Abstract:
In some examples, a first heating stage heats a print medium to a first temperature in a printing region when printing latex ink on the print medium, and a curing heating stage heats, in a curing zone, the print medium to a curing temperature greater than the first temperature to cure the latex ink on the print medium. A cooling stage located between the first and curing heating stages cools the print medium by directing a first part of airflow from the cooling stage to a printing zone, the cooling performed after the print medium has been heated by the first heating stage and prior to heating of the print medium by the curing heating stage. A second part of the airflow is directed from the cooling stage to the curing zone.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 14/506,890, filed Oct. 6, 2014, which is a continuation of U.S. application Ser. No. 12/988,249, filed Oct. 15, 2010, now U.S. Pat. No. 8,894,303, which is a national stage application under 35 U.S.C. §371 of International Application No. PCT/EP2008/054751, filed Apr. 18, 2008, all applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a printing device for printing a latex ink on a printing medium. 
     The present invention further relates to a method for controlling such a printing device. 
     BACKGROUND 
     In the field of printing technology, a need exists for providing inks that allow for the generation of an image on a printing medium that retains a high image quality over a prolonged period of time, e.g. several years. Potentially interesting types of inks are water-based latex inks. An example of an ink comprising a latex binder is for instance given in PCT patent application WO 2007/112337 by the present applicant. The latex binder is added to the ink to bind the ink to the medium after printing. 
     In order to cure the latex in the ink following printing, the medium carrying the ink must be exposed to an elevated temperature. To this end, WO 2007/112337 proposes the use of any number of heated pick-up rollers, hot air fans or radiation devices. 
     In European patent application EP 1 403 341 A1, heating is employed during and after printing of a latex comprising ink on a non-absorbing substrate. The heating steps help spreading the ink over the non-absorbing substrate and accelerate the evaporation of the fluids in the ink solution. The heating steps during and after printing may be employed using light irradiation, a hot air source or an electrical heater. 
     However, heating a medium during or after reception of a water-based latex ink is not without problems. For instance, certain types of media may develop thermal marks when being exposed to excessive thermal flux. Moreover, the medium may exhibit significant thermal expansion, which is especially undesirable during printing because it can deteriorate the image quality. 
     Hence, there exists a need for a printing device that overcomes at least some of these problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein: 
         FIG. 1  schematically depicts a printing device according to an embodiment of the present invention; 
         FIG. 2  schematically depicts a temperature profile for a medium fed through the printing device of  FIG. 1 ; 
         FIG. 3  schematically depicts the stepped temperature profiles of the printing and curing heating stages according to an embodiment of the present invention; 
         FIG. 4  schematically depicts a printing zone state machine according to an embodiment of the present invention; 
         FIG. 5  schematically depicts a curing zone state machine according to an embodiment of the present invention; and 
         FIG. 6  is a flow diagram of a process of printing latex ink. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts. 
       FIG. 1  depicts a printing device  100  according to an embodiment of the present invention. The device  100  is arranged to feed a printing medium  110  over a print platen  120  in a direction indicated by the arrows over the pick-up rollers  105 . The rollers  105  are shown by way of non-limiting example only. The printing device  100  may have any suitable means for transporting the printing medium  110  over the print platen  120 . The printing medium  110  may be any medium suitable for receiving a latex ink. 
     The printing device  100  comprises a printing stage  155 . This may be any printing stage suitable for printing a latex ink on the printing medium  110 . For instance, the printing stage  155  comprises an ink jet printing head coupled to a reservoir for containing the latex ink. Many different types of ink jet printing heads are known to the skilled person, and such printing heads are therefore not described in further detail for reasons of brevity only. 
