Method for detecting the level of a storage tank

Abstract

The present application provides a method for detecting the liquid level of a storage tank. An optical sensor is determined to be used for liquid level detection when the sensing value of the optical sensor on the tank object meets a critical condition. The optical sensor is further determined to be effective for liquid level detection when the sensing value of the optical sensor on the storage tank without printing material and the sensing value of the optical sensor on the storage tank with printing material meet another critical condition. During printing, the injection of printing material into the storage tank is started or stopped when the sensing value of the optical sensor meets the corresponding critical condition. The present application can avoid sensing errors caused by hardware defects and effectively maintain the liquid level of the storage tank at a normal height.

Description

TECHNICAL FIELD

[0001] The present application relates to a detection method, and in particular, to a detection method for a liquid level of a storage tank. BACKGROUND

[0002] In a conventional printer (e.g. a 2D printer or a 3D printer), in order to avoid printing failure or printer malfunction, it is important to detect the liquid level of a storage tank, i.e. to detect the remaining capacity of printing material in the storage tank.

[0003] For example, when the printing material is too little (i.e. the liquid level is too low), the printing material will be exhausted during printing, resulting in interruption of printing; when the printing material is too much (i.e. the liquid level is too high), the printing material will flow back, resulting in malfunction of the printer.

[0004] In order to effectively detect whether the liquid level is higher or lower than a preset height, a float ball liquid level switch can be provided in the storage tank, but the float ball liquid level switch is relatively expensive. Moreover, the float ball liquid level switch is easily damaged and difficult to maintain because it is immersed in the printing material.

[0005] In addition, if a photoelectric liquid level switch is provided, the manufacturing yield must be considered, and how to set the trigger threshold of the photoelectric liquid level switch must also be considered.

[0006] Specifically, when there is a hardware defect in the photoelectric sensor of the photoelectric liquid level switch, the entire photoelectric liquid level switch must be replaced, increasing the installation cost. Moreover, even if the same process is used, there are differences in sensitivity between different photoelectric sensors, and how to set the correct trigger threshold to ensure that the photoelectric sensor can effectively detect the liquid level, i.e. how to effectively detect the two states of having printing material and not having printing material, becomes an important issue.

[0007] Therefore, the existing liquid level detection has the above problems, and a more effective solution is urgently needed. SUMMARY

[0008] The present application provides a detection method for a liquid level of a storage tank, which uses a sensor capable of detecting the liquid level of different types of liquid to perform liquid level detection and liquid level control.

[0009] In one embodiment, a detection method for a liquid level of a storage tank includes:

[0010] Step a) performing a first sensing process on a tank object by an optical sensor to obtain a first sensing value, wherein the light transmittance of the tank object corresponds to the light transmittance of a storage tank;

[0011] Step b) when the first sensing value meets a first threshold condition, determining that the optical sensor is for liquid level detection;

[0012] Step c) performing a second sensing process on the storage tank by the optical sensor for the liquid level detection purpose to obtain a second sensing value for no print material and a third sensing value for print material, and determining that the optical sensor for the liquid level detection purpose is valid for the liquid level detection when the second sensing value meets a second critical condition and the third sensing value meets a third critical condition;

[0013] Step d) performing a third sensing process on the storage tank by the optical sensor valid for the liquid level detection to obtain a fourth sensing value during a printing process; and

[0014] Step e) starting or stopping the injection of print material into the storage tank when the fourth sensing value meets a fourth critical condition, wherein the fourth critical condition is corresponding to the second sensing value or the third sensing value.

[0015] In an embodiment, the first sensing process comprises:

[0016] Step a1) the optical sensor is detachably installed on a detection tool to perform optical sensing towards the tank object;

[0017] Step a2) a measurement device is coupled to the optical sensor; and

[0018] Step a3) obtaining a voltage value of the optical sensor by the measurement device as the first sensing value.

[0019] In an embodiment, the method for detecting the liquid level of the storage tank further comprises:

[0020] Step f) determining that the optical sensor is not valid for the liquid level detection when the first sensing value does not meet the first critical condition.

[0021] In an embodiment, the second sensing value comprises a first empty tank sensing value, and the second critical condition comprises a first empty tank critical condition;

[0022] wherein the step c) comprises:

[0023] Step c11) increasing a sensitivity of the optical sensor to increase a sensing value change range of the optical sensor;

[0024] Step c12) performing sensing on the storage tank without print material to obtain the first empty tank sensing value; and

[0025] Step c13) determining that the optical sensor is valid for the empty tank when the first empty tank sensing value meets the first empty tank critical condition.

[0026] In an embodiment, the third sensing value comprises a light transmission sensing value, and the third critical condition comprises a light transmission critical condition;

[0027] wherein the step c) further comprises:

[0028] a step c21) performing sensing on the storage slot with the transparent print material to obtain the transparent sensing value; and

[0029] a step c22) determining that the optical sensor is valid for the transparent print material when the transparent sensing value meets the transparent critical condition.

[0030] In an embodiment, the second sensing value further comprises a second empty slot sensing value, and the second critical condition further comprises a second empty slot critical condition.

[0031] wherein the step c) further comprises:

[0032] a step c23) adjusting a resistance value of a variable resistor or an electronic impedance coupled to the photoelectric sensor to adjust the transparent sensing value when the transparent sensing value does not meet the transparent critical condition.

[0033] a step c24) performing sensing on the storage slot without the print material based on the resistance value to obtain the second empty slot sensing value when the adjusted transparent sensing value meets the transparent critical condition.

[0034] a step c25) determining that the optical sensor is valid for the transparent print material when the second empty slot sensing value meets the second empty slot critical condition; and

[0035] a step c24) determining that the optical sensor is invalid for the transparent print material when the adjusted transparent sensing value does not meet the transparent critical condition.

[0036] In an embodiment, the third sensing value comprises a particle sensing value, and the third critical condition comprises a particle critical condition.

[0037] wherein the step c) comprises:

[0038] a step c31) performing sensing on the storage slot with the particle print material to obtain the particle sensing value; and

[0039] a step c32) determining that the optical sensor is valid for the transparent print material when the particle sensing value meets the particle critical condition.

[0040] In an embodiment, the step c32) further comprises determining that the optical sensor is valid for the transparent print material when the particle sensing value meets the particle critical condition and passes a stability test.

