Light source control method, machine vision light source controller and industrial camera

Abstract

The present application relates to the technical field of machine vision systems, and to a method for controlling a light source, a machine vision light source controller, and an industrial camera. The method comprises: obtaining the exposure time of a camera and the shortest switching time of a light source, and receiving a stroboscopic signal sent by the camera; determining the lighting cycle of a PWM signal according to the stroboscopic signal, the exposure time, and the shortest switching time, and calculating the high-level time of lighting and the low-level time of lighting; calculating the lighting frequency of the PWM signal within the lighting cycle according to the high-level time of lighting and the low-level time of lighting; when the lighting frequency is not less than the idle frequency of the PWM signal of the idle cycle, and the high-level time and the low-level time are not less than the shortest switching time, controlling the light source to remain always on during the high-level time of lighting, and providing lighting for the camera. The method reduces the load of the light source in the always-on mode, and avoids the situation in which the light source is in a state of being turned off when the photosensitive chip is exposed in the stroboscopic mode.

Description

Technical Field

[0001] The present application relates to the technical field of machine vision systems, and further to a light source control method, a machine vision light source controller and an industrial camera. Background Art

[0002] There are two common ways for machine vision systems to control light sources. One is the constant light mode, that is, the light source is always on; the second is the stroboscopic mode, which turns on the light source only when a stroboscopic signal is received, and then turns off after a period of time, waiting for the next trigger. Among them, the constant light mode puts a heavy load on the light source and reduces the life of the light source. The stroboscopic mode cannot identify whether the photosensitive chip of the industrial camera is in an exposure state. As a result, the light source may be off when the photosensitive chip is exposed, thereby reducing the luminous flux during exposure. Summary of the invention

[0003] In order to solve the above technical problems, the present application provides a light source control method, a machine vision light source controller and an industrial camera, which reduce the load of the light source in the constant light mode and increase the service life of the light source.

[0004] In a first aspect, the present application provides a light source control method, which controls the light source to provide lighting when a camera is exposed through a PWM signal, comprising: obtaining the exposure time of the camera and the shortest switching time of the light source, and receiving a stroboscopic signal sent by the camera, wherein when the stroboscopic signal is not received, the period of the PWM signal is an idle period, and the light source controlled by the PWM signal is used to prevent the human eye from feeling the flicker of the light source during the idle period; determining the lighting period of the PWM signal according to the stroboscopic signal, the exposure time and the shortest switching time, and calculating the lighting high level time and the lighting high level time of the PWM signal within the lighting period; The method comprises the following steps: controlling the light source to keep on lighting during the lighting high level time and the lighting low level time, wherein the time when the PWM signal enters the lighting cycle is synchronized with the time when the camera starts exposure, the lighting high level time is greater than the exposure time, and the lighting duty cycle of the lighting cycle is equal to the idle duty cycle of the idle cycle; calculating the lighting frequency of the PWM signal within the lighting cycle according to the lighting high level time and the lighting low level time; and controlling the light source to remain on during the lighting high level time to provide lighting for the camera when the lighting frequency is not less than the idle frequency of the PWM signal in the idle cycle, and both the high level time and the low level time are not less than the shortest switching time.

[0005] The above light source control method determines the lighting cycle of the PWM signal after receiving the stroboscopic signal, and calculates the corresponding lighting high level time and lighting low level time, and the lighting high level time is greater than the exposure time, so that when the camera's photosensitive chip starts to be exposed, the light source is controlled to remain always on during the exposure time to provide lighting for the exposure process of the photosensitive chip. The load of the light source in the constant light mode is reduced, and the service life of the light source is increased; at the same time, the problem of the light source being in a state of being on and off when the photosensitive chip is exposed in the stroboscopic mode is avoided, thereby reducing the luminous flux during exposure.

[0006] In one implementation, it also includes: when the duty cycle of the PWM signal is not greater than a preset value, keeping the high level time of the PWM signal unchanged, and continuously reducing the low level time of the PWM signal until the human eye cannot feel the flicker of the light source; when the duty cycle of the PWM signal is greater than the preset value, keeping the low level time of the PWM signal unchanged, and continuously increasing the high level time of the PWM signal until the human eye cannot feel the flicker of the light source; using the PWM signal after the high level time or the low level time is adjusted as a non-inductive periodic PWM signal; calculating the idle high level time and the idle low level time according to the non-inductive duty cycle of the non-inductive periodic PWM signal and the shortest switching time; when the stroboscopic signal is not received, controlling the on and off of the light source by the idle high level time and the idle low level time of the PWM signal of the idle period, wherein the idle duty cycle is equal to the non-inductive duty cycle, the idle frequency is not less than the non-inductive frequency of the non-inductive periodic PWM signal, and the idle high level time and the idle low level time are not less than the shortest switching time.

[0007] The above light source control method dynamically adjusts the high level time and low level time according to the different duty cycles of the PWM signal, so that each type of PWM signal can be adjusted to a non-inductive periodic PWM signal, thereby improving the flexibility of the present application. At the same time, when no stroboscopic signal is received, the idle periodic PWM signal is used to control the on and off of the light source, thereby reducing unnecessary energy consumption.

[0008] In one implementation, the step of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time, and the shortest switching time, and calculating the lighting high level time and lighting low level time of the PWM signal within the lighting cycle, specifically includes: when the stroboscopic signal is received within the idle high level time, taking the current idle cycle as the lighting cycle, and recording the first duration of the PWM signal within the idle high level time; judging whether the sum of the first duration, the exposure time, and the shortest switching time is greater than the idle high level time; if not, calculating the lighting high level time according to the first duration and the idle high level time, and calculating the lighting low level time according to the insensitive duty cycle and the lighting high level time; if greater, calculating the lighting high level time according to the exposure time, the shortest switching time, and the first duration, and calculating the lighting low level time according to the insensitive duty cycle and the lighting high level time.

