Multi-axis photoelectric sensor

Abstract

This suppresses the response time delay when multiple light curtains are connected in series. [Solution] The multi-axis photoelectric sensor 1 includes a light emission control unit 181 that controls the light emission operation of the light emitters 100(1) and (2) in parallel while shifting the light emission timing of the multiple light emission elements 160 provided on the light emitter 100(1) of the light curtain 1(1) and the light emission timing of the multiple light emission elements 160 provided on the light emitter 100(2) of the light curtain 1(2); a light receiving control unit 281 that controls the light receiving operation of the light receiver 200(1) of the light curtain 1(1) and the light receiver 200(2) of the light curtain 1(2) in accordance with the light emission operation of the light emitters 100(1) and (2); and an output circuit 283 that outputs safety signals OSSD1 and OSSD2 to the outside, which are generated based on whether or not the optical axis Oax formed between the light emitters 100(1) and (2) and the light receivers 200(1) and (2).

Description

Technical Field

[0001] The present invention relates to a multi-axis photoelectric sensor including a plurality of light curtains connected in series.

Background Art

[0002] A light curtain is one aspect of a multi-axis photoelectric sensor. A light curtain detects a person or an object according to whether the optical axes formed between a projector and a light receiver are blocked.

[0003] Conventionally, a form in which a plurality of light curtains are connected in series, so-called cascade connection, is known (see, for example, Patent Document 1). According to cascade connection, the wiring of power cables and input / output cables can be reduced as compared with a form in which a plurality of light curtains are used individually. Note that cascade connection can be used when it is desired to extend the length of the light curtain, or when it is desired to form a protected area in an L shape or a U shape.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above cascade connection, a plurality of light curtains can be installed adjacent to each other. Therefore, it is necessary to prevent optical interference between adjacent light curtains.

[0006] Therefore, in a conventional cascaded connection, the optical axis scan, i.e., the light emission / receiving operation, is performed sequentially starting from the leading optical axis of the first light curtain located at the upstream end, i.e., the side closest to the controller. Once the optical axis scan is completed up to the end optical axis of the first light curtain, the optical axis scan continues sequentially starting from the leading optical axis of the second light curtain. After that, the optical axis scan continues sequentially down to the end optical axis of the light curtain located at the downstream end, i.e., the side furthest from the controller.

[0007] More specifically, the multiple light-emitting elements in each of the multiple light-emitting devices perform light-emitting operations sequentially from the upstream side. Similarly, the multiple light-receiving elements in each of the multiple light-receiving devices perform light-receiving operations sequentially from the upstream side in synchronization with the multiple light-emitting elements. Therefore, light emission and reception operations are performed sequentially, one optical axis at a time, from the leading optical axis of the light curtain located at the upstream side to the trailing optical axis of the light curtain located at the downstream side.

[0008] In short, in conventional cascading connections, multiple light curtains operate in series as a single long light curtain, or a series of light curtains. As a result, optical interference between adjacent light curtains can be prevented.

[0009] However, when multiple light curtains connected in series are operated in series as a series of light curtain groups, the response time from the start to the end of a series of optical axis scans becomes longer. This response time may be understood as the time required from the change in the shading state of each of the multiple optical axes until the logic level of the safety signal switches.

[0010] In particular, the more floodlights connected in series, and consequently the more light-emitting elements there are, the longer the response time will be. A slower response time for the light curtain necessitates a longer safety distance from the machinery to which the light curtain is attached. As a result, the equipment becomes larger, which can be a disadvantage for the user. The safety distance mentioned above must be greater than the minimum distance required for the machinery to stop before a person enters the detection area of ​​the light curtain and reaches the danger zone.

[0011] Furthermore, in a series of light curtain groups, precise timing adjustment is required between multiple light curtains connected in series in order to perform light emission / reception operations one optical axis at a time, from the leading optical axis to the trailing optical axis. Therefore, in conventional cascade connections, communication and synchronization control are performed between multiple light emitters and multiple light receivers, respectively.

[0012] Generally, differential serial communication standards, such as the RS485 standard, can be used as the communication standard between multiple light transmitters and multiple light receivers. However, the RS485 standard requires two communication lines (RS485(+) / RS485(-)). Therefore, the number of wires required for both the light transmitter and the light receiver increases.

[0013] In particular, the receiver is originally connected to a 2-core power line (0V / 24V) and a 2-core signal line (OSSD1 / OSSD2). Therefore, if you want to connect the above 2-core communication line (RS485(+) / RS485(-)), you would need to provide a connector with 6 or more pins on the receiver, making it impossible to use a general-purpose 5-pin M12 connector.