[0041] wherein the stability test comprises:

[0042] Step c321) performing sensing on the storage tank without the print material to obtain a third empty tank sensing value;

[0043] Step c322) performing sensing on the storage tank with the particulate print material to obtain another particulate sensing value; and

[0044] Step c323) determining that the stability test is passed when the third empty tank sensing value meets the second critical condition and the another particulate sensing value meets the particulate critical condition.

[0045] In an embodiment, after the step c) and before the step d), further comprising:

[0046] Step g1) connecting the storage tank to a cleaning solvent tank and a waste tank through a pipeline;

[0047] Step g2) discharging all the print material from the storage tank;

[0048] Step g3) injecting cleaning solvent from the cleaning solvent tank to the storage tank through an adjusting device;

[0049] Step g4) discharging the cleaning solvent from the storage tank to the waste tank through the adjusting device;

[0050] Step g5) repeating the step g3) and the step g4) for a preset cleaning number of times; and

[0051] Step g6) removing the cleaning solvent tank and the waste tank.

[0052] In an embodiment, after the step g6) and before the step d), further comprising:

[0053] Step h1) connecting the storage tank to a gas blowing device through a pipeline;

[0054] Step h2) continuously delivering a pressurized gas to the storage tank through the gas blowing device and the pipeline for a first preset gas supply time to dry the storage tank;

[0055] Step h3) after stopping the gas supply, continuously delivering a pressurized gas to the storage tank through the gas blowing device and the pipeline for a second preset gas supply time to dry the storage tank, wherein the second preset gas supply time is shorter than the first preset gas supply time; and

[0056] Step h4) removing the gas blowing device.

[0057] In an embodiment, after the step c) and before the step d), further comprising:

[0058] Step i1) assembling a liquid level control board, the storage tank, an adjusting device, a main storage tank and a printing device, wherein the liquid level control board comprises two optical sensors effective for liquid level detection, one of the optical sensors is set at a lower limit position of the liquid level of the storage tank as a lower limit sensor, the other of the optical sensors is set at an upper limit position of the liquid level of the storage tank as an upper limit sensor, and the storage tank is a secondary storage tank;

[0059] Step i2) determining the fourth critical condition of the lower limit sensor based on the second sensing value to sense whether the liquid level of the printing material is lower than the lower limit sensor; and

[0060] Step i3) determining the fourth critical condition of the upper limit sensor based on the third sensing value to sense whether the liquid level of the printing material is higher than the upper limit sensor.

[0061] In an embodiment, the step e) comprises:

[0062] Step e1) when the fourth sensing value of the lower limit sensor meets the fourth critical condition, controlling the adjusting device to start injecting the printing material from the main storage tank to the secondary storage tank; and

[0063] Step e2) when the fourth sensing value of the upper limit sensor meets the fourth critical condition, controlling the adjusting device to stop injecting the printing material from the main storage tank to the secondary storage tank.

[0064] In an embodiment, the optical sensor is an infrared sensor;

[0065] The sensing process of the optical sensor comprises:

[0066] Step j1) controlling a light emitter of the optical sensor to emit an infrared ray; and

[0067] Step j2) measuring a voltage value triggered by the reflected infrared ray received by a light receiver of the optical sensor as a sensing value.

[0068] In an embodiment, the first critical condition comprises that the first sensing value is greater than a first critical value, the second critical condition comprises that the second sensing value is greater than a second critical value, and the first critical value is less than the second critical value;

[0069] The third critical condition comprises that the third sensing value is less than a third critical value, and the third critical value is less than the first critical value.

[0070] In an embodiment, a liquid level control board is arranged on the storage tank and comprises a plurality of optical sensors, a voltage follower circuit and a Schmitt trigger;

[0071] wherein outputs of the plurality of optical sensors are coupled to the voltage follower circuit, and an output of the voltage follower circuit is coupled to the Schmitt trigger;

[0072] wherein a sensing process of the optical sensor comprises:

[0073] Step k1) generating a voltage signal triggered by the infrared light reflected by the optical sensor output;

[0074] Step k2) performing an analog noise filtering process on the voltage signal by the voltage follower circuit to filter out an analog noise (noise) from the voltage signal; and

[0075] Step k3) performing a compensation process on the filtered voltage signal by the Schmitt trigger to compensate the voltage signal for errors caused by the print material remaining on the wall surface of the storage tank.

[0076] The present application can avoid sensing errors caused by inapplicable optical sensors, and effectively maintain the liquid level of the storage tank at a normal liquid level. BRIEF DESCRIPTION OF DRAWINGS

[0077] Figure 1 A schematic diagram of a detection jig according to an embodiment of the present application.

[0078] Figure 2 A detection schematic diagram of an automatic feeding apparatus according to an embodiment of the present application.

[0079] Figure 3 A cleaning schematic diagram of an automatic feeding apparatus according to an embodiment of the present application.

[0080] Figure 4 A drying schematic diagram of an automatic feeding apparatus according to an embodiment of the present application.

[0081] Figure 5 An application schematic diagram of an automatic feeding apparatus according to an embodiment of the present application.

[0082] Figure 6 A first sensing schematic diagram of an optical sensor according to an embodiment of the present application.

[0083] Figure 7 A second sensing schematic diagram of an optical sensor according to an embodiment of the present application.

[0084] Figure 8 A circuit schematic diagram of an optical sensor according to an embodiment of the present application.

[0085] Figure 9 A flowchart of a detection method according to an embodiment of the present application.

[0086] Figure 10Flow chart of the first sensing process of an embodiment of the present application.

[0087] Figure 11 Flow chart of the empty slot sensing process of an embodiment of the present application.

[0088] Figure 12 Flow chart of the light-transmissive print material sensing process of an embodiment of the present application.

[0089] Figure 13 Flow chart of the particulate print material sensing process of an embodiment of the present application.

[0090] Figure 14 Flow chart of the pre-application process of an embodiment of the present application.

