WO2020131023A1

WO2020131023A1 - Pulse width modulation value calculations

Info

Publication number: WO2020131023A1
Application number: PCT/US2018/066162
Authority: WO
Inventors: Daniel James MAGNUSSON; Robert Yraceburu; Devin Scott Uehling; Vladislav SHAPOVAL
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2018-12-18
Filing date: 2018-12-18
Publication date: 2020-06-25

Abstract

In some examples, a device for pulse width modulation value calculations can include a non-transitory machine readable medium storing instructions executable by a processing resource to: determine when a start temperature of a heated pressure roller is above a threshold temperature, calculate a pulse width modulation (PWM) value for the heated pressure roller based on a set point for the heated pressure roller and a difference between the start temperature and the threshold temperature, and apply the calculated PWM value as a seeding value for the heated pressure roller when the start temperature is above the threshold temperature.

Description

PULSE WIDTH MODULATION VALUE CALCULATIONS

Background

[0001] Imaging devices, such as printers and scanners, may be used for transferring print data on to a medium, such as paper. The print data may include, for example, a picture or text or a combination thereof and may be received from a computing device. The imaging device may generate an image by processing pixels each representing an assigned tone to create a halftone image.

Brief Description of the Drawings

[0002] Figure 1 illustrates a memory resource storing instructions for pulse width modulation value calculations according to an example

[0003] Figure 2 is a block diagram of a controller including processing circuitry suitable for pulse width modulation value calculations according to an example.

[0004] Figure 3 is a block diagram of an imaging device including a memory resource storing instructions for pulse width modulation value calculations according to an example

[0005] Figure 4 illustrates a graph for pulse width modulation value calculations according to an example

[0006] Figure 5 is a process for pulse width modulation value calculations according to an example.

Detailed Description

[0007] In some examples, an imaging system can include an inkjet printing device in some examples, the inkjet printing device can deposit quantifies of a print substance on a physical medium in some examples, the print substance can create a curl, and/or cockle in the physical medium when the print substance deposited on the physical medium is not completely dry. In some examples, a number of physical properties of the physical medium can be changed when the print substance is deposited by the imaging system. For example, the stiffness of the physical medium can be changed when the print substance includes fluid droplets. In some examples, the physical medium with deposited print substance that is not completely dry can be referred to as partially dried media

[0008] The curl, cockle, and/or other physical properties that change due to the print substance can make finishing processes difficult. As used herein, a finishing process can include a process performed by the imaging system or finisher device after the print substance is deposited on the physical medium. The partially dried media can provide difficulties when stacking, aligning, and/or finishing. For example, the partially dried media can have distorted properties such as a curl, a cockle, a reduction in stiffness, increased surface roughness, extruding fibers from the surface, misaligned fibers, and/or increased sheet to sheet friction of the media. In some examples, these distorted properties can be caused by printing fluid deposited on the physical medium and the physical medium absorbing the printing fluid. For example, the print substance can be in a liquid state that can be absorbed by a physical medium such as paper. In this example, the liquid state of the print substance can cause the distorted properties of the partially dried media in a similar way that other liquids may distort the properties of the physical medium.

[0009] In some examples, a drying zone of an imaging device can be utilized to remove the liquid and/or distorted properties from the partially dried inkjet media. The drying zone can include, but is not limited to, a number of air flow devices, pressure rollers, heated rollers, and/or heated pressure rollers. In some examples, a heated pressure roller of the drying zone can be utilized to remove the distorted properties from the physical medium or partially dried medium. For example, the heated pressure roller can be utilized to apply pressure to a surface of the partially dried media and apply heat to the surface of the partially dried media. In this example, the applied heat and pressure can remove or substantially remove the distorted properties of the partially dried media.

[0010] In some examples, the drying zone or a component of the drying zone can include a heat source (e.g., heat generating device, halogen lamp, etc ) that can be utilized to increase a temperature of the drying zone and/or a device within the drying zone such as a heated pressure roller. For example, the heat source can include a halogen lamp that can generate heat within a belt roller of a heated pressure roller system. In some examples, the heat source can utilize a set point temperature for a particular print job.

[0011] For example, the set point temperature can be utilized to remove the distorted properties for the partially dried inkjet media generated by a particular print job. In this example, the set point temperature can be based on a quantity of print substance deposited on the print media. For example, a first print job with a first quantity of print substance deposited on a print media can utilize a first set point temperature to remove distorted properties and a second print job with a second quantity of print substance deposited on the print media can utilize a second set point temperature in this example, a greater quantity of print substance deposited on the print media can correspond to a greater set point temperature. Thus, when the first quantity of print substance is greater than the second quantity of print substance, the first set point temperature can be greater than the second set point temperature in other examples, when there is a greater quantity of print substance, the speed of the heated pressure roller can be altered to accommodate for the greater quantity of print substance. In some examples, the speed of the print job can be adjusted and the set point temperature can be adjusted proportionally.

