JPH02165880A - laser marker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a one-shot laser marker using a pulsed laser, and particularly to a laser marker using a transmission type liquid crystal cell as a masking means.

[Conventional technology]

As a means to prevent contrast fluctuations due to environmental changes in the temperature at which the liquid crystal cell is used, in commercially available liquid crystal displays, a thermistor is installed on the circuit board on which the liquid crystal cell is mounted, and the liquid crystal display drive voltage is automatically adjusted by changing the resistance of the thermistor. Measures for adjustment are widely implemented.

[Problem to be solved by the invention]

The above-mentioned conventional technology was designed for a state in which the liquid crystal cell and the drive circuit system are at approximately the same ambient temperature, and the display can generally be sufficiently controlled.

However, in the method of using a liquid crystal cell as a masking means, a temperature difference of 10 to 30 degrees Celsius occurs between the inside of the liquid crystal cell and the drive circuit system depending on the conditions of the irradiated laser, so the conventional technology cannot be applied, and the controller ~Causes unevenness at the end.

In addition, when considering high-mix, low-volume production, it is necessary to optimize each liquid crystal cell drive system when determining laser conditions, which poses a problem in that it takes time.

An object of the present invention is to provide a laser marker that can be clearly marked regardless of laser irradiation conditions.

[Means to solve the problem]

The above object is achieved by predicting the temperature inside the liquid crystal cell in advance based on laser irradiation conditions and setting the optimum liquid crystal cell drive voltage for this predicted temperature.

[Effect]

The temperature that the liquid crystal may experience during marking is estimated in advance from the laser irradiation conditions such as the area of laser irradiation on the liquid crystal cell, the irradiation laser energy, and the number of laser repetitions, and the liquid crystal temperature of the laser irradiation surface. On the other hand, the dynamic characteristics with respect to the liquid crystal temperature are recorded as a database in the control system, and the optimum operating point (driving voltage) at the previous liquid crystal temperature is set.

As a result, it is possible to perform marking with a constant contrast without being affected by changes in liquid crystal temperature based on laser irradiation conditions.6 [Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1. - is a pulsed laser having an oscillation wavelength in the wavelength range from visible to near infrared, and is typically represented by a YAG laser. A linearly polarized laser beam 2 (here, P-polarized light) emitted from a pulse laser 1 passes through a beam expansion/shaping section 3.
The liquid crystal cell 4 is irradiated with light. The liquid crystal cell 4 includes a liquid crystal drive system 5,
It is operated by the liquid crystal control system 6, and depending on the energy of the laser beam 2, the cooling device 4i is used to release heat generated during laser irradiation!
(not shown) is provided.

The laser beam 7 that has passed through the liquid crystal cell 4 is separated by a beam splitter 8 into a P-polarized laser beam 9 reflecting pattern information for marking and a pattern light 10 for non-marking. Of these, the P-polarized laser beam 9 is imaged on the surface to be processed 12 by the condenser lens optical system 11, and the non-engraving pattern beam 10
is absorbed by the absorber 13.

The pulse laser 1 is operated by a power supply system 14 and a control system 15, and the liquid crystal control system 6 and the laser control system 15 are controlled by a central control system 16. Connected to the central control system 16 is a database 17 regarding liquid crystal cell drive characteristics with respect to laser irradiation conditions for the liquid crystal cell 4 .

The operation will be explained below using FIGS. 2 to 6. FIG. 2 shows how the liquid crystal temperature changes when the liquid crystal cell is irradiated with a pulsed laser. The horizontal axis is time t, and the vertical axis is temperature T.

Laser irradiation starts at time t1, and the temperature of the liquid crystal rises rapidly during pulsed laser irradiation, cools down during the pulse rest period, and then rises rapidly again during the next pulsed irradiation. The temperature is gradually approaching the saturation temperature T1.

The saturation temperature T1 is determined by the laser energy density of one pulse (J/a
The laser loss inside the liquid crystal cell is divided into Tp which depends on J), T which depends on the average output density (W/d) determined from the laser energy density and pulse repetition rate, and the reference temperature To before laser irradiation. This is a characteristic found through analysis.

On the other hand, the electro-optical characteristics and contrast ratio of liquid crystal will be explained using FIG. 3. The horizontal axis in the figure shows the driving voltage V, and the vertical axis shows the transmittance P of the liquid crystal cell.

Characteristic I is the characteristic of the pattern-formed area, and characteristic (2) is the characteristic of the pattern-free area. The contrast ratio with such characteristics is generally expressed as the ratio of the transmittance of the patterned part to the transmittance of the non-patterned part at the driving voltage, for example, vl.