[0091] Figure:

[0092] 1: detection jig; 10: stage; 100: detachable connection module; 101: optical sensor; 102: fixing structure; 11: liquid level control panel; 12: power supply device; 13: measuring device; 14: slot object; 2: automatic feeding device; 20: liquid level control panel; 201-203: optical sensor; 204: processing module; 205: storage module; 206: communication module; 21: storage tank; 210: wall surface; 22: adjusting device; 23: material tank; 24-26: pipeline; 3: automatic feeding device; 30: cleaning solvent tank; 31: waste liquid tank; 32-34, 37: pipeline; 35-36: electromagnetic valve; 4: automatic feeding device; 40: inflating device; 41-43: pipeline; 5: automatic feeding device; 50: adjusting device; 51: secondary storage tank; 52: printing device; 53: main storage tank; 60: light-transmissive print material; 70: particulate print material; 80: optical sensor; 81: voltage follower circuit; 82: Schmitt trigger; D1-D11: flow direction; C11, C21: capacitor; R11, R12, R21-R23, R31-R34: resistor; Vcc, Vso, Vfo, Vco: voltage; S1: selection stage; S10-S13 selection step; S2: plate-up stage; S20-S23 plate-up detection step; S3: application stage; S30-S33 liquid level detection step; S40-S42 first sensing step; S50-S54 empty slot sensing step; S60-S66 light-transmissive print material sensing step; S70-S75 light-transmissive print material sensing step; S80-S84 pre-application step. DETAILED DESCRIPTION

[0093] The present application will be further described with reference to the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it.

[0094] The present application mainly proposes a storage tank liquid level detection method, which can exclude optical sensors with hardware defects or other factors that are not suitable for liquid level detection through first sorting processing before the selection stage, ensure that the optical sensors can correctly detect the material-free and material states and set appropriate critical conditions through second sorting processing at the upper plate stage, so as to correctly perform liquid level detection at the application stage to adjust the liquid level of the printing material.

[0095] Please refer to Figure 6 The first sensing schematic diagram of the optical sensor of an embodiment of the present application is used to illustrate how the optical sensor of the present application is applied to the liquid level detection of the printing material.

[0096] The present application can be provided with multiple optical sensors 201-203 on the storage tank 21, and each optical sensor 201-203 corresponds to a different liquid level grade. The number of liquid level grades, i.e., the number of optical sensors 201-203, can be arbitrarily changed according to requirements, and the number of optical sensors of the present application is not limited by this.

[0097] For example, the optical sensor 201 is arranged at the lowest liquid level lower limit position as a liquid level lower limit sensor. When the optical sensor 201 does not detect the printing material, it indicates that the remaining capacity of the printing material is too small, and the printing material must be injected. When the optical sensor 201 detects the printing material, it indicates that the remaining capacity of the printing material is sufficient.

[0098] The optical sensor 202 is arranged at the second highest liquid level upper limit position as a liquid level upper limit sensor. When the optical sensor 202 does not detect the printing material, it indicates that the remaining capacity of the printing material is sufficient, and the printing material injection can be stopped, and the printing program can be started or continued. When the optical sensor 202 detects the printing material, it indicates that the remaining capacity of the printing material is too large.

[0099] The optical sensor 203 is arranged at the highest safety liquid level position as a safety liquid level sensor. When the optical sensor 203 does not detect the printing material, it indicates that the remaining capacity of the printing material will not cause backflow. When the optical sensor 203 detects the printing material, it indicates that the remaining capacity of the printing material is more than the safety upper limit, and there is a risk of printing material backflow (such as backflow from the upper pipeline to the air pressure system).

[0100] In an embodiment, the optical sensor can be an infrared sensor, and includes a light emitter (such as an infrared emitting LED), a light receiver (such as a phototransistor that receives light signals), and an amplification driving circuit (not necessary).

[0101] Furthermore, the optical sensors 201-203 can perform sensing processing to obtain a sensed value. The sensing processing may include: emitting infrared light through a light emitter; and measuring the voltage value of the photovoltage triggered by the reflected infrared light received by the light receiver as the sensed value.

[0102] In one embodiment, the optical sensors 201-203 may be modified to be disposed inside the storage tank 21. For example, a light-transmitting and waterproof protective shell (such as transparent acrylic) may be used to cover the optical sensors 201-203, and the covered optical sensors 201-203 may be disposed on the inner wall.

[0103] In one embodiment, the light emitter may be disposed on the inner wall and the light receiver may be disposed on the outer wall, thereby reducing energy loss by reducing the number of times the light penetrates the wall 210.

[0104] In one embodiment, the wall 210 of the storage tank 21 may be made wholly or partially (e.g., only at the location where the optical sensors 201-203 are installed) of a light-transmitting material, such as highly transparent glass or highly transparent acrylic, so that the sensing light (e.g., infrared light) of the optical sensors 201-203 can penetrate the wall 210 to sense the liquid level on the inner wall.

[0105] like Figure 6 As shown, taking the optical sensor 202 as an example, when there is no printing material, the sensing light that penetrates the solid wall 210 comes into contact with the air and undergoes total internal reflection (the incident angle is greater than the critical angle of total internal reflection), thus triggering a higher photovoltage (such as 2.8V).

[0106] When the storage tank 21 stores printing material, such as the light-transmitting printing material 60, it can be a high-transmittance printing material (e.g., 70% or more) such as transparent ink or high-transmittance colored ink. Taking the optical sensor 201 as an example, the sensing light that penetrates the solid wall 210 will come into contact with the liquid printing material. Due to the similar density, it will be refracted in the light-transmitting printing material 60. Only a small amount of sensing light will be reflected, triggering a low photovoltage (e.g., less than 1 V).

[0107] By utilizing the aforementioned characteristics of photovoltage variation, the present invention can distinguish whether each optical sensor 201-203 has detected the printing material.

[0108] Please see Figure 8 This is a circuit architecture diagram of an optical sensor according to an embodiment of the present invention. The present invention proposes to install one or more optical sensors 80 on a liquid level control plate.

[0109] A liquid level control plate is used to mount on the storage tank and may further include a voltage follower circuit 81 and a Schmitt trigger 82. The outputs of each optical sensor 80 are coupled to the voltage follower circuit 81, and the outputs of the voltage follower circuit 81 are coupled to the Schmitt trigger 82.

[0110] In one embodiment, each optical sensor 80 can be coupled with a variable resistor or an electronic impedance.

[0111] In one embodiment, the sensing process of the optical sensor 80 includes the following steps: outputting a voltage signal triggered by the reflected infrared light from the optical sensor 80; performing an analog noise filtering process on the voltage signal by the voltage follower circuit 81 to filter out analog noise from the voltage signal; and performing a compensation process on the filtered voltage signal by the Schmitt trigger 82 to compensate the voltage signal for the error caused by the print material remaining on the wall of the storage tank.

[0112] The voltage follower circuit 81 and the Schmitt trigger 82 are existing circuit elements, and their specific principles and structures are not described again. The main progress of the present application is to apply the voltage follower circuit 81 and the Schmitt trigger 82 to the liquid level detection.