[0012] In some examples, the imaging device can have power restrictions. For example, the imaging device can have a maximum quantity of power that can be utilized during operation. In this example, the maximum quantity of power for the imaging device can also be restricted by regulatory agencies. In some examples, generating heat that exceeds the set point temperature for a print job can utilize a greater quantity of power than generating heat up to the set point. Thus, preventing a temperature of the drying zone and/or heated pressure roller of the imaging device can allow the imaging device to utilize a relatively lower quantity of power in some examples, temperatures that exceed the set point temperature can damage parts and/or distort print media due to over-drying. [0013] In some examples, the Imaging device can utilize a RID mode that can utilize a pulse width modulation (PWM) value (e.g., starting PWM value, starting value, seeding PWM value, etc.) for increasing a current temperature of the drying zone and/or heated pressure roller. As used herein, a PWM value includes a starting value for a PWM controller that can be utilized during a RID mode of an imaging device. In some examples, a PWM value can be proportional to a rate of temperature increase and can be utilized to avoid exceeding the set point temperature. In some examples, the PWM value can be a seeding PWM value that can be calculated utilizing a current temperature of the drying zone and/or heated pressure roller, a maximum PWM value, a minimum PWM value, and/or a temperature set point for a particular print job. in this way, the seeding PWM value can be Implemented at the beginning of a RID mode and provide more accurate temperature and power control, provide less temperature over-shoot, reduce media jams, reduce media damage, provide better page to page alignment within a finisher device, lower thermal stress on parts of the imaging device, and/or lower a risk of tripping thermal fuses/cutoffs.

[0014] As such, the disclosure is directed to pulse width modulation value calculations. For example, a device for pulse width modulation value calculations can include a non-iransiiory machine readable medium storing instructions executable by a processing resource to: determine when a start temperature of a heated pressure roller is above a threshold temperature, calculate a pulse width modulation (PWM) value for the heated pressure roller based on a set point for the heated pressure roller and a difference between the start temperature and the threshold temperature, and apply the calculated PWM value as a seeding value for the heated pressure roller when the start temperature is above the threshold temperature.

[0015] Figure 1 illustrates a memory resource 102 storing instructions for pulse width modulation value calculations according to an example. In some examples, the memory resource 102 can be utilized to store instructions 104, 106, 108 that can be executed by a processing resource. For example, the memory resource 102 may be communicatively coupled to a processing resource which may be a central processing unit (CPU), a semiconductor-based microprocessor, and/or other hardware devices suitable for retrieval and execution of instructions 104, 106, 108 stored in the memory resource 102 (e.g., in a non- transitory computer readable medium). The example processing resource may fetch, decode, and execute instructions. As an alternative, or in addition to, retrieving and executing instructions, the example processor may include an electronic circuit that may include electronic components for performing the functionality of executed instructions.

[0016] In some examples, the processing resource may be a plurality of hardware processing units that may cause machine-readable instructions to be executed. The processing resource may include central processing units (CPUs) among other types of processing units. The memory resource 102 may be any type of volatile or non-voiatile memory or storage, such as random- access memory (RAM), flash memory, storage volumes, a hard disk, or a combination thereof.

[0017] The memory resource 102 may store instructions thereon, such as instructions 104, 106, 108. When executed by the processing resource, the instructions may cause an imaging device to perform specific tasks and/or functions. For example, the memory resource 102 may store instructions 104 which may be executed by the processing resource to cause the imaging device to determine a start temperature for a heated pressure roller in some examples, the determined start temperature can be utilized to calculate a seeding pulse width modulation (PWM) value to be utilized to alter a

temperature of the heated pressure roller from a current temperature to a set temperature for a particular print job being performed by the imaging device.

[0018] The memory resource 102 may store instructions 104 which may be executed by a processing resource to determine that a start temperature of a heated pressure roller is above a threshold temperature in some examples, the memory resource 102 can receive a temperature value for a plurality of devices associated with an imaging device. For example, the memory resource can be communicatively coupled to a plurality of temperature sensors that are utilized to monitor a temperature of a corresponding device or area of the imaging device. In some examples, the threshold temperature is a temperature that when exceeded initiates a proportional integral derivative mode for the heated pressure roller. The RID range can be a range of temperatures that a RID mode utilizes. For example, the RID range can be a range of temperatures between a threshold temperature and a set point temperature for a heated pressure roller.

[0019] In some examples, the temperature sensors can be utilized to monitor a temperature of a drying zone of an imaging device. For example, a temperature sensor can be utilized to monitor a temperature of a heated pressure roller. In this example, the temperature sensor can be utilized to determine when the heated pressure roller Is at or near a set point temperature. The set point temperature can be a temperature that is set for a particular print job to remove potential distorted properties caused by depositing a print substance on the print media in some examples, the set point temperature can be based on a quantity of print substance that is deposited on the print media and/or a predicted level of distorted properties of the partially dried inkjet media. That is, the heated pressure roller may be set to a temperature (e.g., utilize a set point temperature, etc.) that is capable of reducing or removing distorted properties from the partially dried inkjet media to a particular level (e.g., acceptable level, etc.).