[0014] In view of the above problems, the present invention aims to suppress the delay in response time in a multi-optical-axis photoelectric sensor in which multiple light curtains are connected in series. [Means for solving the problem]

[0015] The multi-optical axis photoelectric sensor according to the present invention includes a plurality of light curtains, each having a light emitter equipped with a plurality of light-emitting elements and a light receiver equipped with a plurality of light-receiving elements that receive light emitted from the plurality of light-emitting elements, and a series of light curtain groups is formed by connecting the light emitters and light receivers in series between one light curtain and another light curtain, wherein the light emission timing of a plurality of first light-emitting elements provided in the first light emitter of one light curtain and a plurality of second light-emitting elements provided in the second light emitter of the other light curtain The system includes: a light emission control unit that controls the light emission operation of the first light emitter and the second light emitter in parallel while staggering the light emission timing; a light receiving control unit that controls the light receiving operation of the first light receiver of one light curtain and the second light receiver of the other light curtain in accordance with the light emission operation of the first light emitter and the second light emitter; and an output circuit that outputs a safety signal to the outside, generated based on whether or not a plurality of optical axes formed between the first light emitter and the first light receiver and between the second light emitter and the second light receiver are in a light-shielding state.

[0016] Further details regarding other features, elements, steps, advantages, and characteristics will become clearer from the embodiments for carrying out the invention and the accompanying drawings. [Effects of the Invention]

[0017] In this invention, adjacent light curtains connected in series operate in parallel with their respective light emission / reception timings staggered. Therefore, delays in response time can be suppressed. [Brief explanation of the drawing]

[0018] [Figure 1] This diagram shows the schematic configuration of a light curtain. [Figure 2] This is a perspective view showing the overall configuration of the floodlight. [Figure 3] This is a front view showing the overall configuration of the floodlight. [Figure 4] This is a perspective view showing one end of a floodlight. [Figure 5] It is a functional block diagram of a light curtain. [Figure 6] It is a diagram showing a first embodiment of a projector. [Figure 7] It is a diagram showing an arrangement example of a light source for an indicator lamp in the first embodiment. [Figure 8] It is a diagram showing the relationship between the emission color and the operation mode. [Figure 9] It is a diagram showing an arrangement example of a light source for an indicator lamp in the second embodiment. [Figure 10] It is a diagram showing an example of a display pattern in the second embodiment. [Figure 11] It is a diagram showing an arrangement example of a light source for an indicator lamp and an example of a display pattern in the third embodiment. [Figure 12] It is a diagram showing an arrangement example of a light source for an indicator lamp and an example of a display pattern in the fourth embodiment. [Figure 13] It is a diagram showing the relationship between the average light reception amount and the display pattern. [Figure 14] It is a diagram showing the relationship between the minimum light reception amount and the display pattern. [Figure 15] It is a diagram showing a lighting image (first example) of a light curtain. [Figure 16] It is a diagram showing a lighting image (second example) of a light curtain. [Figure 17] It is a functional block diagram of a light curtain having a display pattern control function. [Figure 18] It is a diagram showing the processing flow of display pattern control. [Figure 19] It is a diagram showing an example of cascade connection. [Figure 20] It is a functional block diagram of each light curtain connected in series. [Figure 21] It is a diagram showing old and new projection controls. [Figure 22] It is a diagram showing the startup flow of a projector. [Figure 23] It is a diagram showing the startup flow of a light receiver. [Figure 24]This figure shows the first example of a phase shift (2 series, 1 / 2 period shift). [Figure 25] This figure shows a second example of phase shift (3 series, 1 / 2 period shift). [Figure 26] This figure shows the third example of phase shift (3 series, 1 / 3 period shift). [Figure 27] This shows an example of interference prevention settings. [Figure 28] This figure shows an example of optical interference between multiple multi-axis photoelectric sensors. [Modes for carrying out the invention]

[0019] <Light Curtain> Figure 1 shows a schematic configuration of a light curtain. The light curtain 1 in this example configuration is one form of a multi-optical axis photoelectric sensor and generally comprises a pair of light emitters 100 and light receivers 200.

