Patent Publication Number: US-11660891-B2

Title: Inkjet printer with temperature controlled substrate support

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 16/713,218, filed Dec. 13, 2019 and claims benefit of U.S. Provisional Patent Application Ser. No. 62/782,595 filed Dec. 20, 2018, and U.S. Provisional Patent Application Ser. No. 62/814,529 filed Mar. 6, 2019, each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     Embodiments of the present invention generally relate to inkjet printers. Specifically, methods and apparatus for substrate temperature control during processing are described. 
     BACKGROUND 
     Inkjet printing is common, both in office and home printers and in industrial scale printers used for fabricating displays, printing large scale written materials, adding material to manufactured articles such as PCB&#39;s, and constructing biological articles such as tissues. In some cases the precision required in depositing materials on a substrate by inkjet printing is extreme. For example, in display applications, materials may be printed onto a substrate using droplets of liquid print material having dimensions of 10-15 μm that are deposited at targets locations of dimension about 20 μm. For large substrates, a change in temperature of the substrate can result in dimension changes in the substrate exceeding the size of the target location, leading to droplet location uncertainty that results in printing faults. 
     There is a need for strict temperature control of large substrates during inkjet printing processes. 
     SUMMARY 
     Embodiments described herein provide an inkjet printer, comprising a gas cushion substrate support having a metal support surface; a print assembly with a dispenser having ejection nozzles facing the support surface; a gas source fluidly coupled to the gas cushion substrate support by a gas conduit; and a thermal control system coupled to the gas conduit. 
     Other embodiments described herein provide an inkjet printer, comprising a gas cushion substrate support comprising a first staging area, a second staging area, and a printing area; a print assembly with a dispenser having ejection nozzles facing a support surface of the printing area; a gas source fluidly coupled to the first staging area by a first gas conduit, to the second staging area by a second gas conduit, and to the printing area by a third gas conduit; and a thermal control unit comprising a heat exchanger thermally coupled to at least the first gas conduit. 
     Other embodiments described herein provide an inkjet printer, comprising a gas cushion substrate support comprising a first staging area, a second staging area, and a printing area; a print assembly with a dispenser having ejection nozzles facing a support surface of the printing area; a gas source fluidly coupled to the first staging area by a first gas conduit, to the second staging area by a second gas conduit, and to the printing area by a third gas conduit; a thermal control unit comprising a plate heat exchanger connected to at least the first gas conduit, a thermal element, and a thermal medium conduit connecting the heat exchanger to the thermal element; a gas effluent conduit connecting the plate heat exchanger to the first staging area; and a temperature sensor thermally coupled to an interior of the gas effluent conduit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments. 
         FIG.  1    is an isometric view of an inkjet printer according to one embodiment. 
         FIG.  2 A  is a detailed view of a thermal control system for use with the inkjet printer of  FIG.  1   , according to one embodiment. 
         FIG.  2 B  is a detailed view of a thermal control system for use with the inkjet printer of  FIG.  1   , according to another embodiment. 
         FIG.  2 C  is a detailed view of a thermal control system for use with the inkjet printer of  FIG.  1   , according to another embodiment. 
         FIG.  2 D  is a detailed view of a thermal control system for use with the inkjet printer of  FIG.  1   , according to another embodiment. 
         FIG.  3    is an isometric view of an inkjet printer according to another embodiment. 
         FIG.  4    is a schematic plan view of a printing system according to one embodiment. 
         FIG.  5    is a flow diagram summarizing a method according to another embodiment. 
         FIG.  6    is an isometric view of an inkjet printer according to another embodiment. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     An inkjet printer is described herein with support alignment features.  FIG.  1    is an isometric view of a portion of an inkjet printer  100  according to one embodiment. The printer  100  features a base  108 , which is a structurally strong and stable material such as granite, a print assembly  104  disposed on the base  108 , and a substrate support assembly  101  disposed on the base  108 . The substrate support assembly  101  includes a substrate support  102  having a substrate support surface  110  over which a substrate is disposed for processing. The substrate is supported above the substrate support surface  110  by a gas cushion. 