It is well known that, as a physical property of liquid crystals, the elastic constant decreases as the temperature increases, and the transmittance for the same driving voltage increases. According to the above, characteristic I in FIG. 3 is said to shift to the left side as shown in FIG. 4 as the temperature rises. Similar to the characteristic (2), the characteristic (not shown) also shifts to the left, so if the liquid crystal temperature increases while the driving voltage (2) is kept constant, the contrast ratio decreases.

FIG. 5 shows the relationship between temperature and contrast ratio.

The horizontal axis is the temperature T, and the vertical axis is the contrast ratio.

Similarly, when the voltage changes to Tel Ta and T4, if we calculate the voltage that maximizes the contrast ratio K, we find that the voltage must be lowered to V Z TV a * V 4 respectively. .

Optimal drive voltage change ΔV/ΔT for liquid crystal temperature change ΔT
Although it depends on the liquid crystal material, the voltage effective value display is -6 to -15 m.
V/deg. Considering the practical conditions as a liquid crystal cell, in the case of 1/64 duty drive,
The voltage change rate is -40 to -102m when the driving voltage is 14V.
It becomes V/deg. Therefore, if a temperature change of 3Qdeg occurs, the dynamic voltage of -1, 2 to -3Vll must be adjusted.

Once the liquid crystal material used for the liquid crystal cell 4 is selected, its ΔV
/ΔT is determined, and thereby the characteristics shown in FIG. 6 are obtained. By recording the optimum drive voltage characteristics with respect to the liquid crystal temperature and the temperature characteristics shown in FIG. 2 in the database 17, the central control system 16 issues a drive voltage setting command to the liquid crystal control system 6 according to each laser irradiation condition. ,constantly,
It can be controlled to a state where a high contrast ratio can be obtained. Thereafter, a laser oscillation command is issued to the laser control system 15, and marking is performed.

According to this embodiment, no matter how the laser irradiation conditions change, the liquid crystal temperature rise during laser irradiation can be predicted and the liquid crystal cell drive voltage can be optimized.

In the above embodiment, the temperature rise characteristics themselves during laser irradiation are recorded in the database 17, but according to the instructed laser irradiation conditions, calculations are performed within the central control system 16 to determine the temperature rise characteristics, and the temperature rise characteristics are recorded in the database 17. From the temperature-driving voltage characteristics of

Even if the sequence is used to find the optimum drive voltage, the effect remains the same.

Further, according to the embodiment, when setting the laser irradiation conditions for the workpiece, the settings of the liquid crystal cell drive system are automatically optimized for the laser irradiation conditions, so the time for setting the laser conditions can be significantly shortened. Can be done.

[Effects of the Invention] According to the present invention, the liquid crystal driving voltage can be constantly optimized and controlled in response to the temperature rise of the liquid crystal, so a constant contrast ratio can be obtained regardless of the laser irradiation conditions, and the marking quality can be stabilized. There is an effect.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a temperature rise characteristic diagram, Figure 3 is an electro-optical characteristic diagram, Figure 4 is a temperature change diagram of electro-optical characteristics, and Figure 5 is a contrast ratio diagram. FIG. 6 is a temperature-contrast ratio-voltage characteristic diagram. DESCRIPTION OF SYMBOLS 1... Pulse laser, 4... Liquid crystal cell, 5... Liquid crystal drive system, 6... Liquid crystal control system, 15... Laser control system, 16... Central control system, 17... database. Fast-talking m- and t

Claims (1)

[Claims] 1. A transmissive liquid crystal cell to which pattern information of a mark to be engraved is given from the outside, and a linearly polarized laser beam emitted from a laser light source over a wavelength range from visible wavelengths to near-infrared wavelengths. In a laser marker including a means for irradiating the transmissive liquid crystal cell and an optical system that images the laser beam transmitted through the transmissive liquid crystal cell on a surface to be processed, the driving voltage of the transmissive liquid crystal cell is set to A laser marker characterized by being provided with a means for optimization control based on laser irradiation conditions. 2. In claim 1, the driving voltage of the transmissive liquid crystal cell is optimized by using at least the laser irradiation area, irradiation laser energy, and laser repetition rate on the transmissive liquid crystal cell as the laser irradiation conditions. A laser marker characterized by control. 3. The driving voltage optimization control according to claim 1 or 2 predicts the liquid crystal temperature in the transmissive liquid crystal cell according to the laser irradiation conditions, and adjusts the dynamic characteristics based on the liquid crystal temperature change. A laser marker characterized in that the laser marker is set by following changes and setting a drive voltage of the transmissive liquid crystal cell.