller 124 actuates the actuators 128 and 138 in a manner similar to that described with reference to scenario 504 to pass the fixture 108 and the object 104 twice past the UV curing device 120 and to cure the UV curing device a distance corresponding to the width of a UV LED irradiation pattern over the two passes to allow an uncured area on the object 104 to be cured by a functional UV LED in the device 120. Other possible repositioning movements may achieve the same goal.

[0019] In scenarios 524, 528, 532, 536, and 540, two LEDs in the curing device 120 were detected as defective. Again, in response to the detection of the defective LEDs, the controller 124 actuates the actuators 128 and 138 in a manner similar to that described with reference to scenario 504 to pass the fixture 108 and the object 104 twice past the UV curing device 120 and to cure the UV curing device a distance corresponding to the width of a UV LED irradiation pattern over the two passes to allow both uncured areas on the object 104 to be cured by two functional UV LEDs in the device 120. Other possible repositioning movements may achieve the same goal.

[0020] Although multiple repositionings of the curing fixture 120 in combination with more than two passes can be used to address other defective LED scenarios, they are considered too inefficient to be implemented. For example, if both LED 308A and LED 308E are detected as defective, a workaround would then require three passes and two cross-process direction moves to reposition the curing fixture. In such a scenario, a repositioning would move the fixture 120 either to the right or to the left across a path of an irradiation pattern to cure the area not cured by the rightmost or leftmost defective LED.To remedy the situation where an area remains uncured, the curing device is then moved a distance equivalent to two irradiation pattern widths in the opposite direction along the axis transverse to the process direction. These multiple passes and repositioning actions can consume time, making printing and curing images on objects inefficient. Instead, the controller 124 could generate a signal to a user interface 340 to indicate that the UV curing device 120 requires maintenance to replace the defective LEDs before the printer returns to its operational state.

[0021] A process of operating the printer 100 is shown in Fig. 6. In the description of the process, statements that the process performs a particular task or function refer to a controller or general-purpose processor executing programmed instructions stored in a non-transitory, computer-readable storage medium operatively connected to the controller or processor to control one or more components in the printer to perform the task or function. The controller 124 referred to above may be such a controller or processor. Alternatively, the controller may be implemented with more than one processor and associated circuitry and components, each configured to perform one or more tasks or functions described herein.Furthermore, the steps of the method may be performed in any possible chronological order, regardless of the order shown in the figures or the order in which the processing is described.

[0022] Fig. 6 is a flow chart of a process that describes the Fig. 5 is implemented. The process begins by actuating the UV curing device 120 while the device is aligned with the UV sensors 308 in the UV detector 142 in a one-to-one correspondence (block 604). The controller 124 compares the output signal from each UV sensor to determine if all UV sensors are functioning (block 608). If all are functioning, the object is printed, and a single pass of the UV curing device is sufficient to cure the UV ink printed on the object (block 612). If one or more defective LEDs are detected, the process identifies the defective UV LEDs (block 616) and determines if the defective pattern can be addressed with a two-pass solution (block 620). If so, appropriate repositioning is performed between the two runs to implement two-pass printing of the object (block 624).Otherwise, the controller generates an indication that the UV curing device requires maintenance to replace defective LEDs (block 628). Once an object has been printed by printing objects in either one or two passes, the process determines whether to print another object (block 632). If another object is ready to be printed, the UV LEDs are checked before printing (blocks 604 and 608). Otherwise, the process waits until another object is ready to be printed.

[0023] Other embodiments of the printer 100 are shown in which the components are structured differently to enable the UV LEDs in the curing device to illuminate the UV sensors in the UV detector. Fig. 7A, the mount 108 includes a single bushing 160 that receives the element 116. The bushing 160 has a length greater than a gap distance between one end 116A and one end 116B of the element 116. This configuration allows the printhead assembly 112 to be positioned opposite the element 116, rather than offset relative to the element as described above. The gap distance allows the bushing 160 to continue to the upper portion 116C, allowing the UV curing device 120 to direct UV light onto the object 104. Fig. 7B, element 116 is uninterrupted, but again, the printhead assembly 112 is located opposite element 116 rather than offset from it. The UV detector 142 extends from the socket 160. This configuration allows the UV detector to pass opposite the UV curing device 120 before the object passes the UV curing device. Thus, the UV curing device directs light into the UV detector, causing the UV sensors in the UV detector to generate signals that are processed by the controller 124, allowing the controller to detect any defective LEDs and determine whether a one-pass or two-pass process can be performed to cure the ink image on the object. Fig. 7C, element 116 is uninterrupted, but again, printhead assembly 112 lies opposite element 116 rather than being offset from it. Additionally, UV detector 142 is positioned at an angle relative to element 116. An element 168 having a reflective surface extends from socket 160. This reflective surface is tilted at an angle that allows UV light emitted by the UV curing device to be reflected into the UV detector. Again, this element 168 and its reflective surface allow for detection of defective UV LEDs and for determining the feasibility of a one-pass or two-pass process for printing objects before the object advances to the UV curing device. Fig. 7D, element 116 is uninterrupted, but again, the printhead assembly 112 is opposite element 116 rather than offset from it. In this embodiment, actuator 138 ( Fig. 1) further configured to rotate the UV curing device to face the UV detector 142, which is positioned on the same side of the element 116 as the UV curing device 120. When the controller 124 actuates the actuator 138 to rotate the UV curing device 120, the UV curing device faces the UV detector to enable detection of any defective LEDs and to determine the feasibility of a single-pass or two-pass process. If printing on an object is possible, the controller 124 actuates the actuator 138 to return the UV curing device to its home position to enable curing of the UV ink on the surface of the object.