[0020] In some examples, a print job can be initiated for the imaging device when the temperature of the drying zone and/or heated pressure roller is relatively higher than room temperature. For example, the print job can be initiated shortly after a previous print job such that the temperature of the drying zone and/or heated pressure roller has residual heat from the previous print job. in some examples, the monitored temperature at a start of the print job can be above a threshold temperature value.

[0021] As used herein, a threshold temperature value can be a particular temperature that can trigger an event. For example, the threshold temperature can be a temperature when a heat source associated with the drying zone is started in a ramp up state if the temperature is below the temperature threshold, or a RID state if the temperature is above the temperature threshold in some examples, the ramp up state can be a state when the heat source is generating a maximum or relatively large quantity of heat to bring the temperature of the drying zone up toward the set point in a relatively small quantity of time. In some examples, the heat source can alter from the ramp up state to the RID state when the monitored temperature exceeds a threshold temperature to prevent the monitored temperature of the drying zone from exceeding the set point temperature, which can waste electrical power of the imaging device and/or generate errors for the print job. in some examples, the threshold temperature for the heat source to alter from the ramp up state to the FID state may be a different threshold temperature than a threshold temperature for the heat source at a start of the print job. For example, a first threshold of a set point minus 25 degrees can be utilized at the start of the job and a second threshold of a set point minus 5 degrees can be utilized when the print job starts in the ramp up state and alters to the RID state

[0022] When the monitored temperature of the drying zone is above the threshold temperature at the start of the print job, the RID state can be initiated at the start of the print job. In these examples, the RID state can utilize a seeding PWM value (e.g., Initial PWM value, etc.) to more precisely bring the temperature to the set point temperature of the print job. As described herein, a PWM value for the ramp up state and/or seeding PWM value for the RID state includes a starting value for a PWM controller and/or RID controller to generate later PWM values that can be utilized to control electrical power provided to a device such as a heat source. For example, the seeding PWM value can be a starting PWM value utilized by a PWM controller to bring the temperature up to the set point value more quickly without exceeding the set point temperature compared to utilizing a ramp up or minimum PWM value when the monitored temperature is at or near the threshold temperature value as a starting PWM value utilized by the PWM controller. In this example, the PWM controller can utilize the seeding PWM value as a start value for calculating later PWM values based on a received response signal such as a current temperature signal for a drying zone and/or heated pressure roller. That is, a first PWM value can be utilized as a starting PWM value for the PWM controller during the ramp up state to the RID state and a second PWM value (e.g., seeding PWM value) can be utilized as a starting PWM value when the monitored temperature exceeds the threshold temperature at a start time of a print job. Thus, when the starting temperature of the drying zone and/or heated pressure roller is above the threshold temperature, a seeding PWIVi value for the drying zone and/or heated pressure roller can be calculated based on a number of factors. In some examples, the first PWM value that is utilized as a starting PWM value for the PWM controller during the ramp up state can be a max PWM value that doesn’t change until the imaging device alters from the ramp up state to the PID state [0023] The memory resource 102 may store instructions 106 which may be executed by a processing resource to calculate a pulse width modulation (PWM) value for the heated pressure roller based on a set point for the heated pressure roller and a difference between the start temperature and the threshold temperature. In some examples, the PWM value that is calculated can be a seeding PWM value that can be utilized to bring the temperature from the current temperature to a set point temperature. As described herein, the PWIVi value can be based on the threshold temperature, a maximum PWIVI value (e.g , ramp up value, etc.) a minimum PWIVI value, the set point temperature for a particular print job, a difference between a current temperature and a set point temperature for the particular print job, a PWM value from a previous print job, and/or a difference between a current temperature and the threshold

temperature. For example, the seeding PWM value can be calculated utilizing Expression 1.

PWMseed ~ (PWMprev ⁺ (PWM max ~ PWMprev)) X (iTsei - Tsiari) / Tset ~~ PI Dthreshold))