[0020] The light curtain 1 detects a person or object depending on whether at least one of the multiple optical axes (six optical axes Oax1 to Oax6 in this figure) that are spaced apart between the parallel-arranged light emitters 100 and light receivers 200 is blocked from light. For example, the light curtain 1 can be installed at the entrance or exit of a hazardous area where hazardous sources such as press equipment are placed, and used as a safety device to detect the intrusion or presence of workers.

[0021] The light emitter 100 and the light receiver 200 each comprise a long (maximum of 2m or more) housing 110 and 210, and cables 120 and 220 connected thereto.

[0022] The housing 110 has a hollow metal case 111 extending in the longitudinal direction, and hollow end caps 112 and 113 (corresponding to end members) connected to both ends of the metal case 111, respectively. Similarly, the housing 210 has a hollow metal case 211 extending in the longitudinal direction, and hollow end caps 212 and 213 (corresponding to end members) connected to both ends of the metal case 211, respectively. In this embodiment, the longitudinal direction is a direction substantially parallel to the direction in which the multiple optical axes formed between the light emitter 100 and the light receiver 200 are spaced apart from each other.

[0023] Thus, by using high-rigidity metal cases 111 and 211 as the cases for housings 110 and 210, the long housings 110 and 210 become less prone to deformation. Consequently, adjusting the placement of the light emitter 100 and light receiver 200 (for example, adjusting the angle to position them parallel) becomes relatively easy. Alternatively, inexpensive and lightweight extruded aluminum products may be used as the metal cases 111 and 211. In that case, the cross-section of the metal cases 111 and 211 will be the same shape regardless of where they are cut in the extrusion direction (=longitudinal direction).

[0024] The end caps 112, 113, 212, and 213 may each be formed by injection molding using a resin material, or by die casting using a metal material such as zinc. The lower end caps 113 and 213 in this figure may be fitted with interfaces for cables 120 and 220. Therefore, the end caps 113 and 213 may be larger than the upper end caps 112 and 212 in this figure.

[0025] <Floodlight> Figures 2 and 3 are perspective and front views, respectively, showing the overall configuration of the floodlight 100. Figure 4 is a perspective view showing one end of the floodlight 100.

[0026] As mentioned earlier, the floodlight 100 comprises a housing 110 and a cable 120. The housing 110 also includes a metal case 111 and end caps 112 and 113. Furthermore, the floodlight 100 includes a front cover 130, an indicator light 140, and a bumper section 150.

[0027] The front cover 130 is a long, translucent plate attached to cover the front opening (=detection window) of the housing 110. In the front opening of the housing 110, light-emitting elements 161 to 166, each for forming multiple optical axes Oax1 to Oax6, are arranged at equal intervals along the longitudinal direction. In other words, the front cover 130 is attached to the housing 110 so as to intersect with the multiple optical axes Oax1 to Oax6. The front cover 130 may be an extruded translucent resin plate (such as an acrylic plate) or a glass plate. In this embodiment, the translucency of the material used as the front cover 130 refers to a translucency such that the light from the light-emitting elements 161 to 166 forming the multiple optical axes Oax1 to Oax6 is not excessively diffused outside the optical axis, and is received by the light-receiving elements 261 to 266 (described later) with a certain amount of light or more. Since the front cover 130 is made of a light-transmitting material, the worker can see the light-emitting elements 161-166 through the front cover 130.

[0028] Furthermore, it is preferable that the end cap 113 has a light-emitting element (light-emitting element 166 in Figure 3) corresponding to at least one of the multiple optical axes Oax1 to Oax6. That is, it is preferable that the light-emitting elements 161 to 166 be arranged at equal intervals in the longitudinal direction over the entire length of the floodlight 100 from one end to the other. Also, it is preferable that the cable 120 extends from the back (or side) of the end cap 113 rather than from the bottom surface of the end cap 113. With this configuration, the floodlight 100 can be installed very close to the installation surface (floor, etc.). Therefore, dead space can be eliminated.

[0029] The indicator light 140 is controlled to flash on and off with a light color corresponding to, for example, the operating status of the light curtain 1 (such as the optical axis detection status and self-diagnosis results) or work instructions regarding the loading and unloading of objects. In other words, the indicator light 140 functions as an operation indicator light or a work instruction light. Therefore, by looking at the indicator light 140 of the light curtain 1, the worker can visually recognize the operating status of the light curtain 1 or work instructions.