     The printing device  100  further comprises a first heating stage  140  for pre-heating the printing medium  110  before it enters the print platen  120 , i.e. the region under the printing stage  155 , and a second heating stage  150  for heating the printing medium  110  in the region of the print platen  120 , i.e. at the printing stage  155  under control of a controller  180 . The first heating stage  140  and the second heating stage  150  may be separate stages or a single stage arranged to cover more than one region of the printing device  100 . In case of the first heating stage  140  and the second heating stage  150  being separate regions, the controller  180  may be arranged to individually control the first heating stage  140  and the second heating stage  150 . In an embodiment, the printing device comprises a controller arrangement comprising separate controllers  180 , each arranged to control a separate heating stage of the printing device  100 . The separate controllers may be implemented as separate control stages of a single controller. 
     In an alternative embodiment of the printing device  100 , the first heating stage  140  is omitted. 
     The second heating stage  150  is arranged to ensure that the printing medium  110  is sufficiently warmed up to receive the latex ink from the printing stage  155 . The printing medium  110  must be warmed up to ensure that the fluids in the ink, e.g. water, are evaporated from the ink rapidly enough to prevent unwanted spreading of the ink on the printing medium  110 . In an embodiment, the printing medium  110  is heated to a temperature of around 55° C. by the second heating stage  150 . This temperature is sufficiently high to ensure effective evaporation of said fluids, and low enough to avoid thermal marking of the printing medium  110 . However, it will be appreciated that the exact temperature or temperature range is dependent of the type of media, e.g. a higher temperature may be used for media types that are more resistant to thermal marking. In an embodiment, the printing device comprises a user interface for specifying the media type, with the control arrangement comprising a look-up table with respective suitable heating stage output levels for a specified media type, such that the appropriate heat output level may be selected by a user. 
     Thermal marking may also occur when the printing medium  110  is exposed to a large thermal flux, i.e. a rapid change in temperature. In an embodiment, the printing device  100  is arranged to avoid the occurrence of such a large thermal flux. To this end, the first heating stage  140  is arranged to pre-heat the printing medium  110  in region A of the printing device to e.g. 40° C. Consequently, when the printing medium  110  reaches region B, i.e. the print platen  120 , the printing medium  110  only requires a relatively small additional heating step implemented by the second heating stage  150  in order to reach a temperature at which the printing medium  110  can receive the latex ink from the printing stage  155 . 
     The printing device  100  further comprises a third heating stage  170  for curing the latex in the image printed onto the printing medium  110 . The third heating stage is also controlled by the controller arrangement  180 . In an embodiment, the controller arrangement  180 , which will be described in more detail later, is arranged to operate the third heating stage  170  separately from the first heating stage  140  and/or the second heating stage  150 . The third heating element  170  is arranged to heat the printing medium  110  in region D of the printing device  100  to a temperature that is sufficient for curing the latex in the latex ink such that a protective latex layer is formed over the image on the printing medium  110 . In an embodiment, the third heating element  170  is arranged to heat the printing medium to a temperature around 95° C. Again, it should be understood that different temperatures may be selected for different media types. 
     In an embodiment, the printing device  100  further comprises a cooling stage  160  for cooling the printing medium  110  in a region C of the printing device  100 . The cooling stage  160  may be a fan-assisted air stream generator, which may be responsive to the controller  180 . The cooling stage  160  ensures that the thermal expansion of the printing medium  110  is well-controlled over the whole print zone of the printing device  100 , and assists in drying the latex ink deposited by the printing stage  155 . Moreover, the airflow aids the evaporation of ink solvents, e.g. water. To this end, at least a part of the airflow is arranged to flow parallel to the media towards the print zone in order to remove the water and avoid the ink spreading (bleed and coalescence). In an embodiment, a part of the airflow is also directed towards the curing zone to aid with the removal of solvents from the ink in this stage. Alternatively, a separate cooling stage may be used for this purpose. 
     The respective heating stages of the printing device  100  may be realized in any suitable way, e.g. by hot air fans or radiation devices. In an embodiment, the respective heating stages are realized by one or more infrared (IR) lamps per heating stage. 