Expression 1

[0024] Expression 1 illustrates an example for calculating a seeding PWM value (PWMseed) that can be utilized when the current temperature or starting temperature (Tstart) of the drying zone and/or heated pressure roller is above a threshold temperature or PI D threshold value (PI Dthreshold). In some examples, the threshold temperature and/or the PI D threshold value can be a temperature value that alters a state of the imaging device from a ramp up state to a PI D state. That is, a current temperature below the PI D threshold value can put the imaging device in a ramp up state and a current temperature above the PI D threshold value can put the imaging device in a PI D state. [0025] Expression 1 can utilize a previous PWM value (PWM_prev) from a previous print job. In some example, the previous PW!Vi value can be a PWM value that was utilized for a print job that was performed immediately prior to a current print job. In some examples, the print job that was performed immediately prior to the current print job can cause the current temperature or start temperature (T s_tar_t) to be above the PID threshold value. Expression 1 can utilize a maximum PWM value (PWM max) for a PWM controller to calculate the seeding PWM value (PWM see_d). In some examples, the maximum PWM value can be limited by the PWM controller and/or the imaging system. In some examples, the calculated PWM value is proportional to a difference between the start temperature and the set point for the heated pressure roller. That is, the further away the start temperature or current temperature is from the set point (e.g., greater difference between the start temperature and the set point temperature), the greater the calculated PWM value. In addition, the lower the difference between the start temperature and the set point temperature, the smaller the calculated PWM value.

[0026] In some examples, the memory resource 102 can include instructions to retrieve a minimum PWM value for the heated pressure roller when a previous PWM value is not available in some examples, a previous PWM value for a previous print job may not be available to compare to the calculated PWM value. In these examples, the calculated PV /M value (e.g., seeding PWM value) is between a minimum PWM value and a maximum PWM value for the PID mode of the controller. Thus, in these examples, the calculated PWM value is selected and applied in some examples, the minimum PWM value can be calculated based on a voltage applied to a heat source of the heated pressure roller (e.g., minimum PWM value = 20 x (115

Voits/Measured Voltage)²). In this example, 20 would be a coefficient representing the steady state PWM needed for a given system to maintain a given setpoint temperature at 115 Volts.

[0027] In some examples, the maximum PWM value for the PID mode of the controller is the PWM value utilized in a ramp mode and the minimum PWM value for the PID mode of the controller is a PWM value to maintain a set point temperature after a sustained time at the set point temperature. That is, the maximum PWM value can be utilized during a ramp mode or until the temperature of the drying zone and/or heated pressure roller exceeds a threshold temperature (e.g., set point minus 5 degrees, threshold temperature utilized when ramp up state is utilized at the start of a print job, etc.). In some examples, a RID control loop can be utilized to maintain the set point temperature through a process of sensing the current temperature, comparing the current temperature to the set point temperature, respond to any errors that may occur by reacting, and alter a PWM signal to make any corrections (e.g., altering the PWM value, having the heat source be activated more often, having the heat source be activated less often, etc.) in response to a difference between the current temperature and the set point temperature.

[0028] The memory resource 102 may store instructions 108 which may be executed by a processing resource to apply the calculated PWM value as a seeding value for the heated pressure roller in response to a determination that the start temperature is above the threshold temperature. As described herein, the seeding value can be calculated utilizing Expression 1. The seeding PWM value can be a starting value for a PWM controller to apply to a heat source and/or a plurality of heat sources to alter the temperature of the drying zone and/or heated pressure roller from a current temperature to a set point temperature. In addition, the seeding PWM value can be utilized to minimize temperature overshoots of the drying zone and/or heated pressure roiier (e.g., temperatures that significantly exceed the set point temperature, temperatures that exceed the set point temperature by a threshold temperature value above the set point temperature, etc.), which can increase power usage and/or potentially damage print media moving through the drying zone and/or heated pressure roller.

[0029] Figure 2 is a block diagram of a controller 210 including

processing resource 212 suitable for pulse width modulation value calculations according to an example. Figure 2 Illustrates an example controller 210, including a processing resource 212 and a memory resource 202. For example, the controller 210 may include a processing resource 212 which may be a central processing unit (CPU), a semiconductor-based microprocessor, and/or other hardware devices suitable for retrieval and execution of instructions stored in a memory resource 202 (e.g., in a non-transitory computer readable medium).

[0030] The memory resource 202 may store instructions 214 which may be executed by the processing resource 212 to cause the controller 210 to determine that a current temperature of the drying zone of an imaging device is above a threshold temperature of a set point temperature for the drying zone.

As described herein, a drying zone and/or a heated pressure roller can include temperature sensors that can monitor a temperature of an area, a device, and/or a surface in some examples, a temperature sensor can be utilized to determine a current temperature of the drying zone. In some examples, the current temperature can be determined to be a temperature at a particular point in time. For example, the current temperature can be a start temperature for a print job. In this example, the start temperature can be a temperature of the drying zone and/or heated pressure roller when a print job is started and/or when the imaging device receives instructions to perform a print job.

[0031] In some examples, the current temperature can be a temperature value after a previous print job has completed. That is, the current temperature can be an actual temperature of the drying zone once the previous print job has been completed and a current print job is initiated in some examples, the current temperature can be above a threshold temperature. As described herein, the threshold temperature can be a temperature when the imaging device starts in a RID state rather than a ramp up state. In some examples, the threshold temperature can be based on a set point temperature for a particular print job. For example, the threshold temperature can be the set point temperature minus 25 degrees. In one example, when the set point temperature is 110 degrees Celsius (C), the corresponding threshold temperature can be 85 degrees C. Thus, in this example, the current temperature can be determined to be above the threshold or within a threshold range when the current temperature is between 110 degrees and 85 degrees C.