     The print assembly  104  includes a dispenser support assembly  116  comprising a rail  117  coupled to a pair of stands  120 . The stands  120  are disposed on the base  108  on either side of the substrate support  102 . The rail  117  is oriented transverse to the substrate transportation direction, in a “cross-scan” direction, and extends across the substrate support surface  110  in the cross-scan direction. A dispenser assembly  114  is movably coupled to the rail  117 , and moves along the rail  117  to position the dispenser support assembly  114  at target locations with respect to a substrate disposed supported by the substrate support  102 . The dispenser assembly  114  includes a dispenser housing  119 , which holds one or more dispensers (not shown), coupled to a carriage  122 . The carriage  122  is coupled to the rail  117 , for example by a bearing apparatus or assembly, such as an air bearing, and is moved along the rail by a linear actuator. The dispenser assembly  114  can move substantially from one stand  120  to the opposite stand  120  in the cross-scan direction to access substantially all of the transverse dimension of the substrate supported by the substrate support  102 . The stands  120  and the rail are made of structurally strong, stable material and may be integral with the base  108 . 
     The substrate support  102  is a gas cushion support. The substrate support  102  creates a gas cushion along the support surface  110  of the substrate support  102 . A substrate is supported on the gas cushion above the surface  110 . The substrate is thus able to move essentially frictionlessly along the surface  110 . A holder assembly  106  is disposed near an edge  130  of the substrate support  102  to contact an edge region of a substrate disposed on the substrate support  102 . A contact member  142  of the holder assembly  106  contacts the edge region of the substrate and applies vacuum to acquire a secure hold on the substrate. The holder assembly  106  moves the substrate on the gas cushion to position the substrate for deposition of material on the substrate from the dispenser  119 . The holder assembly has a holder carriage  131  that is coupled to a holder rail  128 . The holder rail  128  extends along the edge  130  of the substrate support  102  substantially the entire length thereof to provide the holder assembly  106  freedom to move the substrate from one end of the substrate support  102  to the opposite end. The holder rail  128  may be formed integrally with the base  108  or attached to the base  108 . 
     The support surface  110  has a plurality of holes  112  that flow gas through the support surface  110  to form the gas cushion that supports the substrate. The holes may be specially formed in the support surface  110 , or the support surface  110  may be made of a porous material, thus giving rise to holes naturally. Gas is supplied below the support surface  110  into one or more plenums (not shown) that distribute gas to the holes  112  to provide uniform gas flow and gas cushion support for the substrate. The substrate support assembly  101  includes a blower  132  that provides gas, for example air, conditioned air, oxygen depleted air, nitrogen, or other inert gas, to the substrate support  102  to form the gas cushion at the surface  110 . The blower  132  is fluidly coupled to the surface  110  by a gas conduit  134 . 
     In operation, a substrate is disposed on or above the substrate support surface  110  near an end of the substrate support  102 . The gas cushion is established before or after the substrate is disposed on or above the substrate support surface  110 . An edge region of the substrate engages with the holder assembly  106 , which acquires a secure connection with the substrate by the contact member  142 . The holder assembly  106  then translates along the holder rail  128  to move the substrate in a first direction  124  along the support surface  110  to bring the substrate into processing position between the stands  120  such that print nozzles of the dispensers in the dispenser housing  119  are facing the substrate. The dispenser assembly  114  moves along the rail  117  in a second direction  126  transverse to the first direction  124 , while the holder assembly  106  moves the substrate in the first direction  124  to perform a print job. The first direction  124  is sometimes called the scan direction while the second direction  126  is sometimes called the cross-scan direction. 
     In some cases, a substrate to be processed on the printer  100  is large, for example having GEN 8.5 dimensions of 2.2 m×2.5 m. Variation in temperature of such large substrates can result in dimensional changes of 25-50 μm. For printers adapted to deposit drops of material 10-15 μm in dimension into target locations of around 20 μm, such thermal dimension changes inject unacceptable imprecision into the print process. To manage thermal dimensional change of the substrate, the substrate support assembly  101  includes a thermal control system  136  coupled to the gas conduit  134 . The thermal control system  136  includes a thermal unit  138  coupled to a heat exchanger  140 . The blower  132  is also coupled to the heat exchanger  140 , which is also coupled to the gas conduit  134 . 
     The printer  100  is controlled by a controller  129 , which is coupled to the print assembly  104 , the holder assembly  106 , and the thermal control system  136 . An optional print assembly controller  118  is coupled to the print assembly  104 , and here the controller  129  is coupled to the print assembly controller  118 . The holder assembly  106  may also have a controller coupled to the controller  129 . The controller  129  controls positioning of the dispenser assembly  114 , positioning of the holder assembly  106 , and ejection of print material from the dispensers in the dispenser housing  119  to perform the print job. 