[0009] In one implementation, the method of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time and the shortest switching time, and calculating the lighting high level time and lighting low level time of the PWM signal within the lighting cycle, specifically includes: when the inductive duty cycle is greater than the preset value and the stroboscopic signal is received within the idle low level time, taking the next idle cycle of the current idle cycle as the lighting cycle, and recording the second duration of the PWM signal within the idle low level time of the current idle cycle; judging whether the sum of the second duration and the exposure time is greater than the idle high level time; if not, taking the idle high level time as the lighting high level time, and taking the idle low level time as the lighting low level time.

[0010] In one implementation, it also includes: if the sum of the second duration and the exposure time is greater than the idle high level time, calculating the lighting high level time according to the exposure time and the second duration; and calculating the lighting low level time according to the lighting high level time and the insensitive duty cycle.

[0011] In one implementation, the method of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time, and the shortest switching time, and calculating the lighting high level time and lighting low level time of the PWM signal within the lighting cycle specifically includes: when the insensitive duty cycle is not greater than the preset value and the stroboscopic signal is received within the idle low level time, taking the current idle cycle and the next idle cycle as the lighting cycle, and recording the second duration of the PWM signal within the idle low level time of the current idle cycle; when the second duration is not greater than the shortest switching time, controlling the PWM signal to maintain a low level state in the current idle cycle, and the holding time is the shortest switching time minus the second duration; after the low level state ends, the PWM signal is pulled up to a high level state in the next idle cycle, and the holding time of the high level state is the maximum value between the first holding time and the idle high level time, and the first holding time is the sum of the exposure time and the second duration; calculating the lighting high level time according to the holding time of the high level state and the shortest switching time; calculating the lighting low level time according to the lighting high level time and the insensitive duty cycle.

[0012] In one implementation, it also includes: when the first holding time is not less than the idle high level time, calculating the lighting high level time according to the first holding time and the shortest switching time; when the first holding time is less than the idle high level time, calculating the lighting high level time according to the idle high level time and the shortest switching time.

[0013] In one implementation, it also includes: when the second duration is greater than the shortest switching time, controlling the PWM signal to enter the high level of the next idle period, and the high level maintenance time in the next idle period is the sum of the exposure time and the shortest switching time; calculating the lighting high level time according to the sum of the exposure time and the shortest switching time and the idle high level time; calculating the lighting low level time according to the second duration and the inductive duty cycle.

[0014] The above light source control method can determine the lighting cycle of the corresponding PWM signal and calculate the high level time and low level time of the lighting cycle when receiving the stroboscopic signal under different circumstances, thereby improving the compatibility of the present application and user experience.

[0015] In a second aspect, the present application also provides a machine vision light source controller for controlling the on and off of a light source by implementing any of the light source control methods described above.

[0016] In a third aspect, the present application also provides an industrial camera for controlling the on and off of a light source by implementing any of the above light source control methods.

[0017] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0018] 1. After receiving the stroboscopic signal, the lighting cycle of the PWM signal is determined, and the corresponding lighting high level time and lighting low level time are calculated. The lighting high level time is greater than the exposure time, so that when the camera's photosensitive chip starts to be exposed, the light source is controlled to remain always on during the exposure time to provide lighting for the exposure process of the photosensitive chip. The load of the light source in the constant light mode is reduced, and the service life of the light source is increased; at the same time, the problem of the light source being in a state of being turned off when the photosensitive chip is exposed in the stroboscopic mode is avoided, thereby reducing the luminous flux during the exposure period.

[0019] 2. According to the different duty cycles of the PWM signal, the high level time and the low level time are dynamically adjusted, so that each type of PWM signal can be adjusted to a non-inductive periodic PWM signal, which improves the flexibility of the application. At the same time, when no stroboscopic signal is received, the idle periodic PWM signal is used to control the on and off of the light source, which can reduce unnecessary energy consumption.

[0020] 3. When receiving a stroboscopic signal under different circumstances, the lighting cycle of the corresponding PWM signal can be determined, and the high level time and low level time of the lighting cycle can be calculated. This improves the compatibility of the application and the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The preferred implementation modes will be described below in a clear and understandable manner with reference to the accompanying drawings to further illustrate the above-mentioned characteristics, technical features, advantages and implementation methods of the present invention.

[0022] Figure 1 A flow chart of a light source control method provided by an embodiment of the present application is shown;

[0023] Figure 2 A flow chart of generating a non-inductive periodic PWM signal provided by an embodiment of the present application is shown;

[0024] Figure 3 A flowchart of determining a lighting cycle of a PWM signal provided by an embodiment of the present application is shown;

[0025] Figure 4 A flowchart of determining a lighting cycle of a PWM signal provided by an embodiment of the present application is shown;

[0026] Figure 5 A flowchart of determining a lighting cycle of a PWM signal provided by an embodiment of the present application is shown;

[0027] Figure 6 A flow chart for determining a lighting cycle of a PWM signal provided by an embodiment of the present application is shown. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0029] In order to simplify the drawings, only the parts related to the invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0030] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0031] In this document, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0033] It should be noted that the above embodiments can be freely combined as needed. The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

[0034] Pulse Width Modulation (PWM) is a commonly used signal modulation technology, which is widely used in various electronic devices. It controls the duty cycle of the signal by changing the width of the pulse, thereby controlling the output signal.

[0035] In machine vision systems, LED light sources are often used to provide lighting for industrial cameras. Of course, other light sources can also be used to provide lighting for industrial cameras, such as but not limited to incandescent lamps, halogen lamps, etc., which can all be used by the present application. For ease of understanding, this application uses LED light sources to illustrate the details of the solution. The mode of controlling the LED light source is divided into a constant light mode and a stroboscopic mode. Among them, the control process of the stroboscopic mode is that after the industrial camera receives the external trigger signal for taking a photo given by the external sensor, it outputs an exposure signal to the photosensitive chip to start the exposure of the photosensitive chip; at the same time, it outputs a stroboscopic signal to the light source control module, so that it controls the LED light source to provide lighting during the exposure of the photosensitive chip. However, when the LED light source is controlled in the stroboscopic mode, the flickering frequency of the LED light source is low, resulting in the flickering of the LED light source in application scenarios similar to workshops being easily perceived by the human eye, thereby causing damage to the human eye. At this time, only the constant light mode can be selected, but the constant light mode will increase the load of the LED light source and reduce the life of the LED light source.

