Method for generating variable length strobe pulses with reference to image distance

A method of operating a printer enables activation signals of variable lengths to be generated for operation of a sintering head. The activation signals are generated with reference to a distance between activation signals for a first component to be a first determined distance and a duration of the activation signals for the first component to be longer than the first predetermined distance. This distance and duration are set to values that enable the generation of activation signals before the first predetermined distance is reached to maintain an activation signal until the generation of the activation signals is terminated. By generating a different number of activation signals, the duration of an initial activation signal can be varied.

TECHNICAL FIELD

This disclosure relates generally to printing systems, and more particularly, to controlling substrate processing components in such printing systems.

BACKGROUND

In printing systems, printheads and substrates on which they print move relative to one another. To synchronize the emission of the material from the printheads to particular locations on the substrates, clocks, devices that measure substrate movement distances, and position detectors are used. The signals generated by these components are received by a controller and analyzed to determine the speed of a moving substrate or printhead and to determine a future time at which an ejector in the printhead is opposite a particular position where material should be ejected. A signal that activates the ejector is sent to the ejector immediately before that position is reached so the ejector is activated to eject a drop of material at the predetermined position.

In some known inkjet printers, the signals that activate ejectors in printheads are called DotClock signals. These DotClock signals are typically based on positional input from an encoder that is associated with a roller that moves a substrate through the printer prior to the substrate being printed. These rotary encoders are optical or electromagnetic sensors that convert the angular position of the roller from an index position into an electrical signal. With information regarding the radius or diameter of the roller along with the current angular position, the controller can determine when a portion of the substrate currently at the roller is positioned elsewhere in the printer. This positional data, rather than strictly time-based data, is used so variation in the substrate transport speed can be taken into account, which results in significant accuracy of substrate location positions. In other known systems, a linear encoder is used to convert the linear position of a tag on a component carrying a substrate as the component moves through the system into an electrical signal that is used as positional data for substrate movement.

Printing system technology has been adapted to form electronic circuits on flexible substrates. In these printing systems, a printhead array ejects conductive ink onto the flexible substrates to form ink images of electronic traces on the substrates. The printed flexible substrates bearing the liquid ink images of the electronic traces are then moved past a sintering head that exposes the liquid ink image to an intense light that hardens the liquid ink and bonds the traces to the substrate. The substrates continue to move past the sintering head to another machine that populates the flexible substrates with electronic components and applies solder to install the components in the electronic traces. The completed flexible substrates can then be installed in devices. Operating the lamps in sintering heads differs from known printhead activation technology because the DotClock signals for inkjet printheads react to the rising edge of the signal and the duration of the pulse in the signal is not important. The lamps in the sintering heads, however, require the activation signal to remain at the activating amplitude to keep the lamp shining while the printed circuits are opposite the lamps. The DotClock signal in known inkjet printers provide a rising edge that precisely indicates that a position on a substrate has traveled a specific distance and reached a particular location at a specific point in time. This signal, however, does not have to maintain the amplitude present at the rising edge for the ejector since it only ejects one drop and does not eject another drop until another DotClock signal is received. Rather than redesigning the DotClock signal generator that drives a sintering head so it produces activation signals for the lamps in sintering heads that correspond to different periods of illumination for different lengths of circuits formed on flexible substrates, a less drastic modification of the DotClock signal generator operation would be beneficial.

SUMMARY

A method of operating a printer enables a sintering head activation signal to be varied with different durations without significant alteration of known inkjet ejector activation signal generators. The method includes setting a distance between generation of activation signals for a first component to be a first determined distance, setting a duration of each activation signal for the first component to be longer than a time period corresponding to the first predetermined distance, identifying a number of activation signals that operate the first component for processing a predetermined length of a substrate, generating a first activation signal for the first component in response to the substrate reaching the first component, and continuing to generate additional activation signals for the first component as the first predetermined distance is reached following generation of each activation signal until the identified number of activation signals have been generated.