[0032] The memory resource 202 may store instructions 216 which may be executed by the processing resource 212 to cause the controller 210 to calculate a seeding pulse width modulation (PWM) value for a proportional- integral-derivative (RID) mode of the controller for the drying zone based on a linear interpolation between the set point temperature and the threshold temperature. In some examples, the set point temperature can be based on features of the print job (e.g., quantity of printing substance deposited on the print media, size of the print media, etc.) in some examples, the seeding PW!VI value for the RID mode can be based on a linear interpolation between the set point temperature for the print job and the determined threshold temperature, which can be based on the set point temperature. As used herein, linear interpolation includes curve setting methods that utilize data points to fill in additional data points based on a determined curve from real data points. In some examples, the linear interpolation can be stored in the memory resource 202 such that received values can be identified and a seeding PWM value can be calculated. For example, Expression 1 can be utilized as a function for linear interpolation to calculate the seeding PWM value

[0033] The memory resource 202 may store instructions 218 which may be executed by the processing resource 212 to cause the controller 210 to apply the seeding PWM value to alter a temperature of the drying zone from the current temperature to the set point temperature. As described herein, the calculated seeding PWM value can be an initial value utilized by a PWM controller to apply a particular voltage at a particular frequency or a particular percentage of time on versus time off in a given time period to a heat source in order to increase a temperature of the drying zone and/or heated pressure roller to the set point temperature.

[0034] Figure 3 is a block diagram of an imaging device 320 including a memory resource 302 storing instructions for pulse width modulation value calculations according to an example. Figure 3 illustrates an imaging device 320. The imaging device 320 can be an inkjet imaging device. As used herein, an inkjet imaging device can deposit a print substance (e.g., liquid ink, etc.) on a print media (e.g., paper, etc.). In some examples, the print substance can be absorbed into the print media, which can cause distorted properties (e.g., curl, cockle, etc.). In some examples, the imaging device 320 can utilize a drying zone 322 to remove excess moisture and/or distorted properties from partially dried inkjet media (e.g., media with deposited print substance from the imaging device 320, etc.).

[0035] Figure 3 illustrates an example imaging device 320 that includes a drying zone 322 that includes a heated pressure roller 324. In some examples, the heated pressure roller 324 can be utilized to remove distorted properties from partially dried inkjet media by applying heat and/or pressure on a surface of the partially dried inkjet media in some examples, the heated pressure roller 324 can include a first roller 326 (e.g., top roller, pressure roller, etc.) that can be a solid cylindrical roller that can apply pressure to a first side (e.g., top side, etc.) of the partially dried inkjet media. In some examples, the heated pressure roller 324 can include a second roller 328 (e.g., bottom roller, belt roller, heated belt roller, etc.) that can apply heat to a second side (e.g., bottom side, etc.) of the partially dried inkjet media. In some examples, the second roller 328 can include a heat source positioned within the second roller 328 to receive power controlled by a PWM signal from a PWM controller to generate a corresponding quantity of heat based on the received PWM signal. In some examples, the drying zone 322 can be communicatively coupled to a computing device or controller that includes a memory resource 302 and/or processing resource 312. For example, a communication channel 330 can allow a controller (e.g., PWM controller, computing device, etc.) to apply a PWM signal through a power control module to heat sources of the drying zone 322 (e.g., heat source in first roller 326, heat source in second roller 328, etc.).

[0036] Figure 3 illustrates an example memory resource 302 storing instructions executable by a processing resource 312 to cause the imaging device 320 and/or the drying zone 322 to perform particular functions. For example, the imaging device 320 may include a processing resource 312 which may be a central processing unit (CPU), a semiconductor-based microprocessor, and/or other hardware devices suitable for retrieval and execution of instructions stored in a memory resource 302 (e.g., in a non-transitory computer readable medium). In some examples, the processing resource 312 can be

communicatively coupled to the memory resource 302 through a communication channel 336. In some examples, the communication channel 336 can be a physical or wireless connection to allow the processing resource 312 to retrieve and/or execute the instructions stored on the memory resource 302.

[0037] The memory resource 302 may store instructions 338 which may be executed by the processing resource 312 to cause the imaging device 320 to determine a set point temperature for a current print job. As described herein, the set point temperature can be a temperature of the drying zone 322 and/or heated pressure roller 324 to dry or remove distorted properties from partially dried inkjet media of the current print job. In some examples, a plurality of print jobs can have different set point temperatures based on a number of features of the print job. For example, the set point temperature can be based on, but not limited to, a quantity of print substance deposited on the print media, a surface area of the print media covered by the print substance, a type of print media, a quality of the print job, among other features of the print job.

