English:
[0001] In some printing applications, dryers are employed to speed up the overall printing process. This can be implemented by supplying heat to rapidly dry dispensed ink on a given substrate, such as paper or other media. For example, some printing applications may utilize higher power dryers to dry the ink after it is dispensed. Since the dryers can operate at higher power, safety systems can be provided to help ensure that the dryer is operating within expected operating parameters.
[0002] FIG. 1 is a block diagram illustrating an example of a circuit to monitor a fan rotation signal.
[0003] FIG. 2 is a block diagram illustrating an example of a circuit to monitor a fan rotation signal and temperature.
[0004] FIG. 3 is a circuit diagram illustrating an example of a circuit to monitor a fan rotation signal.
[0005] FIG. 4 is an example circuit diagram illustrating a temperature circuit to monitor temperature and to generate a temperature control signal for a printer dryer.
[0006] FIG. 5 is a circuit diagram illustrating an example of a gating circuit to generate a combined control signal to control a printer dryer.
[0007] FIG. 6 is a flow diagram illustrating an example method to monitor a fan rotation signal.
[0008] This disclosure relates to a circuit that monitors fan speed signals and/or temperature signals of a printer with respect to one or more predetermined thresholds and to control a printer dryer based on satisfying the threshold(s). In one example, a circuit includes a pulse generator to generate an output pulse in response to a signal representing rotation of a fan. This rotation signal can be a received from an encoder coupled to the shaft of the fan, for example. A timing relationship between output pulses represents speed of the fan. In one example, the output pulse can have a duty cycle having a fixed on time parameter where the off time parameter of the output pulse varies according to the speed of the fan. A filter circuit (e.g., resistor/capacitor (RC) filter) converts the output pulse to a direct current (DC) voltage signal proportional to the speed of the fan. A monitor circuit monitors the DC voltage signal with respect to a predetermined threshold and generates a control signal that disables a printer dryer if the DC signal does not satisfy the predetermined threshold. A temperature circuit can also be provided to monitor temperature (e.g., within the printer housing) with respect to a predetermined threshold and to generate a temperature control signal if the temperature satisfies the predetermined threshold. The fan speed control signal and the temperature control signal can be gated to generate a combined control signal to disable the dryer if each of the predetermined thresholds is not satisfied. Thus, if either of the thresholds is not satisfied, however, the circuit can employ a safety interlock to shut down the dryer in the absence of processor intervention.
[0009] By monitoring fan speed and/or temperature as a stand-alone circuit outside of processor interaction, various improvements can be achieved over conventional dryer control schemes. Conventional circuits utilize expensive frequency to voltage converter integrated circuits that had to have their outputs digitized, read by an analog to digital converter (ADC), and processed by a processor to determine fan speed. The circuits in this disclosure provide pulse generation and filtering techniques that mitigate the need for expensive frequency conversion and ADC circuits. Moreover, the circuits disclosed herein provide an additional layer of redundancy for failure detection. If a processor were to fail in conventional circuits, printer fan speeds and/or dryer temperatures could remain unchecked and uncontrolled due to the processor failure. The stand-alone circuits described herein can monitor fan speed/temperature and disable the dryer outside of processor interaction. This provides additional monitoring and control of the dryer over conventional circuits regardless of the state of the processor.
[0010] FIG. 1 illustrates an example block diagram of a circuit 100 to monitor a fan rotation signal 1 10 and to generate a control signal 120 to a printer dryer based on the rotation signal. As used herein, the term circuit can include a collection of active and/or passive elements that perform a circuit function, such as an analog circuit, digital circuit or a combination thereof, such as to provide a control circuit, for example. Additionally or alternatively, the term circuit can include an integrated circuit where all and/or some of the circuit elements are fabricated on a common substrate, for example.
[0011] As shown in the example of FIG. 1 , the circuit 100 includes a pulse generator 130 to generate an output pulse 134 in response to the signal 1 10 representing rotation of a fan (not shown). A timing relationship between output pulses 134 represents speed of the fan. A filter circuit 140 converts the output pulse 134 to a direct current (DC) voltage signal 144 proportional to the speed of the fan. A monitor circuit 150 monitors the DC voltage signal 144 with respect to a predetermined threshold and generates the control signal 120 that disables a printer dryer (not shown) if the DC signal does not satisfy the predetermined threshold.