A system that exposes substrates having variable lengths to radiation emitted by a curing device enables a curing device activation signal to be varied with different durations without significant alteration of known inkjet ejector activation signal generators. The system includes a cart configured to move the substrate along a track past a first component, a first component configured to treat the substrate as the cart passes the first component, and a controller. The controller is configured to set a distance between generation of activation signals for the first component to be a first determined distance, set a duration of each activation signal for the first component to be longer than a time period corresponding to the first predetermined distance, identify a number of activation signals that operate the first component for processing a predetermined length of a substrate, generate a first activation signal for the first component as the substrate approaches the first component, and continue to generate additional activation signals for the first component as the first predetermined distance is reached following generation of each activation signal until the identified number of activation signals have been generated.

A printing system for producing printed circuits on substrates enables a sintering head activation signal to be varied with different durations without significant alteration of known inkjet ejector activation signal generators. The printing system includes a cart configured to move the substrate along a track past a sintering head, a sintering head configured to treat an electrical circuit on the substrate, and a controller. The controller is configured to set a distance between generation of activation signals for the sintering head to be a first determined distance, set a duration of each activation signal for the sintering head to be longer than a time period corresponding to the first predetermined distance, identify a number of activation signals that operate the sintering head for processing a predetermined length of a substrate, generate a first activation signal for the sintering head as the substrate approaches the sintering head, and continue to generate additional activation signals for the sintering head as the first predetermined distance is reached following generation of each activation signal until the identified number of activation signals have been generated.

DETAILED DESCRIPTION

A system for manufacturing printed circuits on flexible substrates is shown inFIG. 1. The system100includes a printhead array104, a sintering head108, an electronic component installer112, and a controller118. Controller118operates an actuator132to propel a cart120along a track136in a process direction to move a flexible substrate124held to its upper surface past the printhead array104, the sintering head108, and the electronic component installer112. Detectable marks are located at precise intervals on the track136and an encoder128is mounted to the cart120to detect the marks and generate a signal indicating detection of a mark. An unique index mark is provided in the detectable mark and it is used as a fixed position reference when detected by the encoder. Prior to sending the cart120and the substrate124through the system100, the controller118sends data to the DotClock generator116and the DotClock generator120identifying the number of marks past the index mark these generators are to begin generating activation signals for the operation of the printhead array104and the sintering head108, respectively. As used in this document, the term “process direction” refers to the direction of movement of flexible substrates past the printhead array104, the sintering head108, and the electronic component installer112to the discharge area from the system100, while the term “cross-process direction” refers to a bidirectional path of movement that is perpendicular to the process direction in the plane of the flexible substrates. The movement of the cart120along track136is in the process direction and the movement of the printhead array104across a width of the substrate124is in the cross-process direction.

The printhead array104is comprised of one or more known inkjet printheads that are operated in a known manner to eject drops of conductive ink onto flexible substrates as the substrates are moved opposite the printheads. The conductive inks ejected by the printhead array104contain electrically conductive particles suspended in a fluid medium. As the cart120carries the flexible substrate124past the printhead array104, the DotClock generator116generates activation signals for the firing of the inkjets in the printheads based on signals from the encoder128and a reference clock. As discussed previously, these activation signals have a predetermined duration that cannot be varied in length to correspond to different illumination periods and these signals are time-based. The printhead array104can also be moved in the cross-process direction to enable finer resolution of the ejected drops per unit of distance. For example, printheads in the array104can be configured to eject drops at a resolution of 300 drops per inch (dpi). By moving the printheads in the cross-process direction a distance approximately one half of the distance between adjacent ink drops in a line extending in the cross-process direction, the resolution of the line of drops can be increased to 600 dpi. Even finer movement of the printheads in the cross-process direction can increase the resolution to 1200 dpi or up to 2400 dpi.

After the electrical circuits are formed with the conductive inks on the flexible substrate, the controller118operates the actuator132to move the cart120and the substrate124through the sintering head108and on to the component installer112. The sintering head108is a device having a plurality of lamps mounted within a hood. These lamps extend in a linear array in the cross-process direction. An example of a sintering head is a PulseForge tool available from Novacentrix of Austin, Tex. These lamps continuously generate a light strobe as long as they receive an activation signal of a predetermined amplitude. The light emitted by the lamps in the sintering head108transforms the liquid conductive ink to a solid and bonds the metal particles in the conductive ink to the flexible substrate. This operation forms electrical circuit traces on the flexible substrates in the pattern of conductive ink printed by the printhead array104. Activation signals for the lamps in the sintering head108are generated by the DotClock generator120and this DotClock generator120receives positional data signals from the encoder128to determine the position of the flexible substrate as it approaches the sintering head108. The DotClock generator120is different than the DotClock generator116because the generator120can produce activation signals having variable durations as described more fully below.