       FIG.  2 A  is a detail view of the thermal control system  136  of  FIG.  1   , according to one embodiment. The heat exchanger  140  shown here is a plate type heat exchanger, but other types of heat exchangers can also be used, such as box heat exchangers, jacketed pipe heat exchangers, and sphere heat exchangers. Gas from the blower  132  is circulated through a conduit  214  of the heat exchanger  140 . The conduit  214  is coupled to the gas conduit  134 , which is, in turn, coupled to a substrate support  202 . The substrate support  202  can be used as the substrate support  102  in the inkjet printer  100  of  FIG.  1   . The thermal unit  138  is coupled to the heat exchanger  140  by a thermal medium conduit  210  through which a thermal medium flow from the thermal unit  138  to the heat exchanger  140 , and by a return conduit  212  through which the thermal medium flows from the heat exchanger  140  to the thermal unit  138 . The thermal unit  138  is a heater or a cooler, or both, depending on the thermal characteristics of the inkjet printer, and the thermal medium may be any fluid suitable for temperatures normally experienced. Water can be used as the cooling fluid in many cases. 
     A temperature sensor  208  is coupled to the gas conduit  134 . The temperature sensor  208  senses a temperature that indicates temperature of the gas flowing in the gas conduit  134 . In one example, the temperature sensor  208  is a thermocouple that is positioned at least partially inside the gas conduit  134  in the flowing gas to directly sense the temperature of the flowing gas. In other examples, the temperature sensor  208  is a non-contact sensor that engages with the gas conduit  134  to sense temperature of the gas, either through direct contact with the gas conduit  134  or through non-contact means, such as optical sensing. The temperature sensor  208  is operatively coupled to the controller  129  to send signals representing the temperature of the gas flowing through the gas conduit  134  to the controller  129 . The controller  129  determines a temperature of the gas from the signals. The thermal unit  138  is also operatively coupled to the controller  129  to receive signals from the controller  129  for controlling operation of the thermal unit  138 . 
     An optional control valve  216  may be disposed in the thermal medium conduit  210  to control a flow rate of the thermal medium to the heat exchanger  140 . Controlling flow of the thermal medium to the heat exchanger  140  can control thermal duty of the heat exchanger  140 , and therefore temperature of the gas flowing to the substrate support  202  through the gas conduit  134 . The controller  129  may also be operatively coupled to the control valve  216 . Thus, the controller  129  receives signals representing temperature of the gas from the temperature sensor  208 , determines temperature of the gas from the signals, compares the temperature to standard, such as a target temperature, and generates control signals to send to the thermal control system  136 . The controller  129  may send control signals to the thermal unit  136 , for example thermal flux signals to control the thermal flux of the thermal unit  136 , the controller  129  may send control signals to the optional control valve  216  to control thermal flux to the heat exchanger  140 , or both. The controller  129  thus controls thermal duty of the heat exchanger  140  based on the temperature readings of the temperature sensor  208 . 
     Thermal state of the gas flowing through the gas conduit  134  is controlled to have a desired thermal effect on the substrate disposed on the substrate support  202 . The gas flows through the openings  112  in the support surface  110  and creates a gas cushion that supports the substrate above the support surface  110 . The temperature of the gas also affects the temperature of the substrate. The thermal flux between the substrate and the gas can be used to reduce variation of substrate temperature, and the accompanying dimensional variation in the substrate that can cause printing faults in precision print jobs. 
     The substrate support  202  is made of a thermally conductive material, such as metal, for example aluminum. The substrate support surface  110  thus also has a thermal effect on the substrate. The substrate support  202  may have a plenum  218  into which the gas flows prior to flowing through the openings  112 . The plenum  218  can serve to distribute the gas evenly among all the holes  112 . The gas enters the body of the substrate support  202  through an inlet  220  and flows into the plenum  218 . From the plenum  218 , the gas flow through the openings  112  in the surface  110 . The gas interacts thermally with the surface  110  and thermally stabilizes the surface  110  relative to environmental thermal effects. In addition to the thermal interaction of the substrate with the gas cushion, the thermally stabilized surface  110  interacts thermally with the substrate positioned just above the surface  110  on the gas cushion to thermally stabilize the substrate. 