[0012] As an example, a one-kilowatt (kW) power dryer (or other power range) can be provided with the respective printer, which includes the use of interlock circuitry, such as described herein, to mitigate unsafe operation. These circuits provide a low- cost, standalone solution for monitoring both fan speed and temperature and preventing energizing of the heating elements of the dryer should either or both of these inputs be outside of a predetermined range. Due to the circuit's ability to operate standalone, it can provide a backup in the event that a firmware failure should occur. Prior solutions included dedicated frequency to voltage conversion circuits for determination of fan speed. However, this solution has the disadvantage of being significantly more expensive. Other solutions involved the use of firmware to monitor both fan speed and temperature directly. However, this has the disadvantage of a single point of failure being able to cause a safety concern.
[0013] The circuit 100 provides a safety interlock function for the dryer by monitoring fan speed as well as dryer temperature and preventing firmware from energizing heating element(s) if either input is outside of a predetermined range. The circuit 100 operates standalone therefore allowing it to function as a redundant backup to firmware controlled interlocks. Outputs from the circuit fan and temperature circuits described herein enable firmware to monitor the state of the interlock and determine if either or both inputs are determined to be out of range.
[0014] The signal 144 representing rotation speed of the fan can be an encoder signal representing rotation of the fan, for example, however other types of devices are possible such as a resolver that is coupled to the shaft of the fan. The output pulse 134 can have a duty cycle that represents the speed of the fan. For instance, the output pulse 134 can have a fixed on time parameter that is triggered via a rising or falling edge of the signal 1 10 representing rotation of the fan and a variable off time parameter that varies with the speed of the fan. In other example implementations, the off time parameter could be fixed and the on time parameter varied with the speed of the fan.
[0015] Temperature in the printer dryer can be controlled by enabling/disabling triacs to apply alternating current (AC) to or remove AC from the heating elements in the dryer which can in turn be controlled by the control signals described herein (see e.g., control signals at D29 pins 1 and 2 of FIG. 5). The logic/control signals that perform these functions can be gated (e.g., only enabled to be passed to the triacs in the event the fan speed is above a minimum threshold level and the dryer temperature within a valid temperature range). Print media (e.g., paper) in the printer can be physically separated from the heating elements in the dryer and the fan is utilized to blow heated air across the page to be printed as it passes through a given portion of the paper path. Fan speed can be determined based upon density of the print and may not be used to regulate temperature in the dryer. In other example applications, fan speed can be utilized to regulate temperature of the dryer. However, having a minimum fan speed provides several advantages. The fan speed enables airflow across a thermistor (or other temperature sensor) to ensure accurate readings are being made of the temperature in the dryer. Also, the fan speed serves to mitigate degradation of the thermal fuses in the dryer due to normal operation that could lead to early life failures. Such fuses can be provided to open in the event of a failure, (e.g., powering of the heating elements without the fan running).
[0016] As disclosed herein, such as with respect to FIG. 3, the pulse generator 130 can include a comparator to compare the signal 1 10 representing rotation of the fan with a predetermined signal threshold and to generate an output based on the comparison. The output from the comparator can trigger a monostable circuit, for example, to generate a single pulse having a fixed on time and a variable off time representing the speed of the fan. The filter circuit 140 can be any type of filter to convert the output pulse 134 into a DC value. In one specific example, a resistor/capacitor (RC) filter can be employed in the filter circuit 140.
[0017] The monitor circuit 150 can also include a comparator to monitor the DC voltage signal 144 proportional to fan speed with respect to the predetermined threshold. In addition to fan speed monitoring, temperature monitoring can also be provided such as illustrated in FIGS. 2 and 4 described below. This can include a temperature circuit to monitor temperature with respect to a predetermined threshold and to generate a temperature control signal if the temperature satisfies the predetermined threshold. The fan speed control signal and the temperature control signal can be gated to generate a combined control signal to disable the dryer if the predetermined thresholds are not satisfied. Additionally, a DC monitor circuit (see e.g., FIG. 5) can be provided to disable the combined control signal if a power supply input rail to the comparator does not satisfy a predetermined supply threshold.