     In an embodiment, the printing device  100  further comprises one or more temperature sensors  130  for monitoring the temperature of the printing medium  110  in the various regions of the print zone of the printing device  100 , such as the region C between the printing stage  155  and the curing zone D. The one or more temperature sensors  130  may be arranged to provide a measurement signal to the controller arrangement  180 , which may be arranged to adjust the temperature settings of the respective heating stages and/or the cooling stage in response to these measurement signals. In an embodiment, each heating stage controller is responsive to its own temperature sensor. The one or more temperature sensors  130  may be any suitable temperature sensor. 
     The controller  180  is arranged to ensure that the print medium  110  exhibits a well-controlled temperature profile over the print zone defined by regions A-D of the printing device  100 . Such a well-controlled temperature profile is important to avoid the occurrence of image artifacts caused by thermal marking and/or excessive thermal expansion of the printing medium  110 . An example of such a temperature profile is given in  FIG. 2 . 
     The plot in  FIG. 2  depicts the temperature of the printing medium  110  in ° C. as a function of the relative lateral distance of the printing medium  110  from the printing stage  155 . Upon entry of the print zone, the printing medium  110  is heated to around 40° C. in region A by the first heating stage  140 , after which the printing medium  110  is further heated to around 55° C. in region B by the second heating stage  150 . Next, the printing medium  110  is cooled down to around 40° C. in region C, e.g. by the fan-assisted cooling stage  160 . It is important to ensure that the temperature of the printing medium  110  upon entry and exit of the printing zone B shows at little variation as possible to avoid print quality artifacts in the image printed on the printing medium  110 , which may be caused by differential thermal expansion of the medium  110  in the printing zone B. Subsequently, the printing medium  110  is heated to around 95° C. in curing region D by the third heating stage  170 . 
     The printing device  100  may be arranged to feed the printing media  110  over the print zone in a continuous fashion, or may alternatively be arranged to feed the printing media  110  over the print zone in a stepwise fashion, wherein the printing media  110  is for instance temporarily stopped for receiving the latex ink from the printing stage  155  or for curing the latex ink by the third heating stage  170 . The printing media  110  may further comprise unprinted regions, which exhibit a different tolerance to exposure to an elevated temperature than the regions of the printing medium  110  carrying a latex ink. 
     In an embodiment, the controller arrangement  180  is arranged to control the heating stages of the printing device  100  such that a distinction is made between heating the printing medium  110  during printing and curing an image on the printing medium  110  and heating the printing medium  110  when the printing device  100  is not generating an image onto the printing medium. In the printing/curing mode, the printing device  100  ensures that the printing medium  110  is fed continuously through the printing device, which ensures that the exposure of the printing medium  110  to each of the heating stages does not exceed a certain amount of time, and, as a consequence, a certain amount of thermal exposure. 
     However, when a printing/curing job is completed, the printing medium  110  may remain stationary in the printing device  100 , in which case prolonged exposure to one of the heating stages may cause thermal marking to the printing medium  110 . The controller arrangement  180 , e.g. the individual controllers of the respective heating stages are therefore arranged to reduce the heat output of the heating stage as soon as the job of that stage is finished, e.g. upon completion of a printing job in the printing zone and upon completion of a curing job in the curing zone. The respective heating stages are not completely switched off to avoid excessive start-up times of the respective heating stages upon commencing a new job. Moreover, a rapid change in temperature of the printing medium  110  could cause rapid thermal expansion of the printing medium, thereby increasing the risk of thermal damage to the printing medium  110 . 
       FIG. 3  depicts the respective heating states of the second heating stage  150  (solid line) and the third heating stage  170  (dashed line) in ° C. as a function of time. In this embodiment, the first heating stage  140  and the second heating stage  150  are controlled by separate controllers  180   
     Table I gives an overview of the various heating states of the second heating stage  150  and the third heating stage  170  shown in  FIG. 3 . 
     