[0113] Please refer to Figure 9 for the flowchart of the detection method of one embodiment of the present application. The liquid level detection method of the present application includes a selection stage S1, a plate-up stage S2, and an application stage S3.

[0114] First, the selection stage S1 is described. Please refer to Figure 1 for the structural diagram of the detection jig of one embodiment of the present application. The selection stage S1 mainly applies the detection jig 1 to quickly eliminate unsuitable optical sensors 101.

[0115] In one embodiment, the detection jig 1 includes a carrier 10, a liquid level control board 11, a measuring device 13, and a power supply device 12.

[0116] The carrier 10 includes a detachable connection module 100 and a fixing structure 102.

[0117] The detachable connection module 100, such as a solderless breadboard, is used to couple the liquid level control board 11 and one or more optical sensors 101.

[0118] In the present application, the user only needs to insert / remove the optical sensor 101 into / from the detachable connection module 100, so that the optical sensor 101 can be quickly coupled / disconnected from the liquid level control board 11, and the detection can be quickly performed.

[0119] The fixing structure 102, such as a dowel, a clamp, or other fixable structure, is used to fix the carrier to a tank object 14. The tank object 14 simulates the light transmission condition of the storage tank. For example, the tank object 14 can have the same or similar light transmission rate, thickness, or material as the storage tank, and has a small volume to facilitate detection.

[0120] In one embodiment, the storage tank can be practically applied as the tank object 14 without limitation.

[0121] In the present application, by adjusting the setting position of the detachable connection module 100 and the fixed structure 102, when the fixed structure 102 is fixed to the tank object 14, all the optical sensors 101 coupled to the detachable connection module 100 can be directed to sense the tank object 14.

[0122] The liquid level control board 11 is used to supply power to the optical sensors 101 to emit infrared rays and receive the voltage signal of the photoelectric voltage of the optical sensors 101.

[0123] The measuring device 13 coupled to the liquid level control board 11 is used to measure the voltage value of the photoelectric voltage of the optical sensors 101 as the sensing value.

[0124] In one embodiment, the measuring device 13 (such as a multimeter) can be coupled to the detachable connection module 100 to directly measure the sensing value from the detachable connection module 100.

[0125] The power supply device 12 coupled to the liquid level control board 11 is used to provide power, such as 3.3V direct current power.

[0126] Referring to Figure 9 , the selection stage S1 can include steps S10-S13.

[0127] Step S10: The optical sensor 101 is coupled to the detachable connection module 100, and the detection tool 1 is operated to perform the first sensing process. Specifically, the tank object 14 is sensed by the optical sensor 101, and the sensing value (first sensing value) of the optical sensor 101 is obtained by the measuring device 13.

[0128] Step S11: Determine whether the first sensing value meets the preset critical condition (first critical condition).

[0129] In one embodiment, the first critical condition can include that the first sensing value is greater than a first critical value (such as 2.3V) or falls within a first critical range (such as 2V-3V).

[0130] If the first sensing value meets the first critical condition, step S12 is performed: determining that this optical sensor 101 is for liquid level detection, i.e., passing the first sorting process.

[0131] If the first sensing value does not meet the first critical condition, step S13 is performed: determining that this optical sensor 101 is for other purposes, such as personnel detection or other non-liquid level detection purposes.

[0132] It is worth mentioning that the optical sensors 101 eliminated in the first sorting process can be eliminated due to hardware defects or due to not meeting the strict requirements of the liquid level detection. In this case, these eliminated optical sensors 101 can still be used for other low sensitivity requirements, thereby avoiding waste.

[0133] Next, the next optical sensor 101 can be selected, and the first sorting process can be performed again on the next optical sensor 101 by executing steps S10-S13 until all optical sensors 101 complete detection.

[0134] Next, the upper plate stage S2 is described with reference to Figure 2 FIG. 1 is a schematic diagram of a detection of an automatic feeding device according to an embodiment of the present application. The upper plate stage S2 mainly uses the automatic feeding device 2 to detect the detection ability of the optical sensors 201-203 for the liquid level detection for the material without the material and the material.

[0135] The automatic feeding device 2 includes a liquid level control panel 20, a storage tank 21, an adjusting device 22, and a material tank 23 for storing the printing material.

[0136] The optical sensors 201-203 determined to be used for the liquid level detection in the elimination stage S1 are welded / adhered to the liquid level control panel 20. The liquid level control panel 20 can be installed on the wall of the storage tank 21 to monitor different liquid levels and control the adjusting device 22 to make corresponding adjustment actions.

[0137] The adjusting device 22, such as a pump, is electrically connected to the liquid level control panel 20 to receive control. The adjusting device 22 is connected to the material tank 23 through the pipeline 25 and connected to the storage tank 21 through the pipeline 26.

[0138] When the adjusting device 22 is operated in the forward direction, the printing material can be injected from the material tank 23 to the storage tank 21 along the flow direction D1 through the pipelines 25, 26, and when the adjusting device 22 is operated in the reverse direction, the printing material can be extracted from the storage tank 21 to the material tank 23 along the flow direction D2 through the pipelines 26, 25, thereby adjusting the liquid level of the storage tank 21.

[0139] In an embodiment, the storage tank 21 is also connected to the material tank 23 through the pipeline 24, so that the excess printing material can flow back to the material tank 23 along the flow direction D3 through the pipeline 24.

[0140] Referring to Figure 9 The upper plate stage S2 can include steps S20-S23.

[0141] Step S20: performing the second sensing process by the liquid level control panel 20.

[0142] In one embodiment, the second sensing process is to control the adjustment device 22 to draw out the print material from the storage tank 21 to create a print material-free storage tank 21, sense it to obtain a print material-free sensing value (second sensing value), and control the adjustment device 22 to inject print material into the storage tank 21 to create a print material-full storage tank 21, sense it to obtain a print material-full sensing value (third sensing value).

[0143] Step S21: Determine whether the sensing value meets the critical condition. Specifically, determine whether the second sensing value meets a preset second critical condition corresponding to the print material-free condition, and determine whether the third sensing value meets a preset third critical condition corresponding to the print material-full condition.

[0144] In one embodiment, the second critical condition can include that the second sensing value is greater than a second critical value (e.g., 2.4 V) or falls within a second critical range (e.g., 2.4 V-2.8 V).