[0019] The circuit 200 includes a temperature circuit 260 to monitor temperature from a sensor signal 264 with respect to a predetermined temperature threshold and generates a temperature control signal 270 if the temperature satisfies the predetermined threshold. The fan control signal 254 and the temperature control signal 270 can be supplied in tandem to a gating circuit shown at reference numeral 274 and can be gated (e.g., via a logic gate) to generate a combined control signal to disable the dryer if each of the predetermined thresholds is not satisfied. The gating circuitry is depicted in FIG. 5 where the signal 254 is routed to pin 1 of gate D29 and signal 270 is routed to pin 2 of gate D29 of FIG. 5. The temperature circuit 260 can include a window comparator that monitors for both a maximum and minimum temperature for operation of the printer dryer. If the sensor signal 264 (e.g., thermistor signal) is below a predetermined low temperature threshold or above a predetermined high temperature threshold set by the window comparator, the temperature control signal 270 can be set to disable the dryer, for example, via temperature control signal 270. An example circuit implementation for the circuit of FIG. 1 is shown in FIG. 3. An example circuit implementation for the temperature circuit 260 is shown in FIG. 4. An example circuit implementation for the gating circuit described herein is shown in FIG. 5.
[0020] FIG. 3 illustrates an example of a circuit 300 to monitor a fan rotation signal and to generate a control signal to a printer dryer based on the rotation signal. The fan rotation signal is received at an input (IN) of a pulse generator 310 which drives a filter circuit 320 which is in turn monitored by monitor circuit 330 to generate a control output signal shown as (OUT). The circuit 300 includes the pulse generator 310 to convert the fan rotation signal to a series of pulses, which is then filtered to a DC value via the filter circuit 320 and compared to a reference voltage via U37 pin 2 corresponding to a revolutions per minute (RPM) level above which the dryer is allowed to operate. A dual comparator integrated circuit U37 can be utilized to perform both functions of pulse generation and monitoring as described herein.
[0021] The fan rotation signal at IN can be coupled via capacitor 1061 and received via pin 5 of U37 to provide sufficiently fast edges and this signal AC coupled to the non- inverting input of the comparator U37. In some examples, buffering may be provided to the fan signal before it is received at the input IN. A reference threshold is set via R945 and R946 (e.g., magnitude of the falling edge of the fan rotation signal) where diodes of integrated circuit D28 provide input clamping to a minimum negative threshold for U37. The output of the comparator U37 pin 7 is inverted by the common-source amplifier formed by M1 and R964 and fed back to the inverting input pin 6 of U37 through an RC network comprised of C1062 and R948. The transistor M1 is driven via RC network of resistors R964, R965, R966, and capacitor C1074. Output duty cycle pulse control is provided via C1062 and R948. R964 provides a pull-up for the open drain output of U37. The resistors R945 and R946 can be sized such that their Thevenin equivalent resistance is approximately that of R948 to mitigate the impact of input bias current.
[0022] The output from pin 3 of M1 , which functions as a common source amplifier in monostable multivibrator (e.g., the pulse generator circuit depicted in 310), is a pulse with fixed on time and varying duty cycle. On time can be set using the RC network referenced above and duty cycle is proportional to frequency of the fan rotation signal (e.g., each falling edge of encoder output). One fixed on time pulse can be generated on each falling edge of the fan rotation signal (e.g., each falling edge of encoder output). This pulse-width modulated (PWM) signal at pin 3 of M1 can then be filtered via filter circuit 320 to provide an analog voltage with minimal ripple. At this point, the signal could be fed into an ADC to be measured but in order for the circuit to operate standalone, it is instead fed into the non-inverting input pin 3 of dual comparator U37.
[0023] The filter circuit can include R949 and R1067 which form filters with C1063 and C1 151 , respectively. Output from the filter 320 is fed though R950 to non-inverting input pin 3 of U37. The inverting input can be set to a threshold voltage via R951 and R952 corresponding to the threshold above which dryer operation is allowed. Capacitor C1065 provides filtering action for the non-inverting input pin 2 of U37 and resistor R953 provides feedback for the comparator. Resistor R954 and C1067 provide output filtering for the signal OUT from the comparator U37. The output signal OUT of the comparator U37 can be a logic high when the voltage corresponding to the fan speed crosses above this threshold value set by R951 and R952. Hysteresis can be provided via R953 to prevent the output of the comparator U37 from switching multiple times as the signal crosses through this threshold level. This output signal OUT can be routed to a digital input pin to provide feedback regarding the state of the hardware.