       
         
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Stage 150 state 
                   
                 Stage 170 state 
               
               
                   
               
             
             
               
                 301 
                 OFF 
                 351 
                 OFF 
               
               
                 302 
                 PRINTING 
                 352 
                 READY-TO-CURE 
               
               
                 303 
                 STAND-BY 
                 353 
                 CURING 
               
               
                   
                   
                 354 
                 STAND-BY 
               
               
                   
               
             
          
         
       
     
     Upon transition  310 , which is typically triggered by the initiation a print instruction received by the printing device  100  from an external source, the second heating stage  150  switches from its OFF state to its PRINTING state, causing the second heating stage  150  to heat the printing medium  110  to a temperature suitable for printing the latex ink onto the printing medium  110 , e.g. 55° C., and the third heating stage  170  switches to its READY-TO-CURE state, in which the third heating stage  170  produces a heat output that does not damage the printing medium  110  during prolonged exposure to the heating stage  170 . The temperature of the printing medium  110  in the curing region D in this READY-TO-CURE state typically is an intermediate temperature that is lower than the temperature of the printing medium  110  during curing but higher than the temperature of the printing medium  110  in the OFF state of the third heating stage  170 . 
     The READY-TO-CURE state further ensures that the third heating stage  170  can be quickly switched to its CURING state while avoiding a large thermal flux, thus reducing the risk of thermal damage to the printing medium  110 . 
     Upon the latex ink carrying printing medium  110  reaching the curing zone D, as indicated by the transition  315 , the controller  180  switches the third heating stage  170  from the READY-TO-CURE state to the CURING state, in which the printing medium  110  is heated to a temperature at which the latex in the ink is cured to form a protective layer over the printed image, e.g. 95° C. 
     Simultaneously, upon completion of printing the image on the printing medium  110 , the controller  180  switches the second heating stage  150  from its PRINTING state to a STANDBY state, as indicated by transition  320 . In the STANDBY state, the second heating stage  150  is arranged to heat the printing medium  110  to an intermediate temperature that is that is lower than the temperature of the printing medium  110  during printing but higher than the temperature of the printing medium  110  in the OFF state of the second heating stage  150  in order to protect non-printed media from the formation of thermal artifacts thereon. 
     In an embodiment, the controller  180  of the curing heating stage  170  is configured to engage the CURING STATE a predefined amount of time after engaging the PRINTING state. The predefined amount of time is based on the distance between the printing stage  155  and the third heating stage  170  and the propagation speed of the printing medium  110  over the printing zone of the printing device  100 . 
     The third heating stage  170  may also be switched to a STANDBY state upon completion of the curing of the printed image on the printing medium  110 , as indicated by the transition  325 . The STANDBY states ensure that the printing medium  110  is not exposed to excessive temperatures whilst being stationary in the printing device  100 , this avoiding the formation of thermal artifacts on non-printed regions of the printing medium  110 , and is not exposed to an excessive thermal flux during initiation of the printing of a next image, as indicated by transition  330 . Upon power-down of the printing device  100 , the second heating stage  150  and the third heating stage  170  return to their OFF states, as shown by transition  340 . 
     In an embodiment, the respective controller stages  180  each may comprise a state machine to implement the control mechanism shown in  FIG. 3 . Since the implementation of a state machine in hardware or software may be realized in many ways that all require routine skill for the skilled practitioner, a detailed description of the implementation details of such state machines is omitted for reasons of brevity only. 
       FIG. 4  depicts an embodiment of a state machine  400  for controlling the second heating stage  150 . Table II gives an overview of the states in this state machine. 
     
       
         
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 State Number 
                 State Name 
               
               
                   
               
             
             
               
                 410 
                 Init 
               
               
                 420 
                 Off 
               
               
                 425 
                 Warming up for Standby 
               
               
                 430 
                 Warming up for Printing 
               
               
                 440 
                 Printing 
               
               
                 450 
                 Cooling down to Standby 
               
               
                 460 
                 Standby 
               
               
                 470 
                 Cooling down to Off 
               
               
                   
               
             
          
         
       
     