[0030] In particular, the indicator light 140 is positioned longitudinally outward from at least one of the outer surfaces of the front cover 130 and the housing 110, or is formed in series with the front cover 130 (details of the structure will be described later). Referring to this figure, the indicator light 140 is provided on both sides of the front cover 130. With the indicator light 140 positioned or formed in this manner, a highly visible display can be provided without impairing the rigidity of the housing 110. More specifically, the indicator light 140 is a long extruded product, and is positioned so that the longitudinal direction of the indicator light 140 is aligned with the longitudinal direction of the housing 110. Note that the indicator light 140 only needs to be positioned along the longitudinal direction of the housing 110, and its manufacturing method is not limited to extrusion molding, and the shape of the indicator light 140 does not have to be long. For example, a configuration in which multiple members that function as indicator lights 140 are positioned along the longitudinal direction of the housing 110 is also possible.

[0031] Furthermore, the indicator light 140 is a light-diffusing member that diffuses light incident from an indicator light source 170 (not shown) housed inside the housing 110 in various directions. More specifically, the indicator light 140 contains a light diffuser that diffuses light in various directions. In a configuration where the light-diffusing member of the indicator light 140 contains a light diffuser, the indicator light 140 can be illuminated relatively uniformly even if the indicator light source 170 is small relative to the surface size of the indicator light 140, thus enabling a highly visible display. In this embodiment, the indicator light 140 is made of a transparent resin to which fine particles have been added, and is therefore milky white. If the base resin is not transparent but a specific color, the color will be a mixture of that specific color and milky white. In addition to the configuration containing a light diffuser, the indicator light 140 can also be made of a milky white resin (such as silicone) to achieve relatively uniform illumination. The light-diffusing member for the indicator light 140 can be any member that diffuses the light from the indicator light source 170 so that it can be seen from more directions, or any member that diffuses the light from the indicator light source 170 to such an extent that the outline of the indicator light source 170 is difficult to see from outside the indicator light 140. For example, a light-diffusing member whose surface is processed to diffuse the light from the indicator light source 170 may be arranged as the indicator light 140. As a surface processing that diffuses light, for example, texturing is known. With a configuration in which a light-diffusing member with a processed surface is arranged as the indicator light 140, it becomes easier to manufacture a member that has a region that diffuses light relatively easily and a region that does not diffuse light relatively easily.

[0032] The bumper section 150 protrudes outward from the region of the front cover 130's outer surface that intersects with multiple optical axes Oax1 to Oax6, and is positioned along the longitudinal direction of the housing 110 (details of the structure will be described later).

[0033] As shown in the figure, the bumper sections 150 are formed in pairs, protruding from both sides of the front cover 130. In other words, the front cover 130 is positioned in a narrow valley between the pair of bumper sections 150 (the twin bumpers proposed by the applicant) located on both sides and rising forward. Therefore, even if an object collides with the front of the floodlight 100, the impact is absorbed by the bumper sections 150. Consequently, the front cover 130 is less likely to be damaged. The bumper sections 150 may be made of a hard material such as metal.

[0034] Furthermore, the configuration of the light receiver 200 is basically the same as that of the light emitter 100. Therefore, in the explanatory text for Figures 2 to 4, the configuration of the light receiver 200 can be understood by appropriately substituting light emitter 100 and light-emitting elements 161 to 166 with light receiver 200 and light-receiving elements 261 to 266, respectively, and appropriately substituting other 100-series codes with 200-series codes. The same applies to the explanations that follow.

[0035] <Function Block> Figure 5 is a functional block diagram of the light curtain 1. In the light curtain 1 of this configuration example, the floodlight 100 includes an indicator light 140, light-emitting elements 161 to 166, a light source 170 for the indicator light, a control circuit 181, and a communication circuit 182.

[0036] The light-emitting elements 161 to 166 are arranged at equal intervals along the longitudinal direction of the light emitter 100 at a predetermined pitch. Based on the light emission control signal input from the control circuit 181, the light-emitting elements 161 to 166 sequentially emit multiple light beams toward the light receiver 200 (particularly the light-receiving elements 261 to 266) in a time-division manner to form multiple optical axes Oax1 to Oax6, respectively. Note that the light-emitting elements 161 to 166 may be, for example, light-emitting diodes that emit infrared light.

[0037] The indicator light source 170 supplies light to the indicator light 140 for display purposes based on the display control signal input from the control circuit 181. The indicator light source 170 may be capable of switching between multiple light emission colors (e.g., red, green, and orange) depending on the operating state of the light curtain 1 or work instructions.