[0036] Therefore, in the stroboscopic mode, the LED light source can also be controlled by the PWM signal. When the PWM signal is at a high level, the LED light source is controlled to be on; when the PWM signal is at a low level, the LED light source is controlled to be off. Setting a specific duty cycle and a specific frequency for the PWM signal increases the flickering frequency of the LED light source under the control of the PWM signal. At this time, the LED light source is actually flickering, but because the human eye has a pause effect, when the flickering frequency is very high, the human eye cannot feel the flickering and thinks that the LED light source is always on. However, this method of controlling the LED light source with a PWM signal of a specific frequency and a specific duty cycle cannot distinguish whether the photosensitive chip of the industrial camera is in an exposure state. It may happen that when the photosensitive chip is exposed, the LED light source is in an off state, thereby reducing the luminous flux during exposure. To shoot an image of the same brightness, a longer exposure time is required, and a long exposure will cause motion smear when shooting moving objects. Therefore, the embodiment of the present application determines the lighting cycle of the PWM signal when receiving the stroboscopic signal, controls the time when the PWM signal enters the lighting cycle and the time when the photosensitive chip starts exposure, so that when the photosensitive chip starts to expose, the LED light source is in a lighting state, and the time when the LED light source is lit is greater than the exposure time, providing constant lighting for the industrial camera. At least one of the following beneficial effects can be achieved: the load of the LED light source is reduced and the service life of the LED light source is increased; it avoids the problem that the LED light source is in a state of being turned off when the photosensitive chip is exposed in the stroboscopic mode, thereby reducing the luminous flux during exposure.

[0037] The following is explained with reference to the accompanying drawings:

[0038] Reference Figure 1 , which shows a flow chart of a light source control method provided by an embodiment of the present application, such as Figure 1 As shown, including:

[0039] S100, obtaining the exposure time of the camera and the shortest switching time of the light source, and receiving the stroboscopic signal sent by the camera, wherein when the stroboscopic signal is not received, the period of the PWM signal is an idle period, and the light source controlled by the PWM signal is in the idle period, so that the human eye cannot feel the flicker of the light source.

[0040] S110, determining an illumination cycle of the PWM signal according to the strobe signal, the exposure time and the shortest switching time, and calculating an illumination high level time and an illumination low level time of the PWM signal within the illumination cycle, wherein the time when the PWM signal enters the illumination cycle is synchronized with the time when the camera starts exposure, the illumination high level time is greater than the exposure time, and the illumination duty cycle of the PWM signal within the illumination cycle is equal to the idle duty cycle of the PWM signal within the idle cycle.

[0041] S120, calculating the lighting frequency of the PWM signal within the lighting cycle according to the lighting high level time and the lighting low level time.

[0042] S130, when the lighting frequency is not less than the idle frequency of the PWM signal of the idle period, and both the lighting high level time and the lighting low level time are not less than the shortest switching time, control the light source to remain always on during the lighting high level time to provide lighting for the camera.

[0043] Different LED light source models have different shortest switching times. Many chips that provide power to LED light sources are DCDC power conversion chips, which have conversion frequencies themselves. Therefore, the shortest switching time of the LED light source can be determined based on the conversion frequency of the DCDC power conversion chip and the PWM signal path and other conditions (in the embodiment of the present application, Tswitch refers to the shortest switching time, and Tswitch will be directly used in the following formula).

[0044] The exposure time of the camera (or industrial camera, hereinafter referred to as camera) is different in different application scenarios (same as Tswitch, Texp will be directly used to refer to the exposure time in the formula, and the same applies to other parameters that appear later). When shooting a moving object, it is required that the distance moved by the image of the object on the photosensitive surface does not exceed one pixel within the exposure time, that is:

[0045] .

[0046] When the camera's stroboscopic signal is not received, the period of the PWM signal that controls the on and off of the LED light source is an idle period. The LED light source controlled by the idle period PWM signal has a flickering degree that cannot be perceived by the human eye, and the brightness of the LED light source meets the requirements of the luminous flux required for camera exposure. Among them, the idle high level time and the idle low level time of the idle period PWM signal affect the flickering degree of the LED light source; the duty cycle of the idle period PWM signal affects the brightness of the LED light source, and the higher the duty cycle, the brighter the LED light source. In addition, both the idle high level time and the idle low level time are not less than the shortest switching time (the shortest switching time is the time for the LED light source to switch between the two states of lighting and extinguishing. In fact, the shortest switching time is the time for the light source to switch between the two states of lighting and extinguishing. It is just that the light source in the embodiment of the present application is an example of an LED light source. If the light source is other light sources, there is also a corresponding shortest switching time). The shortest switching time in the PWM signal can be the time required for high and low level switching. For example, if the idle low level time and / or the idle low level time are less than the shortest switching time, the PWM signal cannot normally realize the lighting and extinguishing state of the LED light source.

[0047] After the camera receives the external trigger signal (or photo signal) from the external sensor, it outputs an exposure signal to the photosensitive chip to start the exposure of the photosensitive chip; at the same time, it outputs a strobe signal to the light source control module. The light source control module determines the lighting cycle of the PWM signal based on the strobe signal, exposure time and shortest switching time, and calculates the lighting high level time and lighting low level time of the PWM signal within the lighting cycle. Before the PWM signal enters the lighting cycle, the light source control module also determines the strobe delay (the time from receiving the strobe signal to the PWM signal entering the lighting cycle), and sends the strobe delay to the camera to determine the corresponding exposure delay, so that the time when the PWM signal enters the lighting cycle is synchronized with the time when the photosensitive chip starts exposure.