     In this way, the temperature of the gas flowing through the gas conduit  134 , detected by the temperature sensor  208 , can be used to thermally stabilize the substrate. If the printing chamber in which printing processes are performed on the substrate warms up due to operation of machinery, a cooler can be used as the thermal unit  138 , and the gas used for the gas cushion can be cooled by the heat exchanger  140 . The cool gas impinges on the substrate and cools the substrate supporting surface  110 . Both the cooled gas cushion and the cool support surface  110  help thermally stabilize the substrate against environmental warming that would change the linear dimensions of a large substrate by up to 50 μm and would cause printing faults. 
       FIG.  2 B  is a detailed view of another thermal control system  150  that can be used as the thermal control system  136  of  FIG.  1   . The thermal control system  150  is similar to the thermal control system  136  of  FIG.  2 A . The thermal control system  150  features a second thermal sensor  222  disposed in the support surface  110  to sense a temperature of the substrate supported above the surface  110  on the gas cushion, or a temperature of the support surface  110  itself. The second thermal sensor  222  may be an optical sensor for sensing the substrate or a contact sensor, such as a pyroelectric or piezoelectric device. Although one thermal sensor  222  is shown disposed in the support surface  110 , multiple such sensors may be used, if desired, to monitor temperature uniformity across the support surface  110 . The thermal sensors  222  may each, individually, be a thermocouple, a thermistor, a bi-metallic thermostat, a resistance temperature detector, or other suitable pyroelectric device or other type of thermal sensor. 
       FIG.  2 B  shows a substrate support  230  with a different internal structure from the substrate support  202 . The substrate support  230  can also be used as the substrate support  102  of  FIG.  1   . Here, the substrate support  230  has at least two internal plenums. A first plenum  232  and a second plenum  234  are shown. Using multiple internal plenums provides additional gas distribution uniformity by forcing the gas to divide into multiple chambers within the substrate support  230 . Such arrangements can be useful to avoid center-to-edge nonuniformity in gas distribution that can lead to higher gas cushion pressure near the center of the support surface  110  than at the edge. 
     The substrate support  230  has an internal distribution manifold  236  that couples the inlet  220  to the first and second plenums  232  and  234 . A first portal  238  fluidly couples the manifold  236  to the first plenum  232 , and a second portal  240  fluidly couples the manifold  236  to the second plenum  234 . The first plenum  232  is separated from the second plenum  234  by a wall  242 . Here, the second temperature sensor  222  is disposed through the wall  242  to access the support surface  110 . In other versions, the second temperature sensor  222  could be disposed through one of the plenums to reach the support surface  110 . As noted above, multiple surface sensors  222  can be used. 
       FIG.  2 C  is a detailed view of a thermal control system for use with the inkjet printer  100  of  FIG.  1   , according to another embodiment. In this embodiment, a substrate support  232  is used that has a support plate  234  supporting a top member  236  that provides the support surface  110 . The holes  112  extend through the thickness of the top member  236 . A gap  238  between the support plate  234  and the top member  236  provides a plenum for gas flow to allow uniform flow of gas through all the holes  112 . The gas flow is provided through a gas flow passage  240  formed through the support plate  234  from a back side  246  of the support plate  234  to the gap  238 . A plurality of gas escape passages  243  are also formed through the support plate  234  and through the top member  236 , from the back side  246  to the surface  110 , to allow gas to evacuate from behind the substrate disposed over the support surface  110 . Temperature controlled gas flows through the gas flow passage  240  to the gap  238  and spreads across the substrate support  232  in the gap  238 . The gas flows from the gap  238  through the holes  112  in the top member  236  to the surface  110  to form a gas cushion of temperature controlled gas that supports a substrate thereon. Gas also flows from the gas cushion between the substrate and the surface  110  through the gas escape passages  243  from the surface  110  to the back side  246  to evacuate from the substrate support  232 . Gas may also flow from the gas cushion to the edge of the substrate, between the substrate and the surface  110  in any of the embodiments of  FIGS.  2 A,  2 B,  2 C, and  2 D  below. 