The cart120and the flexible substrate124bearing the hardened electrical circuits leave the sintering head108and continue along the track136to the component installer112. Component installer112is a known device that uses an articulated arm or the like to install electronic components at appropriate locations on a printed circuit and solder the components to those locations. When all of the components have been installed and soldered on the circuit, the cart120carries the flexible substrate to a location for off-loading and then the cart120returns to the starting position on the track136for another substrate.

Operation of the printhead array104depends upon the DotClock generator116, which is configured to determine when an inkjet activation signal should be generated and delivered to an inkjet in a printhead in array104for firing the inkjet. This determination is made with reference to a predetermined distance between activation signals, which are also called DotClock signals, and the number of DotClock signals to generate. When the first DotClock signal is generated and delivered to an inkjet, a counter adds the predetermined distance to the current encoder value to obtain the encoder value for the generation of the next activation signal. This process continues until the electrical circuit has been printed and data processing for the next flexible substrate begins. When each activation signal is generated and delivered, the rising edge of each signal becomes high for a fixed amount of time but that signal duration does not further activate the ejector receiving it. This high signal duration is normally acceptable for ejectors that eject a predetermined amount of liquid ink. When the duration of the activation signal becomes important, as it does for operation of a sintering head to provide different periods of illumination, the arbitrary activation pulse duration results in improper circuit trace formation since the signal amplitude drops to zero before the next activation signal generation position is reached. Adding another register in a DotClock generator to specify a variable duration of a single activation signal that maintains the high state of the signal for the length of the circuit could solve this problem but this solution requires additional memory as well as changes to both the DotClock generator software and to the field programmable gate array (FPGA) operating the DotClock generator. Also, this type of signal generation is time-based rather than position-based and is susceptible to slips and other changes in the constant velocity of substrate movement caused by the positional components moving the substrates through the sintering head. These velocity changes adversely affect the operation of a sintering head. In general, a time-based tracking system is only accurate if velocity remains constant. Variations in velocity, which are unavoidable in known systems, produce error in tracking a substrate when the tracking is done in the time-domain.

To address the need to have an activation signal with a variable duration for operating a sintering head or the like, a method operates the DotClock generator120to produce activation signals with different durations. As noted previously, the DotClock generator120receives data identifying a number of marks past the index mark where the cart and substrate reach the sintering head108and it also receives data identifying the number of activation signals required to keep the sintering head108operating as the printed circuit passes the sintering head.

As the cart120moves along the track136, the DotClock generator120receives the signal from the encoder128and identifies when the flexible substrate124reaches the sintering head108. The encoder128could be a rotary encoder associated with a wheel or other rotating component of the cart but since the movement of the cart is along a linear track, a linear encoder is used in the system ofFIG. 1to detect the marks along the track path. Once the circuit on the substrate124is in position for exposure, the DotClock generator120generates the first activation signal of the identified number of activation signals. To maintain this activation or DotClock signal long enough to expose the entire length of the circuit without requiring the changes noted above to existing DotClock generators, two parameters used for operation of the FPGA are adjusted to adapt the printhead controller to this purpose. One of these parameters is signal duration. By setting the signal duration to be longer than the distance between generation of the activation signals, another activation signal is generated before the previous activation signal has terminated. Generating each activation signal of the identified number of activation signals as the distance between each signal generation is reached enables the active state of the first activation signal to be maintained until the last activation signal expires. Thus, a single long activation signal is produced by the DotClock generator120and its length depends upon the number of activation signals generated. Because the activation signal duration is maintained by the continued generation of activation signals, which are generated with reference to the distance to the next signal and the position signal received from the encoder128, this single activation pulse is based on solely on positional data from the encoder. Thus, this extended signal very accurately locates the beginning and the end of the exposure length for a circuit on a substrate. Resolution for the length of this pulse is limited only by the setting of the distance between activation signals. This method does not require a unique signal duration parameter, which is assigned different values by software for different substrates. Instead, the method only requires that the signal duration be set to a fixed value larger than the distance between the generation of DotClock signals in constant-strobe mode or to a short duration in normal mode used for activating inkjets in printheads.