[0038] Furthermore, the indicator light source 170 is preferably pulsed on at a timing that is temporally offset from the light emission / reception timing of each of the multiple optical axes Oax1 to Oax6. With this type of on / off control, interference with optical axis detection by the indicator light source 170 can be suppressed.

[0039] The indicator light 140 diffuses the light incident from the indicator light source 170 in various directions. By looking at the indicator light 140, the worker can visually recognize the operating status of the light curtain 1 or work instructions.

[0040] The control circuit 181 receives instructions from the light receiver 200 and generates a light emission control signal to sequentially drive the light-emitting elements 161 to 166 in a time-division manner. The control circuit 181 also generates a display control signal to turn the indicator light source 170 on and off with an arbitrary emission color. Furthermore, the control circuit 181 exchanges various information with the communication circuit 182.

[0041] The communication circuit 182 communicates with the light receiver 200 (particularly the communication circuit 282) via wired or wireless means. For example, the communication circuit 182 receives input from the light receiver 200 regarding the operating status of the light curtain 1 (such as the optical axis detection status and self-diagnosis results) and transmits it to the control circuit 181.

[0042] On the other hand, the light receiver 200 includes an indicator light 240, light receiving elements 261 to 266, a light source 270 for the indicator light, a control circuit 281, a communication circuit 282, an output circuit 283, and an input circuit 284.

[0043] The light-receiving elements 261 to 266 are arranged at equal intervals along the longitudinal direction of the light receiver 200, with the same pitch as the light-emitting elements 161 to 166. Based on the light-receiving control signal input from the control circuit 281, the light-receiving elements 261 to 266 sequentially receive multiple light beams in a time-division manner to form multiple optical axes Oax1 to Oax6. The light-receiving elements 261 to 266 may also be, for example, photodiodes or phototransistors that output an electrical signal corresponding to the amount of infrared light received.

[0044] The indicator light source 270 supplies light to the indicator light 240 for display based on the display control signal input from the control circuit 281. Like the indicator light source 170, the indicator light source 270 may be able to switch between multiple light emission colors (e.g., red, green, and orange) depending on the operating status of the light curtain 1 or work instructions.

[0045] Furthermore, the indicator light source 270 is preferably pulsed on at a timing that is temporally offset from the light emission / reception timing of each of the multiple optical axes Oax1 to Oax6. With this type of on / off control, interference with optical axis detection by the indicator light source 270 can be suppressed.

[0046] Furthermore, consider the case where the indicator light source 270 is continuously lit. In this case, even if the DC light from the indicator light source 270 is received by the light receiving elements 261 to 266, it is desirable to provide a saturation prevention circuit (= DC component subtraction circuit) so that the electrical signals output from the light receiving elements 261 to 266 do not become saturated.

[0047] The indicator light 240 diffuses the light incident from the indicator light source 270 in various directions. By looking at the indicator light 240, the worker can visually recognize the operating status of the light curtain 1 or work instructions.

[0048] Furthermore, since indicator lights 140 and 240 are provided on both the light emitter 100 and the light receiver 200, a highly visible display can be achieved.

[0049] The control circuit 281 generates a light receiving control signal to sequentially activate the light receiving elements 261 to 266 in a time-division manner, synchronized with the drive timing of each of the light-emitting elements 161 to 166. The control circuit 281 also generates a display control signal to turn the indicator light source 270 on and off with an arbitrary emission color. Furthermore, the control circuit 281 exchanges various information with the communication circuit 282, the output circuit 283, and the input circuit 284.

[0050] Furthermore, the control circuit 281 monitors the light-ingress / light-blocking state of each of the multiple optical axes Oax1 to Oax6. For example, the control circuit 281 may output an operation permission signal (ON signal) when all of the multiple optical axes Oax1 to Oax6 are in the light-ingress state. On the other hand, the control circuit 281 may output an operation disallowance signal (OFF signal) when at least one of the multiple optical axes Oax1 to Oax6 is in the light-blocking state.

[0051] Furthermore, the control circuit 281 may be equipped with a self-diagnosis function to determine whether it is in a state where it can correctly monitor the light-ingress / light-blocking state of each of the multiple optical axes Oax1 to Oax6. As a self-diagnosis method, for example, the control circuit 281 and the output circuit 283 (e.g., OSSD [Output Signal Switching Device] output) may be multiplexed, and the match / mismatch of the multiplexed signals may be determined.