[0048] If the lighting frequency is not less than the idle frequency, the LED light source controlled by the lighting cycle PWM signal will not flicker to a degree that can be perceived by the human eye. If both the lighting high level time and the lighting low level time are not less than the shortest switching time, the lighting cycle PWM signal can normally turn the LED light source on and off. If the lighting duty cycle is equal to the idle duty cycle, the brightness of the LED light source controlled by the lighting cycle PWM signal meets the requirements of the luminous flux required for camera exposure.

[0049] Therefore, when the lighting frequency, lighting duty cycle, lighting high level time and lighting low level time all meet the requirements, the PWM signal (the PWM signal is high level and low level in sequence within one cycle) can control the LED light source to remain always on during the lighting high level time after entering the lighting cycle, thereby providing lighting for the exposure process of the camera's photosensitive chip.

[0050] The embodiment of the present application determines the lighting cycle of the PWM signal after receiving the stroboscopic signal, and calculates the corresponding high-level lighting time and low-level lighting time, and the high-level lighting time is greater than the exposure time, so that when the camera's photosensitive chip starts to be exposed, the LED light source is controlled to remain always on during the exposure time to provide lighting for the exposure process of the photosensitive chip. The load of the LED light source in the always-on mode is reduced, and the service life of the LED light source is increased; at the same time, the problem of the LED light source being in a state of being on and off when the photosensitive chip is exposed in the stroboscopic mode is avoided, thereby reducing the luminous flux during exposure.

[0051] The idle cycle PWM signal is a form of the non-sensitive cycle PWM signal. The LED light source controlled by the non-sensitive cycle PWM signal will not flicker to the human eye. The frequency of the non-sensitive cycle PWM signal is the lowest frequency that satisfies the LED light source flicker level that cannot be perceived by the human eye. The duty cycle of the non-sensitive cycle PWM signal is the duty cycle that satisfies the luminous flux required for camera exposure. Both the idle frequency and the lighting frequency are not less than the frequency of the non-sensitive cycle PWM signal. Both the idle duty cycle and the lighting duty cycle are equal to the duty cycle of the non-sensitive cycle PWM signal. Figure 2 , which shows a flow chart of generating a non-inductive periodic PWM signal provided by an embodiment of the present application. Figure 2 As shown, including:

[0052] S200, when the duty cycle of the PWM signal is not greater than a preset value, the high level time of the PWM signal is kept unchanged, and the low level time of the PWM signal is continuously reduced until the human eye cannot perceive the flicker of the light source.

[0053] S210, when the duty cycle of the PWM signal is greater than a preset value, the low level time of the PWM signal is kept unchanged, and the high level time of the PWM signal is continuously increased until the human eye cannot perceive the flicker of the light source.

[0054] S220, using the PWM signal after the high level time or the low level time is adjusted as a non-inductive periodic PWM signal.

[0055] S230, calculating the idle high level time and the idle low level time according to the inductive duty cycle of the inductive periodic PWM signal and the shortest switching time.

[0056] S240, when no stroboscopic signal is received, the light source is controlled by the idle high level time and idle low level time of the idle period PWM signal, wherein the idle duty cycle is equal to the inductive duty cycle, the idle frequency is not less than the inductive frequency of the inductive period PWM signal, and the idle high level time and the idle low level time are not less than the shortest switching time.

[0057] The minimum frequency of the PWM signal that the human eye cannot feel flickering is different when the LED light source is on for different lighting times. The high level time of the PWM signal can be Texp+k*Tswitch. In the process of generating the PWM signal, the high level time of the PWM signal can be set to Texp+2*Tswitch, the low level time can be set to TLow_max, and TLow_max is greater than the shortest switching time.

[0058] When the duty cycle of the PWM signal is not greater than the preset value (which can be 50%), the high level time is kept unchanged, and the low level time of the PWM signal is continuously reduced until the human eye can no longer perceive the flickering of the LED light source. At this time, the adjusted PWM signal can be used as a non-inductive periodic PWM signal.

[0059] That is, when TLow_max≥Texp+2*Tswitch, duty cycle≤50%:

[0060]

[0061] When the duty cycle of the PWM signal is greater than the preset value, the low level time of the PWM signal is kept unchanged, and the high level time of the PWM signal is continuously increased until the human eye can no longer perceive the flicker of the LED light source. At this time, the adjusted PWM signal can also be used as an inductive periodic PWM signal.

[0062] That is, when TLow_max<Texp+2*Tswitch, duty cycle>50%:

[0063]

[0064] The high level time, low level time, duty cycle and frequency of the non-inductive periodic PWM signal are defined as non-inductive high level time (Ton_acpt), non-inductive low level time (Toff_acpt), non-inductive duty cycle (Dacpt) and non-inductive frequency (Factp). The formulas are:

[0065]

[0066]

[0067]

[0068]

[0069] The high level time, low level time, duty cycle and frequency of the idle period PWM signal are defined as the idle high level time (Ton_idle), idle low level time (Toff_idle), idle duty cycle (Didle) and idle frequency (Fidle) respectively. The idle duty cycle is set equal to the insensitive duty cycle, so that the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by the insensitive period PWM signal. The idle frequency is not less than the insensitive frequency, so that the brightness and flickering degree of the LED light source perceived by the human eye is acceptable. Both the idle high level time and the idle low level time are not less than the shortest switching time.

[0070] When the inductive duty cycle is not greater than the preset value, the idle high level time is set as the shortest switching time, and the idle low level time is calculated based on the inductive duty cycle and the idle high level time. The formula is as follows:

[0071]

[0072]

[0073] Because Dacpt≤50%, Toff_idle≥Ton_idle=Tswitch, that is, the idle low level time is not less than the shortest switching time. At this time, the idle duty cycle (Didle) is equal to the insensitive duty cycle (Dacpt), and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an insensitive periodic PWM signal.