[0024] FIG. 4 is an example of a temperature circuit 400 to monitor temperature and to generate a temperature control signal 410 to a printer dryer based on the temperature. In this example, a window comparator formed from dual comparator U34 is utilized to provide indication of the dryer temperature being within a valid range. The output of a biased thermistor is received by input (IN), with threshold values set corresponding to the minimum and maximum temperatures for which operation of the dryer is allowed. The maximum threshold can be set by resistors R787 and R786 with some filtering provided by C875. The minimum temperature threshold can be set by resistors R866 and R867 with some filtering provided by C877. Resistors R789 and R790 provide hysteresis feedback for the respective comparators of U34. The input IN is fed to the comparators via resistor R862 and R860.
[0025] Setting the threshold values to correspond to values outside of the allowed temperature range of the dryer also allows the circuit to be used to detect significant sensor issues, such as a shorted or opened (e.g. uninstalled) thermistor. Output of the window comparator shown as OUT can be a logic high when the temperature is within a valid range. Hysteresis can be provided to prevent the output of the comparators from switching multiple times as the input signal crosses through either threshold level. This output signal OUT can be routed to a digital input pin to provide feedback regarding the state of this hardware. Additional output filtering can be provided by capacitor C1068 and R787 provides a pull-up for U34.
[0026] FIG. 5 is an example of a gating circuit 500 to generate a combined control signal to control a printer dryer from the fan control signal and the temperature control signal of FIG. 2. The output signals from the fan monitoring and temperature circuits described herein can be logically AND'ed together via gate D29 to generate a combined control signal at pin 3 of D29. This signal is then logically AND'ed with any number of active high enable signals used for energizing heating elements in the dryer. In this example, two control gates U38 and U39 are provided which receive firmware signals via inputs marked as (IN). The inputs may be pulled down via resistors R608 and R957. Output from gate D29 may be filtered via C1069 and R956 acts as a pull-up. The combined control signal from D29 pin 3 can be gated with firmware control signals received at inputs IN via gates U34 to provide dryer control signals shown at (OUT). This can prevent firmware control of heating elements until all inputs are within a valid range and can prevent situations where a firmware failure could cause a safety concern. The outputs of U38 can be filtered via resistor R958 and capacitor C1071 . The outputs of the driver U39 can be filtered via resistor R959 and capacitor C1072.
[0027] An additional safety circuit can be provided to monitor for the presence of a voltage rail - in this example the rail identified as V1 (e.g., 5.1 volts), which supplies the comparators U34 and U37. Dual transistor U75 can be employed to provide such monitoring. Input voltage for V1 (e.g., 5.1 volts) is monitored with respect to a predetermined voltage supply threshold via pin 5 of Q75 via bias resistors R967 and R968, where capacitor C1 143 provides filtering. Q75 receives V2 at its emitter and drives resistors R1057 and 1058 along with capacitor C1 142 at its collector. Another transistor of Q75 can disable the output of D29 by pulling its output to ground if the V1 rail in this example is lost. This circuit provides an additional interlock for the fan and temperature control signals gated by D29.
[0028] In view of the foregoing structural and functional features described above, an example method will be better appreciated with reference to FIG. 6. While, for purposes of simplicity of explanation, the method is shown and described as executing serially, the method is not limited by the illustrated order, as parts of the method could occur in different orders and/or concurrently from that shown and described herein. Such methods can be executed by various components configured in one or more integrated circuits, a processor, or a controller, for example.
[0029] FIG. 6 illustrates an example method 600 to monitor a fan rotation signal and to generate a control signal to a printer dryer based on the rotation signal. At 610, the method 600 includes generating an output pulse in response to a signal representing rotation of a fan (e.g., via pulse generator 130 of FIG. 1 ). A timing relationship between output pulses represents speed of the fan. At 620, the method 600 includes converting the output pulse to a direct current (DC) voltage signal proportional to the speed of the fan (e.g., via filter circuit 140 of FIG. 1 ). At 630, the method 600 includes monitoring the DC voltage signal with respect to a predetermined threshold (e.g., via monitor circuit 150 of FIG. 1 ). At 640, the method 600 includes generating a control signal that disables a printer dryer if the DC signal does not satisfy the predetermined threshold (e.g., via monitor circuit 150 of FIG. 1 ). The method 600 can also include generating the output pulse in response to a rising or falling edge of the signal representing rotation of the fan, the output pulse having a fixed on-time parameter and a variable off-time parameter that varies with the speed of the fan.