[0038] The memory resource 302 may store instructions 340 which may be executed by the processing resource 312 to cause the imaging device 320 to determine if a previous print job to the current print job utilized the set point temperature in some examples, the previous print job can be a print job that was performed immediately prior to the print job. As described herein, the previous print job can provide residual heat within the drying zone and/or heated pressure roller, which can allow the drying zone and/or heated pressure roller to be above a threshold temperature.

[0039] In some examples, the set point temperature of the previous print job can be compared to a current print job set point temperature to determine if they are the same value. For example, the previous print job and the current print job can deposit a similar quantity of print substance on a similar area of the print media or have similar print modes. In this example, the temperature set point for the previous print job can be the same or similar to the current print job.

[0040] The memory resource 302 may store instructions 342 which may be executed by the processing resource 312 to cause the imaging device 320 to calculate a seeding pulse width modulation (PWM) value for a proportional- integral-derivative (PID) mode of the heated pressure roller based on a linear interpolation between the set point temperature and a threshold temperature. As described herein, the seeding PWM value for the RID mode can be calculated utilizing an expression such as Expression 1.

[0041] The memory resource 302 may store instructions 344 which may be executed by the processing resource 312 to cause the imaging device 320 to compare a quantity of the seeding PWM value to a quantity of a previous PWM value of the previous print job to determine a higher quantity PWM value. In some examples, the seeding PWM value can be compared to the PWM value of the previous print job. In some examples, the seeding PWM value and the previous PWM value can be quantified by a numerical value (e.g., 47, 41 , etc.) in some examples, the numerical value of the seeding PWM value can be compared to the numerical value of the previous PWM value.

[0042] The memory resource 302 may store instructions 348 which may be executed by the processing resource 312 to cause the imaging device 320 to select the higher quantity PWM value between the seeding PWM value and the previous PWM value. As described herein, the seeding PWM value and the previous PWM value can be represented by numerical values. When the values are compared, the larger numerical value can be selected. For example, the previous PWM value can be selected when the previous PWM value is greater than the seeding PWM value. In another example, the seeding PWM value can be selected when the seeding PV /M value is greater than the previous PWM value.

[0043] The memory resource 302 may store instructions 348 which may be executed by the processing resource 312 to cause the imaging device 320 to apply the selected higher quantity PWM value to alter a temperature of the heated pressure roller from the current temperature to the set point

temperature. As described herein, the selected PWM value can be applied to a PWM controller, which can provide electrical power to a heat source of the drying zone and/or heated pressure roller based on the applied PWM value. In some examples, the rate of temperature increase can correspond to a quantity of the numerical value that represents the PWM value. For example, a relatively larger PWM value can correspond to a relatively higher quantity of heat applied by the beat source, which can increase the temperature at a relatively higher rate compared to a relatively lower PW!VS value.

[0044] Figure 4 illustrates a graph 450 for pulse width modulation value calculations according to an example. Figure 4 illustrates a graph 450 that represents a temperature 454 over a period of time 452 for a drying zone and/or heated pressure roller of an imaging device. As described herein, a print job can include a corresponding set point temperature 458 and a threshold temperature 456 As described herein, the threshold temperature 456 can be a temperature value that corresponds to a temperature when the imaging device either starts from a ramp mode or a RID mode. Thus, in some examples, the threshold temperature 456 can be referred to as a direct RID threshold value.

[0045] As used herein, a print job sequence can include temperature values over a period of time from a starf time of a print job or print jobs to an end time of a print job or print jobs. In some examples, a current print job can be affected by a previous print job. For example, the previous print job could be utilizing the drying zone and/or heated pressure roller and the temperature of the drying zone and/or heated pressure roller can be above the threshold temperature 456 when the imaging device receives the print job or initiates the print job. Figure 4 illustrates a temperature 454 over a period of time 452 for a previous print job sequence 460.

[0048] Figure 4 illustrates an example first print job sequence

represented by a dashed line and an example second print job sequence represented by a solid line. As Illustrated in Figure 4, the temperatures of the drying zone and/or heated pressure roller corresponding to print job sequences begin to drop or cool down after the previous print jobs in the sequences 460. This can be due to the imaging device deactivating the heat source

corresponding to the drying zone and/or heated pressure roller at the completion of the previous print jobs in the sequences 460.

[0047] The dashed line print job sequence has a starting temperature 462 that can be positioned above the threshold temperature 456 and below the set point temperature 458. As described herein, a seeding PWM value can be calculated for the dashed line print job sequence when it is determined that the dashed line print job sequence starting temperature 462 is above the threshold temperature 456. Figure 4 illustrates Expression 1 being utilized to calculate a seeding value for the dashed line print job sequence at 466. In the example for the dashed line print job sequence illustrated in Figure 4, the previous PWM value (PWMp_rev) tor the prior print job in the sequence is 47, the maximum PWM value (PWM max) is 64, the temperature set point (T_set) is 1 10, the starting temperature (T_star_t) is 104 degrees Celsius, and the threshold temperature (PI D_thres_hoi ) is 85 degrees Celsius. As illustrated by the expression at 466, the seeding value for the start in the dashed line print job sequence is calculated to be 51.