       FIG.  2 D  is a detailed view of a thermal control system for use with the inkjet printer  100  of  FIG.  1   , according to another embodiment. This version has a different top member  244  that is a porous body. The porous top member  244  has passages through the member that allow gas flow through the porous top member  244 . The top member  244  may be porous metal or ceramic. As a metal, the top member  244  may be a mesh material. As a ceramic, the top member  244  may be a sintered ceramic powder. Using a porous metal material as the top member  244  provides increased thermal control capacity due to thermal conductivity of the metal. 
       FIG.  3    is an isometric view of an inkjet printer  300  according to another embodiment. The inkjet printer  300  is similar to the inkjet print  100  in most respects. The chief difference here is that the inkjet printer  300  has a substrate support assembly  301  with a substrate support  302  that comprises three substrate support sections. A first substrate support section  304  is positioned at a first end of the substrate support assembly  301 . A second substrate support section  306  is positioned in a middle region of the substrate support assembly  301 . A third substrate support second  308  is positioned at a second end of the substrate support assembly  301  opposite the first end. The first substrate support section  304  has a support surface  110  with a first plurality of holes  312  for forming a gas cushion support. The second substrate section  306  has a second plurality of holes  314  for forming a gas cushion support. The third substrate support section  308  has a third plurality of holes  316  for forming a gas cushion support. A first blower  322  is fluidly coupled to the first plurality of holes  312 , a second blower  332  is fluidly coupled to the second plurality of holes  314 , and a third blower  352  is fluid coupled to the third plurality of holes  316 . The second plurality of holes  314  may have a first portion of holes for providing gas to the gas cushion and a second portion of holes for providing suction. Use of gas and suction in the second substrate support section  306  can improve position control of substrates during processing. The second blower  332  is fluidly coupled to the first portion of the second plurality of holes  314 , while a vacuum source (not shown) is coupled to the second portion of the second plurality of holes  314 . 
     Each substrate support section  304 ,  306 , and  308  has a thermal control system. A first thermal control system  326  is coupled to the first substrate support section  304 . A second thermal control system  336  is coupled to the second substrate support section  306 . A third thermal control system  356  is coupled to the third substrate support section  306 . Each of the thermal control systems  326 ,  336 , and  356  features a heat exchanger coupled to a thermal unit to provide thermal control of the gas flowing from the blower to the substrate support. Thus, a first thermal unit  328  is coupled to a first heat exchanger  330  by a first thermal medium conduit that flow thermal medium from the first thermal unit  328  to the first heat exchanger  330 , and by a first return conduit that flow thermal medium from the first heat exchanger  330  to the first thermal unit  328 . Gas flows from the first blower  322  to the first heat exchanger  330 , undergoes thermal contact with the thermal medium in the first heat exchanger  330 , and flow through a first gas conduit  324  to the first substrate support section  304 . The second thermal control system  336  includes a second heat exchanger  340  and second thermal unit  338  coupled with the second blower  332  to provide thermally controlled gas through a second gas conduit  334  to the second substrate support section  306 . The third thermal control system  356  includes a third heat exchanger  360  and third thermal unit  358  coupled with the third blower  352  to provide thermally controlled gas through a third gas conduit  354 . 
     The three separate substrate support sections  304 ,  306 ,  308 , with separate thermal control systems  326 ,  336 , and  356  provide individualized thermal and gas cushion control for the three parts of the substrate support assembly  301 . In this way, the first substrate support  304  can be a staging area for substrates, with the function of establishing gas cushion support and thermal stability of a substrate prior to moving the substrate into a processing position over the second substrate support section  306 . The second substrate support section  306  can provide precise substrate position control using the gas/vacuum controlled gas cushion support of the second substrate support section  306 , along with separate thermal control that can be more precise than that of the first substrate support section  304 , if desired. The third substrate support section  308  can also be a staging area for substrate, with the function of establishing, or maintaining, gas cushion support and thermal stability. In one case, the first and third substrate support sections  304  and  308  can utilize thermal control systems like those described in connection with  FIG.  2 A , while the second substrate support section  306  can utilize a thermal control system like that described in connection with  FIG.  2 B  to provide more precise thermal control for substrates being processed on the second substrate support section  306 . 