中文:
[0001]在一些打印应用中,采用干燥器来加速整个打印过程。这可以通过供应热量以快速地使所分配的油墨在诸如纸张或其他介质等给定基底上干燥来实现。例如,一些打印应用可以利用较高功率的干燥器来在油墨被分配之后使其干燥。由于干燥器可以以较高的功率进行操作,因此可以提供安全系统以帮助确保干燥器在预期的操作参数内进行操作。
[0002]图1是示出对风扇旋转信号进行监测的电路的示例的框图。
[0003]图2是示出对风扇旋转信号和温度进行监测的电路的示例的框图。
[0004]图3是示出对风扇旋转信号进行监测的电路的示例的电路图。
[0005]图4是示出对温度进行监测并且生成用于打印机干燥器的温度控制信号的温度电路的示例电路图。
[0006]图5是示出生成组合控制信号以对打印机干燥器进行控制的选通电路的示例的电路图。
[0007]图6是示出对风扇旋转信号进行监测的示例方法的流程图。
[0008]本公开涉及一种电路,该电路相对于一个或多个预定阈值而对打印机的风扇速度信号和/或温度信号进行监测并且基于满足阈值来对打印机干燥器进行控制。在一个示例中,一种电路包括:脉冲发生器,用于响应于表示风扇旋转的信号而生成输出脉冲。该旋转信号可以例如从被耦接到风扇的轴的编码器接收。输出脉冲之间的时序关系表示风扇速度。在一个示例中,输出脉冲可以具有:具有固定导通时间参数的占空比,其中输出脉冲的截止时间参数根据风扇速度而变化。滤波器电路(例如,电阻器/电容器(RC)滤波器)将输出脉冲转换为与风扇速度成比例的直流(DC)电压信号。监测器电路相对于预定阈值而对DC电压信号进行监测,并且如果DC信号不满足预定阈值,则生成禁用打印机干燥器的控制信号。还可以提供温度电路以相对于预定阈值而对温度(例如,在打印机壳体内)进行监测并且如果温度满足预定阈值则生成温度控制信号。如果不满足预定阈值中的每个,则风扇速度控制信号和温度控制信号可以被选通以生成组合控制信号,以禁用干燥器。因此,如果不满足任何一个阈值,则在没有处理器干预的情况下,电路可以采用安全互锁来关闭干燥器。
[0009]通过将风扇速度和/或温度作为处理器交互之外的独立电路来进行监测,可以在传统干燥器控制方案上实现各种改进。传统电路利用昂贵的频率至电压转换器集成电路,该频率至电压转换器集成电路必须将其输出数字化,并由模数转换器(ADC)读取,并且由处理器处理以确定风扇速度。本公开中的电路提供脉冲生成和滤波技术,该技术减少了对昂贵的频率转换和ADC电路的需求。此外,本文所公开的电路为故障检测提供了额外的冗余层。如果处理器在传统电路中出现故障,则打印机风扇速度和/或干燥器温度可能会由于处理器故障而保持不被检测和不受控制。本文所描述的独立电路可以对风扇速度/温度进行监测并且在处理器交互之外禁用干燥器。无论处理器的状态如何,这都在传统电路上提供了额外的干燥器监测及控制。
[0010]图1示出电路100的示例框图,该电路100用于对风扇旋转信号110进行监测并且基于该旋转信号来生成至打印机干燥器的控制信号120。如本文所使用的,术语电路例如可以包括执行电路功能的有源和/或无源元件的集合,诸如模拟电路、数字电路或它们的组合等,诸如用于提供控制电路。附加地或可替代地,术语电路例如可以包括集成电路,其中所有和/或一些电路元件被制造于公共基底上。
[0011]如图1的示例所示,电路100包括脉冲发生器130,该脉冲发生器130响应于表示风扇(未示出)旋转的信号110而生成输出脉冲134。输出脉冲134之间的时序关系表示风扇速度。滤波器电路140将输出脉冲134转换为与风扇速度成比例的直流(DC)电压信号144。监测器电路150相对于预定阈值而对DC电压信号144进行监测,并且如果DC信号不满足预定阈值,则生成禁用打印机干燥器(未示出)的控制信号120。