[0048] The solid line print job sequence starting temperature 464 can be positioned above the threshold temperature 456 and below the set point temperature 458. As described herein, a seeding PWM value can be calculated for the solid line print job sequence when it is determined that the solid line print job sequence starting temperature 464 is above the threshold temperature 456. Figure 4 also illustrates Expression 1 being utilized to calculate a seeding value for the solid line print job sequence at 468. in this example for the solid line print job sequence and previous print job 460 of the solid line print job sequence illustrated in Figure 4, the previous PWM value (PWMprev) for the solid line print job sequence is 40, the maximum PWM value (PWM max) is 64, the temperature set point (T_sei) is 1 10, the starting temperature (Ts_tar_t) is 88 degrees Celsius, and the threshold temperature (PI D_thres_hoid) is 85 degrees Celsius. As illustrated by the expression at 468, the seeding value for the solid line print job sequence is calculated to be 61.

[0049] Figure 5 is a process 570 for pulse width modulation value calculations according to an example. The process 570 as illustrated in Figure 5 can be a method that can be executed by a computing device, controller, and/or other type of device associated with an imaging device. For example, the process 570 can be stored as instructions in a non-transitory machine readable medium and executed by a processor to perform the elements of the process 570. [0050] Figure 5 illustrates a current print job start at 572. As described herein, the starting time for a print job can be when an imaging device begins to process to the print job. That is, the print job start at 572 can represent a time when the imaging device initiates the print process to generate an image on the print media. At this time, the imaging device can begin to determine current temperatures of the drying zone and/or heated pressure roller.

[0051] At 574, the process 570 can include determining if the current temperature of the drying zone and/or heated pressure roller is greater than temperature set point minus 25 degrees. As described herein, a first threshold temperature to not start in a ramp up mode and to start in a RID mode can be calculated using the set point temperature for the print job minus 25 degrees. Thus, at 574, the process 570 can include determining whether a current temperature of the drying zone and/or heated pressure roller is above a first threshold temperature.

[0052] At 592, the process 570 can apply a full or maximum PWM value when the answer to 574 is no. That is, the process 570 can move to 592 when the current temperature of the drying zone and/or heated pressure roller is less than the first threshold temperature. As described herein, the imaging device can be in a ramp up mode, which can utilize the maximum PW!V! value, to increase the temperature up to a second threshold temperature before switching to a PID mode. At 594, the process 570 can determine if the temperature of the drying zone and/or heated pressure roller is above the second threshold temperature. In some examples, the second threshold temperature can be the set point temperature minus five degrees. In some examples, the second threshold temperature can be utilized instead of the first threshold temperature when the start temperature is below the first threshold and the imaging device starts a print job in a ramp mode. Once the temperature is above the second threshold temperature, the process 570 can move to 598. At 596, the process 570 can switch from the ramp mode to the P!D mode. The process 570 can then move to 590 and perform a regular PID control to maintain the temperature at a set point temperature. In some examples, the process 570 can utilize a RID control loop to maintain the temperature at the set point temperature.

[0053] In some examples, the process 570 can determine at 574 that the current temperature of the drying zone and/or heated pressure roller is above the first threshold temperature in these examples, the process 570 can move to 578 to retrieve a minimum PWM value for the imaging device. As described herein, the minimum PWM value can be set by a PWM controller. In this example, the process 570 can move to 586 to calculate a seeding PWM value. As described herein, the seeding PWM value can be calculated utilizing

Expression 1. However, at 586, the seeding PWM value can be calculated using Expression 1 and replacing the previous PWM value with a minimum PWM value (PWMmin). Thus, at 586, Expression 2 can be utilized.

PWMseed - (PW min + (PWMmax - PWMmin)) X ((T set - Tstart) / (Tset— PIDthreshold))

Expression 2

[0054] In some examples, the process 570 can also move to 576. At 576, the process can determine if the previous print job has the same set point temperature as a current print job. If the set point temperature is different, then the process 570 can move to 582 and set the previous PWM value at 0. If the set point temperature for the current print job is the same as the previous print job, the process 570 can move to 580 to determine if there is an ending PWM value from a previous print job. If there is not an ending PWM value from the previous print job that is saved or stored, the process 570 can move to 582. If there is an ending PWM value from the previous print job that is saved or stored, the process can move to 584 to retrieve the previous PWM value for the previous print job.