     It should be noted that the three substrate support sections  304 ,  306 , and  308  may be separable pieces of hardware, or merely sections of an inseparable piece of hardware. For example, the first, second, and third substrate support sections  304 ,  306 , and  308  may be part of one frame but separated by partitions that segregate gas flow and thermal control among the three sections. Alternately, the first substrate support section  304  may be a separate structure that is removable from the inkjet printer  300 , and likewise for the second and third substrate support sections  306  and  308 . It should also be noted that, in one variation of the system of  FIG.  3   , the first and third substrate support sections  306  and  308  may together use one thermal control system, such as the first thermal control system  326 , omitting the third thermal control system  356 . The gas from the first blower  322  is fluidly coupled to the first and third substrate support sections  304  and  308  and the first blower  322  and first thermal control system  326  are sized accordingly. 
       FIG.  4    is a schematic plan view of a printing system  400 , according to one embodiment. The printing system  400  includes a printing installation  402  that has, in this case, two inkjet printers  404 , each of which may be like the inkjet printers  100  or  300 , and can be different types of inkjet printers. Each inkjet printer  404  in the printing installation  402  has its own blower  406  to form a gas cushion. Here, one blower  406  is shown for each printer  404 , but each printer may have more than one blower  406 , for example if the printer  404  is like the printer  300 . Each printer  404  may also have a vacuum source, like the printer  300 . 
     The printing system  400  has a thermal control system  410  that includes a thermal unit  412  and a heat exchanger  414 . Each blower  406  is fluidly coupled to the heat exchanger  414  to flow gas through the heat exchanger  414  to the corresponding printer  404 . The thermal unit  412  is coupled to the heat exchanger  414  by thermal medium and return conduits. The single heat exchanger  414  and thermal unit  412  provide thermal control to all the printers  404  in the print installation  402 . 
     In alternate embodiments, a single thermal unit can be coupled to multiple heat exchangers, one heat exchanger for each printer, and flow of thermal medium to each heat exchanger can be controlled based on thermal conditions of individual printers. For example, if one printer is generally warmer than another printer, more thermal medium can be flowed to the warmer printer to maintain thermal control of substrates in that printer. In other alternate embodiments, a printing system may include multiple printing installations, each having multiple printers. A single heat exchanger may be used for one printing installation. One thermal unit may provide thermal medium to all the heat exchangers under flow control based on the thermal condition of the individual printing installation. Ratios of heat exchangers to printers to thermal units can be determined by the thermal duty of the printing system. 
       FIG.  5    is a flow diagram summarizing a method  500  according to one embodiment. The method  500  is a method of depositing material on a substrate using a precision printing process. At  502 , a substrate is disposed on a substrate support of an inkjet printer. The printer may be any of the printers described herein, and may be part of a printing installation of a printing system. The substrate is typically a material with at least some structural strength, such as glass, plastic, ceramic, or other similar materials. In many cases, the substrate is large enough that thermal expansion of the substrate over 10° C. temperature change can change the position of a target printing location by 50 μm or more. In some precision printing processes, drops of print material having diameter of 20 μm are deposited at a target location on the substrate having dimension of 30 μm, in some cases smaller, so position changes of 50 μm, or less, can cause printing faults. 
     To manage thermal expansion, the substrate is thermally stabilized using a gas cushion support. At  504 , gas is flows to the substrate support to form a gas cushion between the substrate and the substrate support. The gas cushion is typically 10-50 μm thick, depending on gas flow rate. Oxygen-free or reduced-oxygen gases, such as oxygen depleted air, nitrogen or argon, are frequently used. 
     At  506 , the gas used to establish and maintain the gas cushion is thermally contacted with a thermal control medium. A heat exchanger is typically used. The gas may be flowed through a plenum where tubes carry the thermal control medium through the plenum. The gas contacts the tubes and exchanges heat with the thermal control medium. Alternately, a jacket volume may be provided around the tube carrying the gas, and the thermal control medium may be flowed through the jacket volume. The thermal control medium may be water or any fluid capable of achieving a target temperature for the thermal control medium. In one instance, the thermal control medium is cooled to a temperature of about 5° C. to reduce heating of the substrate. 
     At  508 , a temperature of the gas after the gas thermally contacts the thermal control medium is sensed to determine whether the gas is at or near a target temperature. A thermal sensor is used to sense temperature of the gas. The thermal sensor may be a pyroelectric sensor, such as a thermocouple, in physical contact with the gas. In other cases, a non-contact sensor may be used to sense a temperature of the surface of the tube or pipe carrying the gas away from the location of thermal contact with the thermal control medium. 