[0074]

[0075] The idle high level time (Ton_idle) is less than the insensitive high level time (Ton_acpt), so the idle frequency (Fidle) must be greater than the insensitive frequency (Facpt). At this time, the flickering degree of the LED light source is acceptable.

[0076] When the inductive duty cycle is greater than the preset value, the idle low level time is set to the shortest switching time, and the idle low level time is calculated based on the inductive duty cycle and the idle low level time. The formula is as follows:

[0077]

[0078]

[0079] Because Dacpt>50%, Ton_idle>Toff_idle=Tswitch, that is, the idle high level time is greater than the shortest switching time. At this time, the idle duty cycle (Didle) is equal to the insensitive duty cycle (Dacpt), and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an insensitive periodic PWM signal.

[0080]

[0081] The idle low-level time (Toff_idle) is less than the inductive low-level time (Toff_acpt), so the idle frequency (Fidle) must be greater than the inductive frequency (Facpt). At this time, the flickering degree of the LED light source is acceptable.

[0082] It can be proved that:

[0083] When Dacpt≤50%, TLow_max≥Texp+2*Tswitch, K=2,

[0084]

[0085] When Dacpt>50%, TLow_max<Texp+2*Tswitch, Toff_idle=Tswitch, then:

[0086]

[0087] Substituting the formula of Dacpt and K, it can be proved that the above formula is equal to 0, that is, the idle high level time:

[0088]

[0089] That is to say, no matter what the situation is, the following equation is satisfied:

[0090]

[0091] Once the idle high level time (Ton_idle) and low level time (Toff_idle) are determined, the idle frequency (Fidle) is also determined. .

[0092] The embodiment of the present application dynamically adjusts the high level time and the low level time according to the different duty cycles of the PWM signal, so that each type of PWM signal can be adjusted to a non-inductive periodic PWM signal, thereby improving the flexibility of the present application. At the same time, when no stroboscopic signal is received, the idle periodic PWM signal is used to control the on and off of the LED light source, thereby reducing unnecessary energy consumption.

[0093] Reference Figure 3 , which shows a flow chart of determining the lighting cycle of a PWM signal provided by an embodiment of the present application. Figure 3 As shown, including:

[0094] S300, when a stroboscopic signal is received during the idle high level time, the current idle period is used as the lighting period, and the first duration of the PWM signal during the idle high level time is recorded.

[0095] S310, determining whether the sum of the first duration, the exposure time and the shortest switching time is greater than the idle high level time.

[0096] S320: If not greater than, calculate the lighting high level time according to the first duration and the idle high level time, and calculate the lighting low level time according to the insensitive duty cycle and the lighting high level time.

[0097] S330: If it is greater than, calculate the lighting high level time according to the exposure time, the shortest switching time and the first duration, and calculate the lighting low level time according to the insensitive duty cycle and the lighting high level time.

[0098] After receiving the stroboscopic signal, it is necessary to first determine the lighting cycle of the PWM signal, and control the LED light source within the lighting cycle to provide constant lighting for the exposure of the photosensitive chip. After the lighting cycle ends, the PWM signal is switched back to the idle cycle. The high level time, low level time, duty cycle and frequency of the lighting cycle PWM signal are defined as the lighting high level time (Ton_light), lighting low level time (Toff_light), lighting duty cycle (Dlight) and lighting frequency (Flight) respectively. Set the lighting duty cycle equal to the insensitive duty cycle so that the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by the insensitive period PWM signal. The lighting frequency is not less than the insensitive frequency, so that the flickering degree of the LED light source is acceptable to the human eye. At the same time, it is also necessary to ensure that the lighting high level time and the lighting low level time are not less than the shortest switching time.

[0099] When a strobe signal is received during the idle high level time, the current idle cycle is used as the lighting cycle, and the first duration (Thigh_high) of the PWM signal during the idle high level time is recorded. When the sum of the first duration, the exposure time, and the shortest switching time is not greater than the idle high level time, the PWM signal continues to be maintained in a high level state for at least Ton_idle-Thigh_high. The lighting high level time is calculated based on the maintenance time Ton_idle-Thigh_high and the first duration. The formula is as follows:

[0100]

[0101] At this time, the lighting high level time is the idle high level time. Then, the PWM signal is pulled down to the low level state, and the maintenance time is Toff_idle, that is, the lighting low level time is the idle low level time. The high level time, low level time of the lighting cycle and the high level time and low level time of the idle cycle are the same. Therefore, the lighting high level time and the lighting low level time must not be less than the shortest switching time, and the lighting duty cycle is equal to the idle duty cycle and the insensitive duty cycle. The brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by the insensitive period PWM signal. The lighting frequency is not less than the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0102] When the sum of the first duration, the exposure time and the shortest switching time is greater than the idle high level time, the PWM signal continues to be maintained in a high level state for at least Texp+Tswitch. The illumination high level time is calculated based on the maintenance time Texp+Tswitch and the first duration. The formula is as follows:

[0103]

[0104] Next, pull the PWM signal down to a low level state, and maintain it for a time of Toff_light. Calculate the low level time of lighting based on the high level time of lighting and the insensitive duty cycle. The formula is as follows:

[0105]

[0106]

[0107] The lighting duty cycle Dlight is equal to the inductive duty cycle Dacpt, and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an inductive periodic PWM signal.

[0108] Moreover, Ton_light=Texp+Tswitch+Thigh_high>Ton_idle, Dlight=Dacpt=Didle, then Toff_light>Toff_idle, and the lighting high level time and the lighting low level time are not less than the shortest switching time.

[0109]

[0110] The lighting high-level time is less than or equal to the insensitive high-level time, so the lighting frequency must be greater than or equal to the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0111] Therefore, when the lighting frequency, lighting duty cycle, lighting high level time and lighting low level time all meet the requirements, after the PWM signal enters the lighting cycle, it can control the LED light source to remain always on during the lighting high level time, thereby providing lighting for the exposure process of the camera's photosensitive chip.