[0012]作为示例,可以为相应的打印机提供一千瓦(kW)功率(或其他功率范围)干燥器,其包括使用诸如本文所描述的互锁电路以减轻不安全操作。这些电路提供了一种低成本的独立解决方案,该方案用于对风扇速度和温度进行监测并且如果这些输入中的任何一个或两个都在预定范围之外则防止干燥器的加热元件通电。由于电路的独立运行能力,因此它可以在发生固件故障时提供备份。先前的解决方案包括用于确定风扇速度的专用频率至电压转换电路。然而,该解决方案具有明显更昂贵的缺点。其他解决方案涉及使用固件来直接对风扇速度和温度进行监测。然而,这具有单点故障可能会引发安全问题的缺点。
[0013]电路100通过对风扇速度以及干燥器温度进行监测来为干燥器提供安全互锁功能,并且如果任一输入在预定范围之外,则防止固件给加热元件通电。电路100独立进行操作,因此允许其作为固件控制互锁的冗余备份来发挥作用。来自本文所描述的电路风扇和温度电路的输出使固件能够对互锁状态进行监测并且确定其中一个或两个输入是否被确定为超出范围。
[0014]表示风扇转速的信号144例如可以是表示风扇旋转的编码器信号,然而其他类型的设备也是可行的,诸如耦接到风扇的轴的旋转变压器。输出脉冲134可以具有表示风扇速度的占空比。例如,输出脉冲134可以具有通过表示风扇旋转的信号110的上升沿或下降沿而被触发的固定导通时间参数、以及随风扇速度变化的可变截止时间参数。在其他示例实现中,截止时间参数可以是固定的,并且导通时间参数随着风扇速度而变化。
[0015]可以通过启用/禁用三端双向可控硅开关来对打印机干燥器中的温度进行控制,以对干燥器中的加热元件施加交流电(AC)或者从干燥器中的加热元件去除AC,而干燥器又可以通过本文所描述的控制信号来控制(参见例如图5的D29引脚1和2处的控制信号)。执行这些功能的逻辑/控制信号可以被选通(例如,在风扇速度高于最小阈值水平并且干燥器温度在有效温度范围内的情况下,仅能够传递到三端双向可控硅开关)。打印机中的打印介质(例如纸张)可以与干燥器中的加热元件物理分离,并且风扇被用于在页面通过纸张路径的给定部分时将加热后的空气吹在待打印的页面上。风扇速度可以基于打印密度来确定,并且可以不被用于调节干燥器中的温度。在其他示例应用中,风扇速度可以被用于调节干燥器的温度。然而,具有最小风扇速度提供了若干优点。风扇速度使气流能够穿过热敏电阻(或其他温度传感器),以确保干燥器中的温度的准确读数。而且,风扇速度用于减轻干燥器中的热熔断器的劣化,而这种劣化是由于可能会导致早期寿命故障的正常操作而导致的。可以提供这种熔断器以在发生故障时开路(例如,在没有风扇运转的情况下为加热元件供电)。
[0016]如本文所公开的,诸如关于图3,脉冲发生器130可以包括比较器,该比较器将表示风扇旋转的信号110与预定信号阈值进行比较并且基于该比较来生成输出。来自比较器的输出可以触发单稳态电路,例如,生成具有固定导通时间以及表示风扇速度的可变截止时间的单脉冲。滤波器电路140可以是任何类型的滤波器,用于将输出脉冲134转换为DC值。在一个特定示例中,可以在滤波器电路140中采用电阻器/电容器(RC)滤波器。
[0017]监测器电路150也可以包括比较器,该比较器相对于预定阈值而对与风扇速度成比例的DC电压信号144进行监测。除了风扇速度监测之外,还可以提供温度监测,诸如在下面描述的图2和图4中所示。这可以包括温度电路以相对于预定阈值而对温度进行监测,并且如果该温度满足预定阈值则生成温度控制信号。如果不满足预定阈值,则风扇速度控制信号和温度控制信号可以被选通以生成组合控制信号,用于禁用干燥器。可替代地,如果至比较器的电源输入轨不满足预定电源阈值,则可以提供DC监测器电路(参见例如图5)以禁用组合控制信号。