     The state machine  400  starts in initial state  410 , after which the state machine  400  proceeds to state  420  in case the temperature of the printing medium  110  is lower than a printing medium threshold temperature defined for state  410 , which corresponds with state  301  in  FIG. 3 . From state Off, the state machine  400  may proceed to state  425  in case activation of the printing device  100  does not coincide with a print request, or to state  430  in case the activation of the printing device  100  does coincide with a print request. State  430  corresponds with the transition from state  301  to state  302  in  FIG. 3 . 
     Once the second printing stage  150  has warmed up, the state machine progresses to state  440 , which corresponds with state  302  in  FIG. 3 . The transition from state  430  to state  440  may occur after a predefined period of time or after receiving a signal from a temperature sensor indicating that the required temperature has been reached. From state  440 , the state machine  400  may proceed to state  450 , which corresponds with the transition from state  302  to  303  in  FIG. 3 , upon completion of printing the image on the printing medium  110  or to state  470  upon the printing device  100  being switched off. 
     From state  450 , the state machine  400  may proceed to state  460 , which corresponds to state  303  in  FIG. 3  upon completion of the cooling down cycle. This transition may occur after a predefined period of time or after receiving a signal from a temperature sensor indicating that the required temperature has been reached. Alternatively, the state machine  400  may step from state  450  to state  430  in case of the reception of a new printing instruction by the printing device  100 . 
     From standby state  460 , the state machine  400  may revert back to state  430  in case of the reception of a new printing instruction by the printing device  100 . The state machine  400  may also proceed to state  470  corresponding to the transition from state  303  to  301  in  FIG. 3 . The transition to state  470  may be invoked by the printing device  100  being switched to an idle mode, e.g. powered-down mode. 
     In case the temperature of the printing medium  110  exceeds the threshold temperature defined for state  410  but does not exceed its threshold temperature defined for standby state  460 , the state machine  400  may step from state  410  to  460 . The threshold temperature for the standby state is chosen such that an unprinted printing medium  110  is not at risk of experiencing thermal damage when being exposed to the standby temperature. 
     In case the temperature of the printing medium  110  exceeds the threshold temperature defined for state  410  as well as exceeds its threshold temperature defined for standby state  460 , the printing medium  110  is at risk of experiencing thermal damage. Consequently, the state machine  400  is arranged to step from state  410  to  450  in order to cool down the printing medium  110 , which may trigger the cooling stage  160  to be activated. 
     In an embodiment, the controller  180  may be overruled by a manual instruction, causing the state machine  400  to step from state  420  directly to state  440 . 
       FIG. 5  depicts an embodiment of a state machine  500  for controlling the third heating stage  150 . Table II gives an overview of the states in this state machine. 
     
       
         
               
               
             
           
               
                 TABLE III 
               
               
                   
               
               
                 State Number 
                 State Name 
               
               
                   
               
             
             
               
                 510 
                 Init 
               
               
                 520 
                 Off 
               
               
                 525 
                 Warming up for Standby 
               
               
                 530 
                 Warming up for Ready to cure 
               
               
                 540 
                 Ready to cure 
               
               
                 550 
                 Warming up for curing 
               
               
                 560 
                 Curing 
               
               
                 570 
                 Cooling down to Standby 
               
               
                 580 
                 Standby 
               
               
                 590 
                 Cooling down to Off 
               
               
                   
               
             
          
         
       
     