[0112] Reference Figure 4 , which shows a flow chart of determining the lighting cycle of a PWM signal provided by an embodiment of the present application. Figure 4 As shown, including:

[0113] S400, when the inductive duty cycle is greater than a preset value and a strobe signal is received within the idle low level time, the next idle cycle of the current idle cycle is used as the lighting cycle, and the second duration of the PWM signal within the idle low level time of the current idle cycle is recorded.

[0114] S410, determining whether the sum of the second duration and the exposure time is greater than the idle high level time.

[0115] S420: If not, use the idle high level time as the lighting high level time, and use the idle low level time as the lighting low level time.

[0116] S430: If the sum of the second duration and the exposure time is greater than the idle high level time, calculate the illumination high level time according to the exposure time and the second duration.

[0117] S440, calculating the lighting low level time according to the lighting high level time and the inductive duty cycle.

[0118] When the inductive duty cycle is greater than the preset value and a strobe signal is received during the idle low level time, the second duration (Tlow_low) is recorded. At this time, the idle low level time is the shortest switching time, and Tlow_low≤Toff_idle=Tswitch. Wait in the current idle cycle for a waiting time of Tswitch-Tlow_low. After the current idle cycle ends normally, the next idle cycle is used as the lighting cycle. Calculate Texp+Tswitch. After the waiting time of Tswitch-Tlow_low, the remaining time is:

[0119]

[0120] Determine the sum of the second duration and the exposure time ( The second duration time and the exposure time are not greater than the idle high level time. If the sum of the second duration time and the exposure time is not greater than the idle high level time, the PWM signal is pulled high to the high level state, and the maintenance time is Ton_idle, that is, the lighting high level time is the idle high level time. Then, the PWM signal is pulled low to the low level state, and the maintenance time is Toff_idle, that is, the lighting low level time is the idle low level time. The high level time, low level time of the lighting cycle and the high level time and low level time of the idle cycle are the same. Therefore, the lighting high level time and the lighting low level time must not be less than the shortest switching time, and the lighting duty cycle is equal to the idle duty cycle and the insensitive duty cycle. The brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by the insensitive period PWM signal. The lighting frequency is not less than the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0121] If the sum of the second duration and the exposure time is greater than the idle high level time, the PWM signal is pulled up to the high level state, and the maintenance time is Texp+Tlow_low. The illumination high level time is calculated according to the exposure time and the second duration. The formula is as follows:

[0122]

[0123] Next, pull the PWM signal down to a low level state and maintain it for a time of Toff_light. Calculate the lighting low level time based on the lighting high level time and the insensitive duty cycle. The formula is as follows:

[0124]

[0125]

[0126] The lighting duty cycle Dlight is equal to the inductive duty cycle Dacpt, and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an inductive periodic PWM signal.

[0127] Moreover, Ton_light=Texp+Tlow_low>Ton_idle, Dlight=Dacpt=Didle, then Toff_light>Toff_idle, and the lighting high level time and the lighting low level time are not less than the shortest switching time.

[0128]

[0129] The lighting high-level time is less than or equal to the insensitive high-level time, so the lighting frequency must be greater than or equal to the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0130] Therefore, when the lighting frequency, lighting duty cycle, lighting high level time and lighting low level time all meet the requirements, after the PWM signal enters the lighting cycle, it can control the LED light source to remain always on during the lighting high level time, thereby providing lighting for the exposure process of the camera's photosensitive chip.

[0131] Reference Figure 5 , which shows a flow chart of determining the lighting cycle of a PWM signal provided by an embodiment of the present application. Figure 5 As shown, including:

[0132] S500, when the inductive duty cycle is not greater than the preset value and a strobe signal is received within the idle low level time, the current idle cycle and the next idle cycle are used as lighting cycles, and the second duration of the PWM signal within the idle low level time of the current idle cycle is recorded.

[0133] S510, when the second duration is not greater than the shortest switching time, control the PWM signal to maintain a low level state in the current idle period, and the maintenance time is the shortest switching time minus the second duration.

[0134] S520, after the low level state ends, the PWM signal is pulled up to the high level state in the next idle cycle, and the holding time in the high level state is the maximum value between the first holding time and the idle high level time, and the first holding time is the sum of the exposure time and the second duration time.

[0135] S530, calculating the lighting high level time according to the holding time of the high level state and the shortest switching time.

[0136] S540, calculating the lighting low level time according to the lighting high level time and the inductive duty cycle.

[0137] When the inductive duty cycle is greater than the preset value and a strobe signal is received during the idle low level time, the second duration is recorded. At this time, the idle high level time is the shortest switching time. In the current idle cycle, the PWM signal has passed the sum of the shortest switching time and the second duration. The lighting cycle is composed of two idle cycles, any of which is less than the combined lighting cycle. If the lighting frequency of the combined lighting cycle is not less than the inductive frequency, the idle frequency of any idle cycle within the lighting cycle is not less than the inductive frequency.

[0138] When the second duration is not greater than the shortest switching time, the PWM signal is controlled to maintain a low level state for a maintenance time of Tswitch-Tlow_low, that is, the low level time of the first idle period in the lighting cycle is Tlow_low+Tswitch-Tlow_low=Tswitch. Then, the PWM signal is pulled up to a high level state (equivalent to a high level in the second idle period in the lighting cycle), and the maintenance time is max[Tswitch+Texp-(Tswitch-Tlow_low), Tswitch] (that is, the maintenance time in the high level state is the maximum value between the first maintenance time and the idle high level time), and the lighting high level time is calculated according to the maintenance time of the high level state and the shortest switching time (equivalent to calculating the lighting high level time according to the maintenance time of the high level state and the idle high level time), and the formula is as follows:

[0139]

[0140] Next, pull the PWM signal down to a low level state (equivalent to the low level in the second idle cycle in the lighting cycle), and maintain it for a time of Toff_light-Tswitch, plus the low level time Tswitch in the first idle cycle in the lighting cycle, that is, the low level time of this lighting cycle is Toff_light. The lighting low level time is calculated based on the lighting high level time and the insensitive duty cycle, and the formula is as follows:

[0141]

[0142]

[0143] The lighting duty cycle Dlight is equal to the inductive duty cycle Dacpt, and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an inductive periodic PWM signal.