[0019]电路200包括温度电路260,该温度电路260相对于预定温度阈值而对来自传感器信号264的温度进行监测,并且如果该温度满足预定阈值则生成温度控制信号270。风扇控制信号254和温度控制信号270可以被串联地供应给附图标记274所示的选通电路,并且如果预定阈值中的每个都未被满足则可以被选通(例如,通过逻辑门)以生成组合控制信号,用于禁用干燥器。选通电路如图5所示,其中信号254被路由到门D29的引脚1,并且信号270被路由到图5的门D29的引脚2。温度电路260可以包括窗口比较器,该窗口比较器对用于打印机干燥器的操作的最高和最低温度进行监测。如果传感器信号264(例如,热敏电阻信号)低于由窗口比较器设定的预定低温阈值或者高于由窗口比较器设定的预定高温阈值,则可以设置温度控制信号270,用于例如通过温度控制信号270来禁用干燥器。图3中示出了图1的电路的示例电路实现。图4中示出了温度电路260的示例电路实现。图5中示出了本文所描述的选通电路的示例电路实现。
[0020]图3示出电路300的示例,该电路300用于对风扇旋转信号进行监测并且基于该旋转信号来生成至打印机干燥器的控制信号。在脉冲发生器310的输入端(IN)处接收风扇旋转信号,该脉冲发生器310对滤波器电路320进行驱动,该滤波器电路320又由监测器电路330来监测以生成被示出为(OUT)的控制输出信号。电路300包括脉冲发生器310,该脉冲发生器310用于将风扇旋转信号转换为一系列脉冲,该一系列脉冲然后通过滤波器电路320被滤波为DC值,并且通过U37引脚2来与对应于每分钟转数(RPM)水平的参考电压进行比较,在该RPM水平之上时干燥机被允许操作。双比较器集成电路U37可以被用于执行如本文所描述的脉冲生成以及监测的功能。
[0021]IN处的风扇旋转信号可以通过电容器1061被耦合并且通过U37的引脚5被接收,用于提供足够快的边沿,并且该信号AC耦合至比较器U37的非反相输入端。在一些示例中,可以在风扇信号在输入IN处被接收到之前对该风扇信号提供缓冲。通过R945和R946来设置参考阈值(例如,风扇旋转信号的下降沿的幅度),其中集成电路D28的二极管为U37的最小负阈值提供输入钳位。比较器U37引脚7的输出通过由M1和R964形成的共源放大器被反相,并且通过由C1062和R948组成的RC网络被反馈到U37的反相输入引脚6。晶体管M1通过电阻器R964、R965、R966与电容器C1074的RC网络来驱动。通过C1062和R948来提供输出占空比脉冲控制。R964为U37的开漏输出(open drain output)提供上拉电阻(pull-up)。电阻器R945和R946的尺寸可以被设定为使得它们的戴维南(Thevenin)等效电阻近似为R948的电阻,以减轻输入偏置电流的影响。
[0022]来自用作单稳态多谐振荡器中的公共源极放大器(例如,310中所描绘的脉冲发生器电路)的M1的引脚3的输出是具有固定的导通时间和变化的占空比的脉冲。导通时间可以使用上面提到的RC网络来设置,并且占空比与风扇旋转信号的频率成比例(例如,编码器输出的每个下降沿)。可以在风扇旋转信号的每个下降沿(例如,编码器输出的每个下降沿)上生成一个固定导通时间脉冲。然后,可以通过滤波器电路320来对M1的引脚3处的该脉冲宽度调制(PWM)信号进行滤波,以提供具有最小纹波的模拟电压。此时,信号可以被馈送至待测量的ADC中,但是为了使电路独立地进行操作,它反而被馈送至双比较器U37的非反相输入引脚3中。
[0023]滤波器电路可以包括R949和R1067,它们分别形成具有C1063和C1151的滤波器。来自滤波器320的输出通过R950被馈送到U37的非反相输入引脚3。反相输入可以通过R951和R952被设置为与阈值对应的阈值电压,在该阈值之上时干燥器被允许操作。电容C1065为U37的非反相输入引脚2提供滤波功能,并且电阻R953为比较器提供反馈。电阻R954和C1067为来自比较器U37的信号OUT提供输出滤波。当与风扇速度对应的电压超过由R951和R952设定的该阈值时,比较器U37的输出信号OUT可以是逻辑高。可以通过R953提供滞后,以防止比较器U37的输出在信号超过该阈值电平时多次切换。该输出信号OUT可以被路由到数字输入引脚,以提供有关硬件状态的反馈。