A process for operating the DotClock generator120in the system100is shown inFIG. 2. In the description of the process, statements that the process is performing some task or function refers to a controller or general purpose processor executing programmed instructions stored in non-transitory computer readable storage media operatively connected to the controller or processor to manipulate data or to operate one or more components in the printer to perform the task or function. A controller for the system100noted above can be a FPGA. Alternatively, the controller can be implemented with one or more processors operating associated circuitry and components, each of which is configured to form one or more tasks or functions described herein. Additionally, the steps of the process may be performed in any feasible chronological order, regardless of the order shown in the figures or the order in which the processing is described.

The method shown inFIG. 2begins with setting the duration of the DotClock signal for the activation signals generated by the DotClock generator120for the sintering head to be longer than the distance between the generation of activation signals (block204). This setting can be done in response to a check of the data stored in an internal register or with reference to a signal generated by a hardware switch. Prior to the controller118operating the actuator132to move the cart120through the system100, the process determines the position past the index mark at which activation signal generation begins and the number of activation signals needed to expose the circuit on the substrate (block208). As the DotClock generator monitors the signal from the encoder128, the process determines whether a printed substrate is entering the sintering head (block212). If it is not, it waits until a printed substrate is ready to enter the sintering head. Once the positional data from the encoder indicates a printed substrate is ready to enter the sintering head, the first activation signal is generated (block216). The DotClock output to the sintering head goes high and the process begins checking whether the distance between activation signals has been reached (block220). Once the activation signal distance is reached, the process determines whether the last activation signal has been generated (block224). If it has not been generated, then another activation signal is generated (block216) to keep the DotClock output high while the substrate is opposite the sintering head. Once the last activation signal is generated (block224), no further activation signals are generated after the expiration of that last signal and the DotClock output falls to zero. The process then determines whether another substrate is to be processed (block232) and, if it is, the process identifies the first DotClock signal generation position for the next circuit and the number of DotClock signals needed to expose the entire length of the circuit on the printed substrate (block208). Otherwise, no further printed substrates remain for processing and the process is terminated.

The previously known DotClock signal generator116operates as shown inFIG. 4. With reference to a 100 MHz clock, activation signals are generated approximately 65 ns apart, but the DotClock duration is set to 25 ns. Therefore, the DotClock output drops to zero from a logic one state before the next activation signal is generated. InFIG. 3, the activation signals are still generated at approximately 65 ns intervals, which corresponds to the distance between marks on the track at a predetermined speed, but the duration of the DotClock output is approximately 75 ns. Therefore, if an additional activation signal is generated because a number of marks corresponding to the distance between signal generations has been detected, the DotClock output remains high for at least another 75 ns and possibly longer if another activation signal is generated as described above.

In operation, a known DotClock generator is operatively connected to a sintering head. The parameter for duration of the signal produced by this generator is set to be longer than the distance between the generation of the activation signals. Thereafter, the controller provides the starting position for the generation of the activation signals and the number of DotClock signals needed to expose the full length of the circuit. The DotClock generator then uses the encoder data to determine when the circuit has reached the sintering head and generates the identified number of activation signals separated by the predetermined generation distance so the sintering head generates light strobes to solidify the conductive ink pattern. Thus, the DotClock output remains high until the entire length of the circuit has been exposed and the flexible substrate exits the sintering head. The DotClock generator stops generating activation signals until another printed substrate is ready to enter the sintering head. In this manner, the DotClock generator120precisely commences sintering head operation when the substrate has entered the sintering head and precisely deactivates the sintering head when the entire length of the circuit has been exposed. This embodiment of a DotClock generator produces activation signals of different durations for variable operation of the sintering head to expose printed electrical circuit patterns of different lengths.