[0144] In some embodiments of the present application, the relative size between the first holding time and the idle high level time in step S520 is different, and the lighting high level time finally calculated is also different. For example, when the first holding time is not less than the idle high level time, the lighting high level time is the sum of the shortest switching time and the first holding time, and the formula is as follows:

[0145]

[0146] The lighting high-level time is less than or equal to the insensitive high-level time, so the lighting frequency must be greater than or equal to the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0147]

[0148]

[0149] Therefore, Toff_light ≥ 2*Toff_idle ≥ 2*Tswitch, Toff_light-Tswitch ≥ Tswitch, and the lighting high level time and the lighting low level time are not less than the shortest switching time.

[0150] When the first hold time is less than the idle high level time, the lighting high level time is the sum of the shortest switching time and the idle high level time, and the formula is as follows:

[0151]

[0152] The lighting high-level time is less than or equal to the insensitive high-level time, so the lighting frequency must be greater than or equal to the insensitive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0153]

[0154]

[0155] Therefore, Toff_ligh=2*Toff_idle, Toff_light-Tswitch=Toff_idle+(Toff_idle-Tswitch)≥Tswitch, then the lighting high level time and the lighting low level time are not less than the shortest switching time.

[0156] Therefore, when the lighting frequency, lighting duty cycle, lighting high level time and lighting low level time all meet the requirements, after the PWM signal enters the lighting cycle, it can control the LED light source to remain always on during the lighting high level time, thereby providing lighting for the exposure process of the camera's photosensitive chip.

[0157] Reference Figure 6 , which shows a flow chart of determining the lighting cycle of a PWM signal provided by an embodiment of the present application. Figure 6 As shown, including:

[0158] S600, when the second duration is greater than the shortest switching time, the PWM signal is controlled to enter a high level in the next idle period, and the high level holding time in the next idle period is the sum of the exposure time and the shortest switching time.

[0159] S610, calculating the illumination high level time according to the sum of the exposure time, the shortest switching time, and the idle high level time.

[0160] S620, calculating the lighting low level time according to the second duration and the inductive duty cycle.

[0161] When the second duration is greater than the shortest switching time, the PWM signal is pulled high to a high level state (equivalent to the high level of the second idle cycle in the lighting cycle), and the maintenance time is Texp+Tswitch. Adding the idle high level time Ton_idle of the first idle cycle in the lighting cycle, the lighting high level time is obtained, and the formula is as follows:

[0162]

[0163] Next, pull the PWM signal down to a low level state (equivalent to the low level of the second idle cycle in the lighting cycle), and maintain it for a time of Toff_light-Tlow_low. Add the idle low level time Tlow_low of the first idle cycle in the lighting cycle to get the lighting low level time Toff_light. Among them, the lighting duty cycle is equal to the insensitive duty cycle, so the lighting low level time is equal to the insensitive low level time, that is, .

[0164] The lighting duty cycle is equal to the inductive duty cycle, and the brightness of the LED light source perceived by the human eye is consistent with that when the LED light source is controlled by an inductive periodic PWM signal. The lighting high-level time is equal to the inductive high-level time, and the lighting low-level time is equal to the inductive low-level time, so the lighting frequency is equal to the inductive frequency, and the flickering degree of the LED light source is also acceptable to the human eye.

[0165] because:

[0166]

[0167] so:

[0168]

[0169] and:

[0170]

[0171] but:

[0172]

[0173] The lighting high level time and lighting low level time are not less than the shortest switching time. Therefore, when the lighting frequency, lighting duty cycle, lighting high level time and lighting low level time all meet the requirements, after the PWM signal enters the lighting cycle, it can control the LED light source to remain always on during the lighting high level time, providing lighting for the exposure process of the camera's photosensitive chip.

[0174] When receiving a stroboscopic signal under different circumstances, the embodiment of the present application can determine the lighting cycle of the corresponding PWM signal and calculate the high level time and low level time of the lighting cycle, thereby improving the compatibility of the present application and user experience.

[0175] The LED light source control method based on PWM signal proposed in the present application can be applied to a light source control module. The light source control module can be operated independently outside the industrial camera or integrated inside the industrial camera for operation.

[0176] Taking the example of the light source control module running independently outside the industrial camera, the light source control module is integrated into a separate entity outside the industrial camera. For example, it includes but is not limited to a machine vision light source controller. The machine vision light source controller is connected to the LED light source to directly control the on and off, current, etc. of the LED light source; at the same time, the light source controller is connected to the industrial camera to receive the stroboscopic signal sent by the industrial camera. The working process is that after the industrial camera receives the external trigger signal (or photo signal) given by the external sensor, it outputs an exposure signal to the photosensitive chip to start the exposure of the photosensitive chip, and at the same time outputs a stroboscopic signal to the light source control module of the machine vision light source controller, so that it controls the LED light source to provide lighting during the exposure of the photosensitive chip.

[0177] Taking the light source control module integrated inside the industrial camera as an example, the industrial camera is directly connected to the LED light source to control the on and off of the LED light source, current, etc. After receiving the external trigger signal (or photo signal) from the external sensor, the industrial camera outputs an exposure signal to the photosensitive chip to start the exposure of the photosensitive chip, and at the same time outputs a strobe signal to the internal light source control module to control the LED light source to provide lighting during the exposure of the photosensitive chip.

