JP4633681B2 - Light irradiation system and light control device - Google Patents

Description

  The present invention relates to a light irradiation system for irradiating a target such as a product with a light emitting diode (hereinafter also referred to as “LED”) and a light control device for dimming the LED.

  Conventionally, PWM control is known as a dimming (brightness control) method for LEDs in addition to continuous current control (Patent Document 1).

  In addition, in order to perform more precise brightness control, a combination type system in which the current during the ON period (High period) is controlled at a constant current while being based on PWM control has recently been developed.

However, when the LED is dimmed by the PWM control method, the brightness of the LED at a low duty ratio when the repetition fundamental frequency (resolution) is increased is not proportional to the duty ratio. This is due to the fact that the rise L of the LED emission cannot catch up with the pulse width W of the control current ON period, which is the input signal, as shown in FIG. In particular, in the combination method, since feedback control is performed, it takes a long time to rise, and this phenomenon becomes remarkable. As a result, for example, in imaging at a high shutter speed, there is a problem that desired light control cannot be performed with the control method.
JP 2001-153808 A

  Therefore, the present invention has been made to solve these problems. Even when the pulse width of the ON period is set to be extremely short by accelerating the rise of the LED, the pulse width or the duty is set. The main aim of the present invention is to provide a light irradiation system and a light control device that can adjust the brightness to a desired brightness based on the ratio and can be suitably used for imaging at a high shutter speed.

In the present invention, the light irradiation system includes an LED that emits light to an object,
A drive unit that dims the LED by providing an ON period and an OFF period for the LED, and supplies an operating current during the ON period based on an operating current instruction value. And a drive unit that supplies a standby current smaller than the operating current in a predetermined period before the rising of the ON period in the OFF period based on a standby current instruction value.

  In such a light irradiation system, since the standby current is positively biased with respect to the LED during a predetermined period before the ON period rises, the slope of the LED rise is larger than when the LED is started from zero. In addition, the rise of the LED can be speeded up. Therefore, even when the LED is started up with a margin within the pulse width of the ON period and the ON period is finely set to be extremely short, the LED can be dimmed to a desired brightness based on the pulse width or the duty ratio, and fast. It is possible to obtain a light irradiation system that can be suitably used for imaging at the shutter speed.

  The standby current instruction value is at least 0 <standby current instruction value <operating current instruction value, and is preferably set to a value near the lower limit of the non-saturated region of the LED. The standby current may be supplied over the OFF period, but before the ON period rises for a predetermined time, the rising characteristic of the ON period is substantially the same as when the standby current is supplied over the OFF period. It is sufficient to supply at least a standby current. Further, the value of the standby current may be set so that the LED does not emit light by visual observation, or may be set so that the LED shines slightly dimly. If it is dimly lit, there is also an advantage that a failure can be detected quickly.

  In addition, a drive unit for dimming the LED by supplying an electric current by providing an ON period and an OFF period to an LED that irradiates light on an object, and the ON part based on an operating current indication value A light control device comprising a drive unit that supplies an operating current during a period and supplies a standby current smaller than the operating current in a predetermined period before the rising of the ON period in the OFF period based on a standby current instruction value If it is (Claim 2), the light control of LED similar to the case of the light irradiation system mentioned above is realizable.

  More preferably, the operating current instruction value, the standby current instruction value, and an ON / OFF signal for setting the ON period and the OFF period are input, and the standby current instruction value is set over the OFF period, It is preferable to further include a binary signal output unit that sets the operating current instruction value over the ON period.

  Further, the present invention further includes a feedback control unit that detects a current flowing through the light emitting diode at least in the ON period and controls the detected current value to approach the operating current instruction value (Claim 3). The effect of the invention is particularly remarkable. That is, with such a current feedback control configuration, conventionally, the delay of the rise of the LED has become a bottleneck, and it is not possible to take full advantage of the feature of this method that enables accurate light quantity and wavelength control during the ON period. However, according to the present invention, the rise of the LED can be speeded up by the bias of the standby current, so that the light that is very high quality and can be used for various purposes is combined with the accurate light amount and wavelength control during the ON period. An irradiation system or the like can be provided.

  As a specific embodiment of the feedback control unit, a detection unit that detects the operation current and the standby current supplied to the light emitting diode and outputs a detection current value, and a detection current value that is the operation current instruction value and the detection current value. It can be mentioned that it is composed of a correction unit that outputs a control signal of a value corresponding to the difference to the standby current instruction value to the drive unit (Claim 5).