[0055] At 588, the process 570 can compare the seeding PWM value calculated at 586 to the previous PWM value retrieved at 584. In addition, at 588, the process 570 can select the greater PWM value between the seeding PWM value and the previous PWM value in some examples, the process 570 can select the previous PWM value when the current temperature is within a particular threshold temperature of the set point temperature. That is, when the current temperature is relatively close to the set point temperature, and the previous set point temperature was the same, the process 570 can simply select the previous PWM value to maintain the set point temperature. In some examples, the process 570 can apply the greater PWM value and move to 590 to move the temperature towards the setpoint and then maintain the

temperature at the set point temperature.

[0056] In the foregoing detailed description of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration how examples of the disclosure can be practiced. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the examples of this disclosure, and it is to be understood that other examples can be utilized and that process, electrical, and/or structural changes can be made without departing from the scope of the disclosure.

[0057] The figures herein follow a numbering convention in which the first digit corresponds to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures can be identified by the use of similar digits. For example, 221 can reference element“21” in Figure 2, and a similar element can be referenced as 321 in Figure 3. Elements shown in the various figures herein can be added, exchanged, and/or eliminated so as to provide a plurality of additional examples of the disclosure. In addition, the proportion and the relative scale of the elements provided in the figures are intended to illustrate the examples of the disclosure and should not be taken in a limiting sense.

Claims

Wtiat is claimed:

1. A non-transitory machine readable medium storing instructions executable by a processing resource to:

determine that a start temperature of a heated pressure roller is above a threshold temperature;

calculate a pulse width modulation (PWM) value for the heated pressure roller based on a set point for the heated pressure roller and a difference between the start temperature and the threshold temperature; and

apply the calculated PWM value as a seeding value for the heated pressure roller in response to a determination that the start temperature is above the threshold temperature.

2. The medium of claim 1 , wherein the threshold temperature is a temperature that when exceeded initiates a proportional integral derivative mode for the heated pressure roller.

3. The medium of claim 1 , wherein the calculated PWM value is proportional to a difference between the set point temperature and the start temperature for the heated pressure roller.

4. The medium of claim 1 , comprising instructions executable by the processing resource to retrieve a minimum PWM value for the heated pressure roller when a previous PWM vaiue is not avaiiabie.

5. The medium of claim 4 wherein the minimum PWM vaiue is calculated based on a voltage applied to a heat source of the heated pressure roller.

6. The medium of claim 1 , wherein the PWM value is applied to maintain a temperature of the heated pressure roller above the threshold temperature of the set point for the heated pressure roller.

7. The medium of claim 1 , wherein the calculated PWM value is additionally based on a maximum PWM value for the heated pressure roller.

8. A controller for a drying zone, comprising:

a processing resource to:

determine that a current temperature of the drying zone of an imaging device is above a threshold temperature of a set point temperature for the drying zone;

calculate a seeding pulse width modulation (PWM) value for a proportional-integral-derivative (PID) mode of the controller for the drying zone based on a linear interpolation between the set point temperature and the threshold temperature; and

apply the seeding PWM value to alter a temperature of the drying zone from the current temperature to the set point temperature.

9. The controller of claim 8, wherein the seeding PWM value is further based on a previous PWM value for a previous print job of the imaging device.

10. The controller of claim 8, wherein the seeding PWM value is between a minimum PWM value and a maximum PWM value for the PID mode of the controller.

11. The controller of claim 10, wherein the maximum PWM value for the P!D mode of the controller is a ramp mode PWM value and the minimum PWM value for the PID mode of the controller is a maintenance mode.

12. The controller of claim 10, wherein the processing resource is to start the controller in the PID mode rather than a ramp mode in response to a determination that the current temperature of the drying zone exceeds the threshold temperature of the set point temperature for the drying zone.

13 An imaging device, comprising: a drying zone that includes a heated pressure roller, wherein the heated pressure roller includes a heat source to increase a temperature of the heated pressure roller; and

a non-transitory computer readable medium storing instructions executable by a processing resource to:

determine a set point temperature for a current print job;

determine if a previous print job to the current print job utilized the set point temperature;

calculate a seeding pulse width modulation (PWM) value for a proportional-integral-derivative (RID) mode of the heated pressure roller based on a linear interpolation between the set point temperature and a threshold temperature;

compare a quantity of the seeding PWM value to a quantity of a previous PWM value of the previous print job to determine a higher quantity PWM value;

select the higher quantity PWM value between the seeding PWM value and the previous PWM value; and

apply the selected higher quantity PWM value to alter a temperature of the heated pressure roller from the current temperature to the set point temperature.

14. The imaging device of claim 13, comprising instructions executable by the processing resource to utilize the applied PWM value as a starting value for a PWM controller.

15. The imaging device of claim 13, comprising instructions executable by the processing resource to:

determine that a previous PWM value for the previous print job does not exist; and

assign a value of zero to the previous PWM value for the previous print job.