[0178] It should be noted that the above embodiments can be freely combined as needed. The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A light source control method, which controls the light source to provide illumination when the camera is exposed by a PWM signal, characterized in that: include: Acquiring the exposure time of the camera and the shortest switching time of the light source, and receiving a stroboscopic signal sent by the camera, wherein when the stroboscopic signal is not received, the period of the PWM signal is an idle period, and the light source controlled by the PWM signal is used to prevent the human eye from feeling the flicker of the light source during the idle period, and the shortest switching time is the time for the light source to switch between the two states of lighting and extinguishing; Determine an illumination cycle of the PWM signal according to the stroboscopic signal, the exposure time, and the shortest switching time, and calculate an illumination high level time and an illumination low level time of the PWM signal within the illumination cycle, wherein the time when the PWM signal enters the illumination cycle is synchronized with the time when the camera starts exposure, the illumination high level time is greater than the exposure time, and the illumination duty cycle of the illumination cycle is equal to the idle duty cycle of the idle cycle; Calculate the lighting frequency of the PWM signal within the lighting cycle according to the lighting high level time and the lighting low level time; When the lighting frequency is not less than the idle frequency of the PWM signal in the idle period, and both the high level time and the low level time are not less than the shortest switching time, the light source is controlled to remain always on during the lighting high level time to provide lighting for the camera.

2. The light source control method according to claim 1, characterized in that: Also includes: When the duty cycle of the PWM signal is not greater than a preset value, the high level time of the PWM signal is kept unchanged, and the low level time of the PWM signal is continuously reduced until the human eye cannot perceive the flicker of the light source; When the duty cycle of the PWM signal is greater than the preset value, the low level time of the PWM signal is kept unchanged, and the high level time of the PWM signal is continuously increased until the human eye cannot perceive the flicker of the light source; Using the PWM signal after the high level time or the low level time is adjusted as a non-inductive periodic PWM signal; Calculate the idle high level time and the idle low level time according to the inductive duty cycle of the inductive periodic PWM signal and the shortest switching time; When the stroboscopic signal is not received, the light source is controlled to be on and off by the idle high level time and the idle low level time of the PWM signal in the idle period, wherein the idle duty cycle is equal to the inductive duty cycle, the idle frequency is not less than the inductive frequency of the inductive period PWM signal, and the idle high level time and the idle low level time are not less than the shortest switching time.

3. The light source control method according to claim 2, characterized in that: The step of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time and the shortest switching time, and calculating the lighting high level time and the lighting low level time of the PWM signal within the lighting cycle, specifically includes: When the stroboscopic signal is received within the idle high level time, the current idle period is used as the lighting period, and the first duration of the PWM signal within the idle high level time is recorded; Determine whether the sum of the first duration, the exposure time and the shortest switching time is greater than the idle high level time; If not, calculating the lighting high level time according to the first duration and the idle high level time, and calculating the lighting low level time according to the insensitive duty cycle and the lighting high level time; If it is greater, the illumination high level time is calculated according to the exposure time, the shortest switching time and the first duration, and the illumination low level time is calculated according to the inductive duty cycle and the illumination high level time.

4. The light source control method according to claim 2, characterized in that: The step of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time and the shortest switching time, and calculating the lighting high level time and the lighting low level time of the PWM signal within the lighting cycle, specifically includes: When the inductive duty cycle is greater than the preset value and the stroboscopic signal is received within the idle low level time, the next idle cycle of the current idle cycle is used as the lighting cycle, and the second duration of the PWM signal within the idle low level time of the current idle cycle is recorded; Determine whether the sum of the second duration and the exposure time is greater than the idle high level time; If not, the idle high level time is used as the lighting high level time, and the idle low level time is used as the lighting low level time.

5. The light source control method according to claim 4, characterized in that: Also includes: If the sum of the second duration and the exposure time is greater than the idle high level time, calculating the illumination high level time according to the exposure time and the second duration; The lighting low level time is calculated according to the lighting high level time and the inductive duty cycle.

6. The light source control method according to claim 2, characterized in that: The step of determining the lighting cycle of the PWM signal according to the stroboscopic signal, the exposure time and the shortest switching time, and calculating the lighting high level time and the lighting low level time of the PWM signal within the lighting cycle, specifically includes: When the inductive duty cycle is not greater than the preset value and the stroboscopic signal is received within the idle low level time, the current idle cycle and the next idle cycle are used as the lighting cycle, and the second duration of the PWM signal within the idle low level time of the current idle cycle is recorded; When the second duration is not greater than the shortest switching time, controlling the PWM signal to maintain a low level state in the current idle period, and the maintenance time is the shortest switching time minus the second duration; After the low level state ends, the PWM signal is pulled up to a high level state in the next idle period, and the holding time of the high level state is the maximum value between the first holding time and the idle high level time, and the first holding time is the sum of the exposure time and the second duration; Calculate the lighting high level time according to the holding time of the high level state and the shortest switching time; The lighting low level time is calculated according to the lighting high level time and the inductive duty cycle.

7. The light source control method according to claim 6, characterized in that: Also includes: When the first holding time is not less than the idle high level time, calculating the lighting high level time according to the first holding time and the shortest switching time; When the first holding time is shorter than the idle high level time, the lighting high level time is calculated according to the idle high level time and the shortest switching time.

8. The light source control method according to claim 6, characterized in that: Also includes: When the second duration is greater than the shortest switching time, controlling the PWM signal to enter a high level in the next idle period, and maintaining the high level in the next idle period for a time equal to the sum of the exposure time and the shortest switching time; Calculate the illumination high level time according to the sum of the exposure time and the shortest switching time and the idle high level time; The lighting low level time is calculated according to the second duration and the inductive duty cycle.

9. A machine vision light source controller, characterized in that: Used to control the on and off of a light source through the light source control method described in any one of claims 1 to 8.

10. An industrial camera, characterized in that: Used to control the on and off of a light source through the light source control method described in any one of claims 1 to 8.

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