  The ON period and the OFF period are set based on a PWM signal having a predetermined frequency at which the ON period and the OFF period are switched within one cycle, and the drive unit determines the LED according to a ratio between the ON period and the OFF period. Even in the case of a low duty ratio when the repetition fundamental frequency is set high and finely by offsetting and supplying the standby current to the LED, The brightness control of the LED can be reliably performed based on the duty ratio. Therefore, even when imaging is performed at a high shutter speed, it is possible to perform dimming of the LED by fine-tuned PWM control sufficiently corresponding thereto.

  Even if the drive unit provides the ON period and the OFF period to flash the LED (Claim 7), it is possible to speed up the rise of the LED by offsetting the standby current. it can. Therefore, even when it is necessary to set the flash emission period to be extremely short in order to cope with imaging with a high shutter speed, it is possible to realize flash emission sufficiently corresponding thereto.

  In the case where the LED is an LED group in which a plurality of LEDs arranged close to each other are connected in electrical series, and the LED group is further connected in electrical parallel, a standby current is applied to the LED group. Even if there is a defect or failure in one LED, it is possible to check the operating status of the entire group connected in series, so that the operating status of the LED Can be easily determined.

  Thus, according to the present invention, the stand-by current is biased with respect to the LED for a predetermined period before the rise of the ON period, so that the rise of the LED can be speeded up. Therefore, the LED can be started up with a margin within the pulse width of the ON period. Therefore, even when the ON period is finely set to be extremely short, the light irradiation system can be adjusted to a desired brightness based on the duty ratio and can be suitably used for imaging at a high shutter speed. Alternatively, a light control device can be provided.

  Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

  FIG. 1 is a schematic diagram showing an entire light irradiation system 100 according to the present embodiment. The light irradiation system 100 is used for surface inspection of a product or the like (also referred to as a workpiece), and includes a lighting device 1, a power source 2 connected to the lighting device 1 by an electric cable 4, and the power source 2. For example, a light control device 3 housed in the same housing is provided.

  As shown in FIGS. 1 to 3, the illumination device 1 is, for example, a disk-shaped device whose bottom surface emits light, and in order to inspect the surface of a workpiece and detect a mark, the bottom surface of the illumination device 1 is brought close to the workpiece. Illuminate. An observation hole H is penetrated in the center of the illumination device 1, and imaging or visual observation of the work surface illuminated through the observation hole H can be performed.

  A large number of LEDs 11 are laid concentrically on the bottom surface of the lighting device 1 for the above-described surface emission. As shown in FIG. 4, a plurality of LEDs 11 are connected in series to form an LED series circuit, and a plurality of LED series circuits are connected in parallel. In order to supply power to the LEDs 11, a connection terminal including a plus terminal 12 and a minus terminal 13 is provided, and the electric cable 4 is connected thereto.

  The power source 2 is constituted by a constant voltage direct current type that supplies a constant voltage to the LED 11, and the constant voltage line is connected to the plus terminal 12 of the lighting device 1 via the electric cable 4.

  The light control device 3 is a digital / analog hybrid circuit composed of a CPU or discrete components, and mainly includes a binary signal output unit 31 and a constant current control unit 32 as shown in the functional block diagram of FIG. Yes.

  Each of these parts will be described with reference to FIG.

  The binary signal output unit 31 receives an operating current instruction value, a standby current instruction value, a PWM (Pulse Width Modulator) signal for setting an ON period and an OFF period, and based on these input signals, indicates a standby current instruction during the OFF period. A value is set, and an operating current instruction value is set during the ON period.

  More specifically, the binary signal output unit 31 receives a PWM signal (see FIG. 6) having a predetermined frequency that switches between an ON signal period and an OFF signal period in one cycle from a PWM controller (not shown). The The switching frequency of the PWM signal in this embodiment is, for example, several tens of kHz, one cycle is several to several tens of μs, and 256-level dimming is possible. That is, the shortest period of the pulse width of the ON signal is on the order of several tens to several hundreds ns. Further, a current instruction signal having two values (voltage values), that is, an operating current instruction value and a standby current instruction value, is input to the binary signal output unit 31 from a current instruction circuit (not shown).

  Then, a binary signal having a voltage value of the standby current instruction value during the OFF period of the PWM signal and a voltage value of the operating current instruction value during the ON period is output to the constant current control unit 32.

  Note that the standby current instruction value is set so that at least 0 <standby current instruction value <operating current instruction value, and in this embodiment, a current value (standby current value) passed through the LED 11 in accordance with the standby current instruction value Is set to a value near the lower limit of the non-saturated region. In other words, the standby current value is a current value at which the LED 11 is not visually recognized to emit light, or is slightly dimmed and can be recognized. If it is dimly lit, there is also an advantage that a failure can be detected quickly.