     The state machine  500  starts in initial state  510 , after which the state machine  500  proceeds to state  520  in case the temperature of the printing medium  110  is lower than a printing medium threshold temperature defined for state  510 , which corresponds with state  351  in  FIG. 3 . From state Off, the state machine  500  may proceed to state  525  in case activation of the printing device  100  does not coincide with a print request, which means that no curing is (immediately) required, or to state  530  in case the activation of the printing device  100  does coincide with a print request, and the third heating stage  170  is to be brought into a ready-to-cure state. State  430  corresponds with the transition from state  351  to state  352  in  FIG. 3 . 
     Once the third printing stage  170  has reached its ready-to-cure temperature, the state machine  500  progresses to state  540 , which corresponds with state  352  in  FIG. 3 . The transition from state  530  to state  540  may occur after a predefined period of time or after receiving a signal from a temperature sensor indicating that the required temperature has been reached. 
     From state  540 , the state machine  500  may proceed to state  550 , which corresponds with the transition from state  352  to  353  in  FIG. 3 , upon an indication that a printed printing medium  110  is approaching the third heating stage  170 . Upon reaching the curing temperature, the state machine  500  progresses to state  560 , in which the latex in the printed medium is cured. Upon reaching the end of the printed region of the printing medium  110 , e.g. the end of the document, the state machine  500  progresses to state  570 , in which the third heating stage  170  is cooled down such that the unprinted printing medium  110  is not exposed to a temperature that may cause thermal damage to the unprinted printing medium  110 . State  570  corresponds with the transition from state  353  to  354  in  FIG. 3 . 
     When the third heating stage  170  is sufficiently cooled down, the state machine  500  progresses to state  580 , which corresponds with state  354  in  FIG. 3 . From this standby state, the state machine  500  may proceed to state  590  in case the printing device is switched off, or may revert to state  530  in case of a new curing task. 
     Other transitions in the state machine  500  are also feasible. For instance, the state machine  500  may progress from any of states  540 ,  550  and  560  to state  590  in case the printing device  100  is switched off whilst the state machine  500  resides in any of the states  540 ,  550  and  560 . Similarly, the state machine  500  may progress from states  540  and  550  to state  570  in case the printing device  100  is switched to a standby mode whilst the state machine  500  resides in any of the states  540  and  550 . This may for instance occur when a print request is cancelled. 
     In case the temperature of the printing medium  110  exceeds the threshold temperature defined for state  510  but does not exceed its threshold temperature defined for standby state  580 , the state machine  500  may step from initial state  510  to  580 . The threshold temperature for the standby state  580  is chosen such that an unprinted printing medium  110  is not at risk of experiencing thermal damage when being exposed to the standby temperature. 
     In case the temperature of the printing medium  110  exceeds the threshold temperature defined for off state  510  as well as exceeds its threshold temperature defined for standby state  580 , the printing medium  110  is at risk of experiencing thermal damage. Consequently, the state machine  500  is arranged to step from state  510  to  570  in order to cool down the printing medium  110 , which may trigger the cooling stage  160  to be activated. 
     In an embodiment, the controller(s)  180  may be overruled by a manual instruction, causing the state machine  500  to step from state  510  directly to state  560 . 
     The state machines  400  and  500  implement different aspects of the temperature control method of the present invention. It will be appreciated that  FIGS. 4 and 5  depict simplified versions of the state machines  400  and  500 . For instance, exceptions have not been shown for reasons of clarity only. Such exceptions may for instance occur if a state has a time-out limit, with the state machine progressing to an error state or another predefined state upon exceeding the time-out limit of the state in which the state machine resides. 
     It will further be appreciated that although the state machines  400  and  500  are shown as independent state machines, certain states and transitions in these state machines are interrelated. For instance, as shown in  FIG. 3 , the transition  310  (exiting the OFF state) occurs at the same time for both the second heating stage  150  and the third heating stage  170 , which means that the state machines for these heating stages enter respective states  420  and  520  at the same time. Similarly, the state machine  500  will enter curing state  560  a predefined amount of time after the state machine  400  entering the printing state  450  corresponding with the predefined amount of time it takes the printing medium  110  to propagate from region B to region D in the printing device  100 . 
     By entering the heating stages  150  and  170  (and  140  if separately controlled) into a pre-heating state such as standby states  460  and  580  respectively, the heating stages can be quickly brought to the required temperature for printing and curing. This facilitates the use of relatively cheap heating elements such as IR lamps, which have a long lifetime and require less power to operate than alternative heating elements such as fast shutter-based designs. 
     The one or more controllers  180  may be implemented in software on a processor such as a central processing unit of the printing device  100 . The controller software may be made available on any suitable computer-readable data carrier. 
       FIG. 6  is a flow diagram of a process of printing latex ink on a printing medium. The printing medium is heated (at  602 ) to a first temperature in a printing region when printing latex ink on the printing medium. The printing medium is heated (at  604 ) to a second temperature in a curing region to cure the latex ink on the printing medium. The printing medium is heated (at  606 ) to a first further temperature in the printing region in a non-printing mode, where the first further temperature is lower than the first temperature. The printing medium is heated (at  608 ) to a second further temperature in the curing region in a non-curing mode, where the second further temperature is lower than the second temperature. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.