     At  510 , flowrate or temperature of the thermal control medium is adjusted based on the gas temperature. If the gas temperature is too high, temperature of the thermal medium may be reduced, or flowrate may be raised or lowered to reduce the gas temperature, and vice versa. A thermal unit, such as a heater or cooler, is typically used to set the temperature of the thermal control medium. If the thermal control medium is close to a phase change temperature of the medium, flowrate of the thermal control medium can be used preferentially to adjust gas temperature. In one case, temperature of the thermal control medium is changed in increments of 0.1° C. every time the temperature is measured outside a tolerance range. For example, a temperature reading may be taken every second, or every half-second, according to parameters of the temperature sensor. Every time the temperature sensor senses a temperature that is above a tolerance range set in the controller, the controller controls the thermal unit to reduce temperature of the thermal control medium by 0.1° C. Every time the temperature sensor senses a temperature that is below the tolerance range, the controller controls the thermal unit to increase temperature of the thermal control medium by 0.1° C. When the temperature sensor senses a temperature that is within the tolerance range, the controller sends no control signal. In other cases, some form of PID control, or heuristic or model-based control, can be used. 
     In the event that large surface area for thermal exchange between the gas and the thermal control medium leads to poor scalability of thermal duty, multiple heat exchangers can be used to increase and decrease contact area scalably so that flowrate and temperature of the thermal control medium remains within tolerance ranges. 
     At  512 , a temperature of the substrate is optionally sensed. A non-contact sensor such as an optical sensor can be used to sense the temperature of the substrate. The substrate temperature can be compared to a target to determine a deviation, and if the deviation is outside a tolerance range, the target temperature of the gas used for the gas cushion support can be adjusted to compensate. When the target temperature of the gas is adjusted, flowrate or temperature of the thermal control medium can be adjusted to bring the gas to the new target. 
     At  514 , a print material is deposited on the substrate. The print material is ejected from one or more dispensers in droplets sized from 5 μm to 50 μm, depending on the print job, toward the substrate as the substrate is scanned past the dispensers. By virtue of thermal control, the target locations for the droplets on the substrate remain near the designed positions so that the droplets arrive at the target locations within a tolerance range. 
       FIG.  6    is an isometric view of an inkjet printer  600  according to another embodiment. The inkjet printer  600  is similar to the inkjet printer  500 , but the inkjet printer  600  also includes separate thermal control for substrate edge gas. Two edge regions  602  and one central region  608  of the substrate support are identified by dotted lines. Each section of the substrate support  304 ,  306 , and  308  has a dedicated gas supply  610  for supplying gas to the edge regions  602  and the central region  608 . Each gas supply  610  has a blower  612  fluidly coupled to three flow control devices  614  to control gas flow to each edge region  602  and the central region  608  in the respective section of the substrate support. Each flow control device  614  is coupled to a passive heat exchanger  616  that serves as an ambient exchanger. The flow of gas from the heat exchangers  330 ,  340  and  360  is directed to a respective passive heat exchanger  616  to provide thermal exchange between thermally conditioned gas exiting the heat exchangers  330 ,  340  and  360  and gas from the blowers  612 . Compression of the gas by the blowers  612  adds some heat of compression to the gas. The passive heat exchangers  616  can be used to remove the heat of compression by thermal exchanged with the thermally conditioned gas exiting the heat exchangers  330 ,  340 , and  360 . The flow control devices  614  provide individual control of gas flow to each of the edge regions  602  and the central region  608  in each of the substrate support sections  304 ,  306 , and  308 . 
     Providing gas flow to the edge regions  602  and the central region  608  enables thermal control at substrate edges. Due to the geometric discontinuity at the substrate edge, specific gas flow may be needed in some cases to maintain substrate spacing at the edge of the substrate. The dedicated gas flow to the edge regions  602  enables edge spacing control to maintain edge spacing consistent with spacing of the rest of the substrate. Thermally controlling the gas supplied to the edge region of the substrate prevents any thermal excursions due to added heat from compression of the gas. Specific gas flow is provided to the central region  608  for edge control of substrates that do not extend the entire width of the substrate support. For example, when a substrate is processed in portrait format, the substrate edge may be positioned at the central region  608 . The specific gas flow to the central region  608  thus provides edge control of such substrates. Edge control gas can be provided to any combination of openings in the substrate support by providing plenums, for example metal or plastic boxes, attached to the lower surface of the substrate support and by plumbing control gas to the plenums in any desired configuration. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.