  The constant current control unit 32 compares the detection current value detected by the detection unit 323 that detects an actual current flowing through the LED 11 with the operation current instruction value and the standby current instruction value, and determines the difference between them. A correction unit 321 that outputs a control signal having a value corresponding thereto, supplies an operating current during the ON period, and supplies a standby current during the OFF period to supply power to the LED 11 by providing an ON period and an OFF period. And a driving unit 322 for performing the above operation.

  The detection unit 323 includes a detection circuit including a current detection resistor electrically connected in series with the driving unit 322, and measures a voltage value between terminals of the current detection resistor and amplifies the voltage value. For example, a detection signal is generated and output to the correction unit 321.

  The correction unit 321 receives the value of the binary signal (operation current instruction value and standby current instruction value) output from the binary signal output unit 31 and the detection current value output from the detection unit 323, These are compared, and a control signal having a value corresponding to the difference is output to the drive unit 322, and is constituted by a comparison amplifier circuit including an operational amplifier. The detection unit 323 and the correction unit 321 constitute a feedback control unit described in the claims.

  The drive unit 322 is mainly composed of an amplifier circuit such as an FET or a transistor, and is connected in series downstream of the LED 11. Then, a current corresponding to the value of the control signal is supplied to the LED 11. That is, the operating current is supplied during the ON period based on the operating current instruction value, and at least a predetermined period before the rise of the ON period in the OFF period based on the standby current instruction value (in this embodiment, a period equal to the OFF period) ) Is supplied with standby current.

  The operation of the light irradiation system according to the present embodiment configured as described above will be described mainly with reference to FIGS.

  First, the binary signal output unit 31 outputs a binary signal (an operating current instruction value as a high level and a standby current instruction value as a low level) synchronized with the PWM signal. On the other hand, the current value actually flowing through the LED 11 is measured and output from the detection unit 323.

  Then, the correction unit 321 compares the operating current instruction value and the standby current instruction value with the detected current value actually flowing through the LED 11, and outputs a control signal having the difference value to the driving unit 322.

  The drive unit 322 amplifies the value of the control signal and drives the LED with the value.

  In this way, current feedback control is performed on the LED 11 targeting the value of the binary signal output from the binary signal output unit 31, and as a result, the LED 11 has one cycle as shown in FIG. Thus, a current (operating current and standby current) for switching between the High level period (ON period) and the Low level period (OFF period) is supplied.

  At this time, since the driving unit 322 actively offsets the standby current and supplies the LED 11 to the LED 11 in the OFF period, the slope of the rising of the LED 11 in the ON period becomes large as shown in FIG. It rises quickly with a margin within the pulse width W of the ON period.

  That is, according to this light irradiation system, the light emission rise time of the LED 11 at the time of ON can be greatly improved as compared with the prior art. Therefore, even if the PWM control frequency is set faster than the prior art, the light quantity proportional to the duty ratio Adjustments can be made. In addition, as a result of speeding up the frequency of PWM control, its application can be greatly expanded compared to the prior art, such as imaging with a faster shutter speed.

  In particular, in this embodiment, since the delay of the light emission rise time, which is a drawback of the feedback current control, can be eliminated, the advantage of the feedback current control, that is, the desired brightness controlled reliably without depending on the individual characteristics of the LED can be maintained. Taking advantage of both the advantages of PWM control, that is, the ability to provide high-quality light without wavelength fluctuations even when dimming, this light irradiation system should be applied to fields that were not conceived in the past. Is possible.

  Further, in the light irradiation system composed of a large number of LEDs 11 as in the present embodiment, if the standby current is applied as described above and the LEDs 11 are allowed to emit light thinly, it is visually observed prior to actual operation. The status of the LED 11 can be confirmed, and the failure or the like can be easily determined.

  The present invention is not limited to the above embodiment. For example, the drive unit 322 supplies standby current to the LEDs over the OFF period, but the standby current is supplied at least in a predetermined period before the rising of the ON period in the OFF period based on the standby current instruction value. Any supply is acceptable.

  Further, in the case where the light emission is pulsed once to several times irregularly, that is, in the form of flash light emission, the ON period (flash light emission period) and the OFF period are switched within one cycle instead of the PWM signal. A flash light emission drive signal having a frequency can be input. Even in this case, the rising of the LED can be speeded up by positively offsetting the above-described standby current in a predetermined period before the rising of the flash emission period. Thereby, even when the flash emission period has to be set to be extremely short in order to cope with imaging with a high shutter speed, it is possible to realize flash emission adjusted based on the pulse width. In addition, in the case of the flash emission type, it is often difficult to confirm the operation status of the LED. However, as described above, the operation status of the LED can be confirmed by positively offsetting the standby current. The advantage of being easy becomes remarkable.