[0145] In one embodiment, the first critical value can be less than the second critical value.

[0146] In one embodiment, the third critical condition can include that the third sensing value is less than a third critical value (e.g., 1.5 V) or falls within a third critical range (e.g., 1.2 V-1.5 V).

[0147] In one embodiment, the third critical value can be less than the first critical value.

[0148] If the second sensing value meets the second critical condition and the third sensing value meets the third critical condition, step S22 is performed: determine that the optical sensors 201-203 on the liquid level control board 20 are effective for liquid level detection.

[0149] If the second sensing value does not meet the second critical condition or the third sensing value does not meet the third critical condition, step S23 is performed: adjust the parameters or replace the optical sensors 201-203.

[0150] In one embodiment, the liquid level control board 20 includes a variable resistor or an electronic resistor. The user can first adjust the sensitivity of the optical sensors 201-203 through the variable resistor or the electronic resistor to try to make the sensing value meet the critical condition.

[0151] If the sensing value cannot be made to meet the critical condition by adjustment, the optical sensor 201-203 that does not meet the critical condition can be removed (e.g., de-soldered or removed by adhesive) from the liquid level control board 20 and replaced with another optical sensor that passes the first sorting process.

[0152] In this way, through the first sorting process and the second sorting process, the present application can ensure that the optical sensors 201-203 have correct liquid level detection capabilities.

[0153] Next, the application stage S3 is described with reference to Figure 5 Fig. 3 is a schematic diagram of the application of the automatic feeding device according to an embodiment of the present application. The application stage S3 mainly applies the automatic feeding device 5 to adjust the remaining capacity of the print material in real time according to the liquid level.

[0154] The plurality of optical sensors 201-203 installed on the liquid level control board 20 are subjected to two kinds of sorting processing. The liquid level control board 20 is installed in the secondary storage tank 51 (e.g., the small-capacity storage tank 21) to monitor different liquid levels through the plurality of optical sensors 201-203 and control the adjusting device 50 to make corresponding adjustment actions.

[0155] The adjusting device 50 is used to inject the print material from the primary storage tank 53 (e.g., the large-capacity material tank 23) to the secondary storage tank 51 (flow direction D10) or to extract the print material from the secondary storage tank 51 to the primary storage tank 53 (flow direction D11).

[0156] In an embodiment, the liquid level control board 20 further includes a storage module 205, a communication module 206, a printing device 52, and a processing module 204 electrically connected to the above-mentioned modules and the optical sensors 201-203.

[0157] The storage module 205, such as a flash memory, an EEPROM, or other non-volatile memory, is used to store data, such as storing critical conditions.

[0158] The communication module 206, such as a network module or a signal transceiver, is used to transmit control signals to the adjusting device 50.

[0159] The printing device 52, such as a print head, uses the print material in the secondary storage tank 51 to perform printing processing.

[0160] The processing module 204, such as a signal processing circuit, a microcontroller, a CPU, or other processors, is used to compare the sensing values with the corresponding critical conditions and generate control signals for the adjusting device 50 according to the comparison results.

[0161] Referring to Fig. 4, the application stage S3 can include steps S30-S33. Figure 9

[0162] Step S30: During the printing process, the liquid level control board 20 performs a sensing process (third sensing process) on the storage tank (i.e., the secondary storage tank 51) to obtain sensing values (fourth sensing values) of the optical sensors 201-203. The optical sensors 201-203 of the liquid level control board 20 are effective for liquid level detection through two kinds of sorting processing.

[0163] Step S31: Determine whether the fourth sensing values of the optical sensors 201-203 meet the preset fourth critical conditions. ​

[0164] In one embodiment, the fourth threshold condition corresponding to each optical sensor 201-203 is determined based on the detection result of the optical sensor 201-203 in the upper plate stage S2 and the set position.

[0165] For example, the optical sensor 201 as the lower limit liquid level sensor can set the fourth threshold condition based on the second sensing value of no printing material, so as to have the ability to detect from printing material to no printing material. The optical sensors 202, 203 as the upper limit liquid level sensor and the safety liquid level sensor can set the fourth threshold condition based on the third sensing value of printing material, so as to have the ability to detect from no printing material to printing material.

[0166] If the fourth sensing value meets the fourth threshold condition, step S32 is performed: control the adjusting device 50 to start or stop injecting printing material into the secondary storage tank 51.

[0167] In one embodiment, the present application starts to inject printing material into the secondary storage tank 51 (the lower limit liquid level sensor meets the fourth threshold condition), stops injecting printing material into the secondary storage tank 51 (the upper limit liquid level sensor meets the fourth threshold condition), or the secondary storage tank 51 extracts printing material to the main storage tank 53 (the safety liquid level sensor meets the fourth threshold condition).

[0168] If the fourth sensing value does not meet the fourth threshold condition or step S32 is completed, step S33 is performed: determine whether to end printing, such as completing all printing work or the user interrupting printing.

[0169] If it is determined to end printing, the method execution is ended; otherwise, continue printing and perform step S30 again.

[0170] Therefore, the present application can effectively detect the liquid level height for adjustment to avoid printing failure.

[0171] Please refer to Figure 1 , Figure 9 and Figure 10 . Figure 10 The flow chart of the first sensing process of one embodiment of the present application. The first sensing process of step S10 can include steps S40-S42.

[0172] Step S40: the optical sensor 101 is detachably installed on the detection jig 1 to perform optical sensing towards the tank object 14.

[0173] Step S41: the measuring device 13 is coupled to the optical sensor 101.

[0174] Step S42: the voltage value of the optical sensor 101 is obtained by the measuring device 13 as the first sensing value.

[0175] Please refer toFigure 9 With Figure 11 , Figure 11 a flowchart of the empty slot sensing process of an embodiment of the present application.

[0176] In this embodiment, the second sensing process of step S20 can include the empty slot sensing process of steps S50-S54. The empty slot sensing process is used to detect the resolution capability of the optical sensors 201-203 for the material-free storage slots 21. The second sensing value includes a first empty slot sensing value, and the second critical condition includes a first empty slot critical condition.

[0177] The empty slot sensing process of this embodiment includes the following steps.

[0178] Step S50: Increase the sensitivity of the optical sensors 201-203 to increase the sensing value variation range of the optical sensors 201-203.