[0024] It should be understood that variations of the above-disclosed devices and other features or functions, or alternatives thereto, may be combined as desired to form many other different systems or applications. Although the above-disclosed defective UV LED detector has been described as being used in a DTO printer, the detector may also be used in printing systems that eject UV-curable inks onto print media to form images on the media and then cure them. Various alternatives, modifications, variations, or improvements not currently contemplated or anticipated may be made by one skilled in the art in the future, and these alternatives are also intended to be encompassed by the following claims.

Claims

[1] Printing system (100), comprising: a plurality of printheads (118), each printhead (118) of the plurality of printheads being configured to eject a marking material; an element (116) having a first end and a second end, wherein the plurality of printheads (118) are positioned between the first and second ends of the element (116); a holder (108) configured to hold an object (104) and to move along the element (116) between the first and second ends of the element (116); a first actuator (128) operatively connected to the support (108) to enable the actuator (128) to move the support (108) along the member (116) and move the object (104) past the printheads (118) to receive marking material from the printheads (118) of the plurality of printheads; an ultraviolet (UV) curing device (120) having a plurality of UV light emitting diodes (LEDs), each UV LED in the UV curing device (120) being configured to emit UV light, wherein the UV curing device (120) is positioned between the plurality of print heads (118) and the second end of the member (116) to enable the UV curing device (120) to cure UV marking material ejected onto the object (104) after the object (104) has passed the plurality of print heads (118); a second actuator (138) operatively connected to the UV curing device (120); a UV detector (142) having a plurality of UV sensors and uninterrupted partitions (328) between adjacent UV sensors to shield the individual UV sensors from UV radiation produced by UV LEDs that are not directly opposite a particular UV sensor, each UV sensor being configured to receive UV light from one of the UV LEDs in the UV detector (142) and generate an electrical signal corresponding to an intensity of the UV light received at the UV sensor; and a controller (124) operatively connected to the plurality of print heads (118), the first actuator (128), the second actuator (138), the UV curing device (120) and the UV detector (142), the controller (124) being configured to actuate the first actuator (128) to move the holder (108) and the object (104) along the element (116) in a process direction and to enable the plurality of print heads (118) to eject marking material onto the object (104) as the object (104) has passed the print heads (118) in the plurality of print heads, and to control the UV curing device (120) to direct UV light onto the UV detector (142), to receive the electrical signals generated by the UV sensors in the UV detector (142), and to detect any UV LEDs in the UV curing device (120) that do not emit UV light at at least a predetermined intensity, by comparing a voltage of each electrical signal received by the UV sensors in the UV detector (142) with a predetermined voltage level corresponding to the predetermined intensity, detecting the UV LEDs that do not emit UV light with at least the predetermined intensity, and actuate the second actuator (138) to move the UV curing device (120) transversely to the process direction over a predetermined distance to enable a functioning UV LED in the UV curing device (120) to emit UV light onto an area of the object (104) in the holder (108) that has been opposite a UV LED that was identified as not emitting UV light at least at the predetermined intensity. [2] The printing system (100) of claim 1, wherein the holder (108) further comprises: a plate (136); and at least one bushing (132) receiving the element (116) to enable the holder (118) to slide along the element (116), wherein the at least one bushing (132) is connected to a surface of the plate (136) opposite a surface of the plate (136) facing the plurality of print heads (118) and the UV curing device (120) to enable the element (116) and the plate (136) to slide along opposite the plurality of print heads (118) and the UV curing device (120). [3] The printing system (100) of claim 2, wherein the element (116) has an upper portion and a lower portion that are vertically aligned and separated from each other by a predetermined distance, the predetermined distance being less than a length of the at least one bushing (132); and the UV curing device (120) and the UV detector (142) are opposite each other, the distance of the upper portion of the element (116) and the lower portion of the element (116) being arranged between the UV curing device (120) and the UV detector (142). [4] The printing system (100) of claim 1, wherein the UV detector (142) extends from the holder (108) in the process direction.

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