  Furthermore, although the example which performs the current control by feedback was given in the said embodiment, you may control an electric current value by an open loop. In addition, a configuration in which open loop control is performed only during an OFF period, and a configuration in which open loop control is performed only during an ON period are also conceivable.

  In addition, the drive unit may be disposed on the lighting device side. Faster control is possible because the stray capacitance due to the cable is reduced.

  Moreover, in a line light illumination system in which power-type LEDs are arranged in a row, scanning on the image device side is fast, so conventional PWM control cannot follow, and dimming is performed by continuous current control. In particular, when used in a low current region, since only a very low voltage acts on each LED, a non-lighting appears due to the difference in Vf of each LED, causing a noticeable variation in brightness and darkness. There was a big problem that the linearity in light deteriorated.

  However, according to this embodiment, as a result of speeding up, PWM control can be used even in such a case, so that the brightness of each LED can be balanced to a very small amount of light, and the linearity can be reliably adjusted. Can be light.

  Furthermore, when the power LED is controlled with a continuous current, the color shifts in a low current region or the like. However, PWM control can suppress the phenomenon and improve the light quality.

  In addition to the above description, the present invention can be implemented with appropriate modifications without departing from the spirit of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The whole schematic block diagram which shows one Embodiment of the light irradiation system concerning this invention. The top view of the light control apparatus in the embodiment. The longitudinal cross-sectional view of the light control apparatus in the embodiment. The schematic circuit diagram of the light irradiation apparatus in the embodiment. The functional block diagram of the light irradiation system in the embodiment. The figure which shows the ON period and OFF period in the embodiment. The figure which shows operation | movement of the light irradiation system and light control apparatus in the embodiment. The figure which shows the prior art of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Illumination device 11 ... Light emitting diode (LED)
2 ... Power supply 3 ... Light control device 31 ... Binary signal output unit 32 ... Constant current control unit 321 ... Correction unit 322 ... Drive unit 323 ... Detection unit 4・ Electric cable W ・ ・ ・ Input pulse width L ・ ・ ・ Rise of light quantity of light emitting diode (LED)

Claims (8)

A light emitting diode that irradiates the object with light;
A drive unit that dims the light emitting diode by supplying an ON period and an OFF period to the light emitting diode, and supplies an operating current during the ON period based on an operating current instruction value together, supplying at least the rather smaller than the operating current to a predetermined period before the rise of the oN period and the standby current of the extent to the light emitting diode shines size human recognizable in the OFF period based on the standby current instruction value A drive unit to
A light irradiation system comprising: A drive unit for dimming the light emitting diode by supplying an electric current by providing an ON period and an OFF period to the light emitting diode that irradiates light to the object, and the ON part based on an operating current indication value supplies the operating current to the period, the light emitting diode shines extent at least the rather smaller than the operating current to a predetermined period before the rise of the oN period, and human-perceivable in the OFF period based on the standby current instruction value A light control device including a driving unit that supplies a standby current having a magnitude . The operating current instruction value, the standby current instruction value, and an ON / OFF signal for setting the ON period and the OFF period are input, the standby current instruction value is set over the OFF period, and the ON period is set over the ON period. The light control apparatus according to claim 2, further comprising a binary signal output unit that sets the operating current instruction value.   4. The light control device according to claim 2, further comprising a feedback control unit that detects a current flowing through the light emitting diode at least in the ON period and controls the detected current value to approach the operating current instruction value.   The feedback control unit detects the operating current and the standby current supplied to the light emitting diode and outputs a detected current value, and compares the detected current value with the operating current command value and the standby current command value The light control apparatus according to claim 4, further comprising a correction unit that outputs a control signal having a value corresponding to the difference to the drive unit.   The ON period and the OFF period are set based on a PWM signal having a predetermined frequency at which the ON period and the OFF period are switched within one cycle, and the drive unit emits the light emission according to a ratio between the ON period and the OFF period. The light control device according to claim 2, wherein the light control device is for dimming the diode.   The light control device according to claim 2, wherein the driving unit is configured to provide the ON period and the OFF period to cause the light emitting diode to flash.   The light-emitting diode is a light-emitting diode group in which a plurality of light-emitting diodes arranged close to each other are electrically connected in series, and the plurality of light-emitting diode groups are further connected in electrical parallel. The light control device according to any one of 7.