[0179] In an embodiment, the sensitivity can be adjusted by a variable resistor or an electronic sensor as shown in FIG. 1, such as adjusting the resistance value to the highest. Figure 8

[0180] Step S51: Obtain a first empty slot sensing value by performing sensing on the material-free (empty or the liquid surface does not enter the sensing area of the optical sensors 201-203) storage slots 21 by the optical sensors 201-203.

[0181] Step S52: Determine whether the first empty slot sensing value meets the preset first empty slot critical condition.

[0182] In an embodiment, the first empty slot critical condition can be that the first empty slot sensing value is greater than a first empty slot critical value (such as 2.4 V) or falls within a first empty slot critical range (such as 2.4 V-2.8 V).

[0183] If the first empty slot sensing value meets the first empty slot critical condition, step S53 is performed: performing a material sensing process, such as performing the transparent print material sensing process of step S30 or the particulate print material sensing process of step S40. Figure 11 Figure 12

[0184] If the first empty slot sensing value does not meet the first empty slot critical condition, step S54 is performed: eliminating the non-compliant optical sensors 201-203, replacing another optical sensor, and performing step S50 again.

[0185] In this way, the optical sensors 201-203 that pass the above-mentioned material-free sensing process can effectively detect the material-free state.

[0186] Please refer to Figure 9 , Figure 11 and Figure 12 ,​​​Figure 12 Flowchart of the transparent print material sensing process of an embodiment of the present application.

[0187] In this embodiment, the second sensing process of step S20 can include the transparent print material sensing process of steps S60-S66. The transparent print material sensing process is used to detect the resolution capability of the optical sensors 201-203 for the transparent print material storing slots 21. The third sensing values include the transparent sensing values, and the third critical condition includes the transparent critical condition. Also, the second sensing values can include the second empty slot sensing values, and the second critical condition can include the second empty slot critical condition.

[0188] The transparent print material sensing process of this embodiment includes the following steps.

[0189] Step S60: Obtain the transparent sensing values by sensing the transparent print material storing slots 21 with the optical sensors 201-203.

[0190] Step S61: Determine whether the transparent sensing values meet the preset transparent critical condition.

[0191] In an embodiment, the transparent critical condition is that the transparent sensing values are less than a transparent critical value (e.g., 1.5 V) or fall within a transparent critical range (e.g., 1.2 V-1.5 V).

[0192] If the transparent sensing values meet the transparent critical condition, step S62 is performed to determine that the optical sensors 201-203 are effective for the transparent print material.

[0193] If the transparent sensing values do not meet the transparent critical condition, step S63 is performed to determine whether the adjusted transparent sensing values meet the transparent critical condition.

[0194] Specifically, the sensed transparent sensing values are adjusted by adjusting the resistance value of the variable resistor or electronic resistor (e.g., reducing the resistance value) to attempt to make the adjusted transparent sensing values meet the transparent critical condition.

[0195] If the transparent sensing values can meet the transparent critical condition through adjustment, step S64 is performed to obtain the second empty slot sensing values by sensing the empty print material storing slots 21 based on the adjusted resistance value.

[0196] Step S65: Determine whether the second empty slot sensing values meet the second empty slot critical condition.

[0197] In an embodiment, the second empty slot critical condition can be the same as or different from the aforementioned first empty slot critical condition.

[0198] If the adjusted second empty slot sensing values meet the second empty slot critical condition, step S62 is performed to determine that the optical sensors 201-203 are effective for the transparent print material.

[0199] If the light transmission sensing value cannot be adjusted to meet the light transmission critical condition, or the adjusted second slot sensing value does not meet the second slot critical condition, step S66 is performed to determine that the optical sensor 201-203 that does not meet the condition is invalid for the light transmission print material.

[0200] In this way, the optical sensor 201-203 in the light transmission print material sensing process can effectively detect the liquid level of the light transmission print material.

[0201] Referring to Figure 7 . Figure 7 The second sensing schematic diagram of the optical sensor of an embodiment of the present application is used to illustrate another problem solved by the present application. Print materials can generally be divided into Figure 6 light transmission print material 60 and Figure 7 particulate print material 70.

[0202] When the particulate print material 70, such as white ink or low light transmission colored ink, stored in the storage tank 21, has a low light transmission rate (e.g., less than 30%) due to a large number of low light transmission particles, most of the sensing light (e.g., optical sensor 201) will be reflected, triggering a high photoelectric voltage, such as greater than 2.8V.

[0203] However, when there is no print material (e.g., optical sensor 202), most of the sensing light will also be reflected, triggering a high photoelectric voltage, such as greater than 2.4V.

[0204] Because the difference in photoelectric voltage between the two states of no print material and particulate print material is very small (e.g., less than 1V), the current liquid level detection method using optical sensors cannot effectively distinguish between the two states.

[0205] Referring to Figure 9 and Figure 13 , Figure 13 The flowchart of the particulate print material sensing process of an embodiment of the present application.

[0206] To solve the above problem, in the present embodiment, the second sensing process of step S20 can include the particulate print material sensing process of steps S70-S75. The particulate print material sensing process is used to detect the resolution capability of the optical sensor 201-203 for the storage tank 21 with particulate print material. The third sensing value includes a particulate sensing value, and the third critical condition includes a particulate critical condition.

[0207] The particulate print material sensing process of the present embodiment includes the following steps.

[0208] Step S70: Perform sensing on the storage tank 21 with particulate print material by the optical sensor 201-203 to obtain a particulate sensing value.

[0209] Step S71: Adjusting the variable resistor or electronic impedance to make the particulate sensing value (first particulate sensing value) of the optical sensor 201-203 meet the particulate critical condition (e.g. falling within 1.2V-1.8V), and recording the adjusted particulate sensing value (e.g. falling within 1.2V-1.8V) and the resistance value.

[0210] Step S72: Adjusting the particulate sensing value of the optical sensor 201-203 to obtain an empty slot sensing value, and directly determining that the optical sensor 201-203 is invalid for particulate print material when the empty slot sensing value does not meet the second critical condition.

[0211] Step S73: Determine whether to pass the stability test.

[0212] In an embodiment, the stability test can include: performing sensing on the storage slot without print material to obtain an empty slot sensing value (third empty slot sensing value); performing sensing on the storage slot with particulate print material to obtain a particulate sensing value (second particulate sensing value); determining that the stability test is passed when the third empty slot sensing value meets the second critical condition and the second particulate sensing value meets the preset particulate critical condition, otherwise, determining that the stability test is not passed.