[0024]图4是温度电路400的示例,该温度电路400用于对温度进行监测并且基于该温度来生成至打印机干燥器的温度控制信号410。在该示例中,利用由双比较器U34形成的窗口比较器来提供干燥器温度在有效范围内的指示。偏置热敏电阻的输出由输入端(IN)接收,其中对应于允许干燥器的操作的最小和最大温度来设置阈值。最大阈值可以通过电阻R787和R786利用由C875提供的一些滤波来设置。最低温度阈值可以通过电阻R866和R867利用由C877提供的一些滤波来设置。电阻R789和R790为U34的各个比较器提供滞后反馈。输入IN通过电阻R862和R860被馈送到比较器。
[0025]将阈值设置为对应于干燥器的允许温度范围之外的值还允许使用该电路来检测重要的传感器问题,诸如短路或开路(例如未安装)的热敏电阻。当温度在有效范围内时,被示出为OUT的窗口比较器的输出可以是逻辑高。可以提供滞后以防止比较器的输出在输入信号超过任一阈值电平时多次切换。该输出信号OUT可以被路由到数字输入引脚,以提供有关该硬件的状态的反馈。可以由电容C1068提供额外的输出滤波,并且R787为U34提供上拉电阻。
[0026]图5是选通电路500的示例,该选通电路500用于根据图2的风扇控制信号和温度控制信号来生成组合控制信号以对打印机干燥器进行控制。来自本文所描述的风扇监测和温度电路的输出信号可以通过门D29被逻辑“与”在一起,以在D29的引脚3处生成组合控制信号。然后,该信号与用于将干燥器中的加热元件通电的任何数量的有效高使能信号被逻辑“与”。在该示例中,提供了两个控制门U38和U39,其通过被标记为(IN)的输入端来接收固件信号。输入端可以通过电阻R608和R957被下拉。来自门D29的输出可以通过C1069被滤波,并且R956用作上拉电阻。来自D29引脚3的组合控制信号可以利用在输入IN处接收到的固件控制信号通过门U34被选通,以提供在(OUT)处所示的干燥器控制信号。这可以防止加热元件的固件控制直至所有输入都在有效范围内为止,并且可以防止固件故障可能会引发安全问题的情况。U38的输出可以通过电阻R958和电容C1071被滤波。驱动器U39的输出可以通过电阻R959和电容C1072被滤波。
[0027]可以提供附加的安全电路来监测电压轨的存在,在该示例中该轨被标识为V1(例如,5.1伏),其为比较器U34和U37供电。双晶体管U75可以被用于提供这种监测。通过Q75的引脚5并经由偏置电阻器R967和R968来相对于预定电源阈值而对V1的输入电压(例如,5.1伏特)进行监测,其中电容器C1143提供滤波。Q75在其发射极处接收V2,并在其集电极处对电阻器R1057和1058以及电容器C1142进行驱动。如果本例中的V1轨丢失,则Q75的另一个晶体管可以通过将其输出拉至地来禁用D29的输出。该电路为由D29选通的风扇和温度控制信号提供了额外的互锁。
[0028]鉴于上述结构和功能特征,参考图6将更好地理解示例方法。虽然为了简化说明的目的,该方法被示出并描述为串行执行,但是该方法不受所示顺序的限制,因为该方法的一部分可以以不同的顺序来发生和/或与本文所示出并描述的顺序同时发生。这种方法例如可以由配置在一个或多个集成电路、处理器或控制器中的各种部件来执行。
[0029]图6示出示例方法600,该示例方法600用于对风扇旋转信号进行监测并且基于该旋转信号来生成至打印机干燥器的控制信号。在610处,方法600包括响应于表示风扇旋转的信号而生成输出脉冲(例如,经由图1的脉冲发生器130)。输出脉冲之间的时序关系表示风扇速度。在620处,方法600包括将输出脉冲转换为与风扇速度成比例的直流(DC)电压信号(例如,经由图1的滤波器电路140)。在630处,方法600包括相对于预定阈值而对DC电压信号进行监测(例如,经由图1的监测器电路150)。在640处,方法600包括如果DC信号不满足预定阈值则生成禁用打印机干燥器的控制信号(例如,经由图1的监测器电路150)。方法600还可以包括响应于表示风扇旋转的信号的上升沿或下降沿而生成输出脉冲,该输出脉冲具有固定导通时间参数、以及随风扇速度变化的可变截止时间参数。