[0213] In an embodiment, the particulate critical condition can be that the particulate sensing value falls within a particulate critical range (e.g. 1.2V-1.8V).

[0214] In an embodiment, after obtaining the first particulate sensing value meeting the particulate critical range, the particulate critical condition in the stability test can be changed to that the particulate sensing value meets the particulate critical value (e.g. the first particulate sensing value). In other words, the stability test is to test whether the optical sensor 201-203 can keep stable sensing values (third empty slot sensing value and first particulate sensing value) for no print material and particulate print material.

[0215] If the stability test is passed, step S74 is performed: determining that the optical sensor 201-203 is valid for particulate print material.

[0216] If the stability test is not passed, step S75 is performed: determining that the optical sensor 201-203 is invalid for particulate print material.

[0217] In this way, the optical sensor 201-203 subjected to the above particulate print material sensing process can effectively detect the liquid level of the particulate print material.

[0218] It is worth mentioning that the stability test is not a necessary step of the present application, and when there is a need to shorten the detection time, the stability test can be omitted.

[0219] Please refer to Figure 14Fig. 2 is a flowchart of a pre-treatment process according to an embodiment of the present application. After the upper plate stage S2 is completed, before the application stage S3 is performed, the present application can perform steps S80-S83 to clean the storage tank and the pipeline, and to perform processing setting for each optical sensor.

[0220] Step S80: Perform a cleaning process on the storage tank and the pipeline to remove the print material remaining in the storage tank 21.

[0221] Please refer to Figure 3 Fig. 3 is a schematic diagram of a cleaning of an automatic feeding device according to an embodiment of the present application. The automatic feeding device 3 includes a cleaning solvent tank 30 for storing unused cleaning solvent and a waste tank 31 for storing used cleaning solvent. The aforementioned cleaning solvent can be 75%-100% alcohol or other high-volatility solvents, but is not limited thereto.

[0222] In an embodiment, the cleaning process can include the following steps: connecting the storage tank 21 to the cleaning solvent tank 30 through the pipeline 26, the regulating device 22, the pipeline 37, the electromagnetic valve 35, and the pipeline 34, connecting the storage tank 21 to the waste tank 31 through the pipeline 26, the regulating device 22, the pipeline 37, the electromagnetic valve 36, and the pipeline 33, and connecting the storage tank 21 to the waste tank 31 through the pipeline 32; opening the electromagnetic valve 36, closing the electromagnetic valve 35, and discharging all the print material from the storage tank 21 to the waste tank 31 through the regulating device 22 (flow directions D5, D6); injecting cleaning solvent from the cleaning solvent tank 30 to the storage tank 21 through the regulating device 22 (flow direction D4); waiting for a predetermined time, such as 5 minutes, which can be omitted; opening the electromagnetic valve 35, closing the electromagnetic valve 36, and discharging the cleaning solvent from the storage tank 21 to the waste tank 31 through the regulating device 22; repeating the above steps for a predetermined number of cleaning times, such as three times; and removing the cleaning solvent tank 30 and the waste tank 31.

[0223] Step S81: Perform a drying process on the storage tank and the pipeline to remove the print material remaining in the storage tank 21.

[0224] Please refer to Figure 4 Fig. 4 is a schematic diagram of a drying of an automatic feeding device according to an embodiment of the present application. The automatic feeding device 4 includes a gas filling device 40, such as an air compressor.

[0225] In one embodiment, the drying process can include the following steps: connecting the storage tank 21 to the air pump 40 through the pipeline 41; continuously supplying the pressurized gas to the storage tank 21 through the air pump 40 and the pipeline 41 for a first preset air supply time (e.g., 2 minutes) to dry the storage tank 21 and discharge the pressurized gas from the pipelines 42, 43 (flow directions D9, D8); after stopping the air supply, continuously supplying the pressurized gas to the storage tank 21 through the air pump 40 and the pipeline for a second preset air supply time (e.g., 1 minute) to dry the storage tank 21, the second preset air supply time can be shorter than or equal to the first preset air supply time, which is not limited; and removing the air pump 40.

[0226] Step S82: performing an assembly process.

[0227] Referring to Figure 5 The assembly process is to assemble the liquid level control panel 20, the secondary storage tank 51, the adjusting device 50, the main storage tank 53, and the printing device 52.

[0228] In one embodiment, the liquid level control panel 20 can include a lower limit liquid level sensor and an upper limit liquid level sensor (e.g., optical sensors 201-203 arranged at different positions).

[0229] Step S83: setting the fourth critical condition of the application stage S3.

[0230] In one embodiment, the fourth critical condition of the lower limit liquid level sensor can be determined based on the second sensing value to sense whether the liquid level of the printing material is lower than the lower limit liquid level sensor, and the fourth critical condition of the upper limit liquid level sensor can be determined based on the third sensing value to sense whether the liquid level of the printing material is higher than the upper limit liquid level sensor.

[0231] The above-described embodiments are only preferred embodiments of the present application for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent substitutions or transformations made by those skilled in the art based on the present application are within the protection scope of the present application. The protection scope of the present application is subject to the claims.

Claims

1. A method for detecting a liquid level in a storage tank, the method comprising: Comprising: Step a) performing a first sensing process on a tank object by an optical sensor to obtain a first sensing value, wherein the light transmittance of the tank object corresponds to the light transmittance of a storage tank, and the first sensing process comprises: Step a1) the optical sensor is detachably installed on a detection jig to perform optical sensing toward the tank object; Step a2) a measuring device is coupled to the optical sensor; and Step a3) a voltage value of the optical sensor is obtained by the measuring device as the first sensing value; Step b) when the first sensing value meets a first critical condition, determining that the optical sensor is for liquid level detection; Step c) performing a second sensing process on the storage tank by the optical sensor for liquid level detection to obtain a second sensing value without printing material and a third sensing value with printing material, and when the second sensing value meets a second critical condition and the third sensing value meets a third critical condition, determining that the optical sensor for liquid level detection is effective for liquid level detection; Step d) during a printing process, performing a third sensing process on the storage tank by the optical sensor effective for liquid level detection to obtain a fourth sensing value; and Step e) when the fourth sensing value meets a fourth critical condition, starting or stopping the injection of printing material into the storage tank, wherein the fourth critical condition corresponds to the second sensing value or the third sensing value.

2. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, Further comprising: Step f) when the first sensing value does not meet the first critical condition, determining that the optical sensor is not for liquid level detection.

3. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, The second sensing value comprises a first empty tank sensing value, and the second critical condition comprises a first empty tank critical condition; Wherein, the step c) comprises: Step c11) increasing the sensitivity of the optical sensor to increase the sensing value change range of the optical sensor; Step c12) performing sensing on the storage tank without printing material to obtain the first empty tank sensing value; and Step c13) when the first empty tank sensing value meets the first empty tank critical condition, determining that the optical sensor is effective for empty tank.

4. The method for detecting the liquid level in a storage tank as described in claim 3, characterized in that, The third sensing value comprises a light transmittance sensing value, and the third critical condition comprises a light transmittance critical condition; Wherein, the step c) further comprises: Step c21) performing sensing on the storage tank with light transmittance printing material to obtain the light transmittance sensing value; and Step c22) when the light transmittance sensing value meets the light transmittance critical condition, determining that the optical sensor is effective for light transmittance printing material.

5. The method for detecting the liquid level in a storage tank as described in claim 4, characterized in that, The second sensing value further comprises a second empty tank sensing value, and the second critical condition further comprises a second empty tank critical condition; Wherein, the step c) further comprises: Step c23) when the light transmittance sensing value does not meet the light transmittance critical condition, adjusting the resistance value of a variable resistor or an electronic impedance coupled to the optical sensor to adjust the light transmittance sensing value; Step c24) when the adjusted light transmittance sensing value meets the light transmittance critical condition, performing sensing on the storage tank without printing material based on the resistance value to obtain the second empty tank sensing value; Step c25) determining that the optical sensor is effective for the transparent print material when the second empty slot sensing value meets the second empty slot critical condition; and Step c24) determining that the optical sensor is ineffective for the transparent print material when the adjusted transparent sensing value does not meet the transparent critical condition.

6. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, The third sensing value includes a particle sensing value, and the third critical condition includes a particle critical condition; The step c) includes: Step c31) performing sensing on the storage slot with the particle print material to obtain the particle sensing value; and Step c32) determining that the optical sensor is effective for the transparent print material when the particle sensing value meets the particle critical condition.

7. The method for detecting the liquid level in a storage tank as described in claim 6, characterized in that, The step c32) further includes: determining that the optical sensor is effective for the transparent print material when the particle sensing value meets the particle critical condition and passes a stability test; The stability test includes: Step c321) performing sensing on the storage slot without print material to obtain a third empty slot sensing value; Step c322) performing sensing on the storage slot with the particle print material to obtain another particle sensing value; and Step c323) determining that the stability test is passed when the third empty slot sensing value meets the second critical condition and the another particle sensing value meets the particle critical condition.

8. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, After the step c) and before the step d), the method further includes: Step g1) connecting the storage slot to a cleaning solvent tank and a waste tank through a pipeline; Step g2) discharging all the print material from the storage slot; Step g3) injecting cleaning solvent from the cleaning solvent tank to the storage slot through an adjusting device; Step g4) discharging the cleaning solvent from the storage slot to the waste tank through the adjusting device; Step g5) repeating the step g3) and the step g4) for a preset cleaning number of times; and Step g6) removing the cleaning solvent tank and the waste tank.

9. The method for detecting the liquid level in a storage tank as described in claim 8, characterized in that, After the step g6) and before the step d), the method further includes: Step h1) connecting the storage slot to a gas blowing device through a pipeline; Step h2) continuously delivering a pressurized gas to the storage slot through the gas blowing device and the pipeline for a first preset gas supply time to dry the storage slot; Step h3) after stopping the gas supply, continuously delivering a pressurized gas to the storage slot through the gas blowing device and the pipeline for a second preset gas supply time to dry the storage slot, wherein the second preset gas supply time is shorter than the first preset gas supply time; and Step h4) removing the gas blowing device.

10. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, After the step c) and before the step d), the method further includes: i1) assembling a liquid level control board, the storage slot, an adjusting device, a main storage tank, and a printing device, wherein the liquid level control board includes two optical sensors which are effective for liquid level detection, one of the optical sensors is set at a lower liquid level position of the storage slot as a lower liquid level sensor, and the other optical sensor is set at an upper liquid level position of the storage slot as an upper liquid level sensor, and the storage slot is a secondary storage tank; i2) determining the fourth critical condition of the lower limit level sensor based on the second sensing value to sense whether the level of the print material is lower than the lower limit level sensor; and i3) determining the fourth critical condition of the upper limit level sensor based on the third sensing value to sense whether the level of the print material is higher than the upper limit level sensor.

11. The method for detecting the liquid level in a storage tank as described in claim 10, characterized in that, The step e) comprises: e1) controlling the adjusting device to start injecting the print material from the main storage tank to the sub storage tank when the fourth sensing value of the lower limit level sensor meets the fourth critical condition; and e2) controlling the adjusting device to stop injecting the print material from the main storage tank to the sub storage tank when the fourth sensing value of the upper limit level sensor meets the fourth critical condition.

12. The method for detecting the liquid level in a storage tank as described in claim 1, characterized in that, The optical sensor is an infrared sensor; The sensing process of the optical sensor comprises: j1) controlling a light emitter of the optical sensor to emit an infrared ray; and j2) measuring a voltage value triggered by the reflected infrared ray received by a light receiver of the optical sensor as a sensing value.

13. The method for detecting the liquid level in a storage tank as described in claim 12, characterized in that, The first critical condition comprises that the first sensing value is greater than a first critical value, the second critical condition comprises that the second sensing value is greater than a second critical value, and the first critical value is less than the second critical value; The third critical condition comprises that the third sensing value is less than a third critical value, and the third critical value is less than the first critical value.

14. The method for detecting the liquid level in a storage tank as described in claim 12, characterized in that, A level control board is arranged in the storage tank and comprises a plurality of optical sensors, a voltage follower circuit, and a Schmitt trigger; The outputs of the plurality of optical sensors are coupled to the voltage follower circuit, and the output of the voltage follower circuit is coupled to the Schmitt trigger. The sensing process of the optical sensor comprises: k1) outputting a voltage signal triggered by the reflected infrared ray by the optical sensor; k2) performing an analog noise filtering process on the voltage signal by the voltage follower circuit to filter out an analog noise from the voltage signal; and k3) performing a compensation process on the filtered voltage signal by the Schmitt trigger to compensate the voltage signal for errors caused by the print material remaining on the wall surface of the storage tank.

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