[0052] For example, if the multiplexed signals match, an OK diagnosis (a diagnosis result indicating that the system is in a state where it can be properly monitored) is issued. On the other hand, if the multiplexed signals do not match, an NG diagnosis (a diagnosis result indicating that the system is not in a state where it can be properly monitored) is issued. In the event of an NG diagnosis, an operation prohibition signal (OFF signal) may be output regardless of the light input status of each of the multiple optical axes Oax1 to Oax6.

[0053] Information that can be used for safety control is designated as safety information, while general information that cannot be used for safety control is designated as non-safety information. For example, the OSSD output is a type of safety information. The signals used to control the on / off state of the indicator light sources 170 and 270 may be signals indicating safety information or signals indicating non-safety information.

[0054] The communication circuit 282 communicates with the floodlight 100 (particularly the communication circuit 182) by wire or wireless means. The communication circuit 282 receives information from the control circuit 281 regarding the operating status of the light curtain 1 (such as the optical axis detection status and self-diagnosis results) and transmits it to the floodlight 100.

[0055] The output circuit 283 communicates with external devices (e.g., safety controllers) via wired or wireless means. For example, the output circuit 283 receives input from the control circuit 281 regarding the operating status of the light curtain 1 (such as the optical axis detection status and self-diagnosis results) and transmits it to the external devices.

[0056] The input circuit 284 communicates with external devices (e.g., safety controllers) via wired or wireless means. For example, the input circuit 284 receives input from external devices regarding work instructions for loading and unloading objects and transmits them to the control circuit 281.

[0057] <First Embodiment> Figure 6 is a diagram showing a first embodiment of the floodlight 100 (a schematic cross-sectional view when the metal case 111 of the floodlight 100 is cut at an arbitrary position in the longitudinal direction). The floodlight 100 of this embodiment comprises a housing 110 (only the metal case 111 is depicted in this figure), a front cover 130, an indicator light 140, a bumper portion 150, a light source for the indicator light 170, a circuit board 190, and a light shielding plate 191.

[0058] The metal case 111 is an extruded product that extends in the longitudinal direction of the floodlight 100. As shown in the figure, the metal case 111 consists of a main body 111a, a pair of first protrusions 111b, and a pair of second protrusions 111c.

[0059] The main body 111a is a hollow member with a U-shaped cross-section and an opening on the upper side of the paper (= the front side of the floodlight 100). The internal space of the main body 111a houses the indicator light source 170, the substrate 190, and the light shielding plate 191.

[0060] A pair of first protruding strips 111b project inward from the inner surfaces of the left and right walls of the main body 111a toward the inside of the opening. That is, the pair of first protruding strips 111b are arranged facing each other at a predetermined distance, straddling the optical axis intersection region X (= the region where multiple optical axes Oax1 to Oax6 intersect). The pair of first protruding strips 111b also function as cover mounting parts for supporting the front cover 130. As described above, a translucent material is used for the front cover 130, but it is sufficient that at least the optical axis intersection region X is translucent and the optical axes Oax1 to Oax6 are not obstructed. For example, in this embodiment, the portion that contacts the pair of first protruding strips 111b does not necessarily have to be translucent.

[0061] A pair of second protrusions 111c extend further upward from the upper ends of the left and right walls of the main body 111a. Furthermore, the tips of each of the second protrusions 111c are bent inward towards the opening. The pair of second protrusions 111c function as a bumper portion 150 to protect the front cover 130. In this embodiment, the aforementioned bumper portion 150 is formed from the metal case 111. Therefore, the robustness of the floodlight 100 can be increased.

[0062] The front cover 130 is supported (suspended) at both ends, straddling a pair of first protruding strips 111b. The front cover 130 allows light to pass through that forms multiple optical axes Oax1 to Oax6 in the optical axis intersection region X. The area between the front cover 130 and the pair of first protruding strips 111b (see thick line α) is treated to improve liquid resistance. For example, a packing is placed, or it is bonded with a liquid-resistant adhesive. As will be described later, the indicator light 140 increases the adhesion between the front cover 130 and the first protruding strips 111b, further improving liquid resistance.

[0063] The indicator lights 140 are positioned on both sides of the front cover 130, adjacent to the bumper section 150. Referring to this figure, the indicator lights 140 are positioned along the longitudinal direction of the floodlight 100 in the area sandwiched between the tip (bent portion) of the first protruding strip 111b and the second protruding strip 111c, that is, in the area sandwiched between the bumper section 150 and the front cover 130.

[0064] The indicator light 140 diffuses the light incident from the indicator light source 170 through the front cover 130 in various directions. For example, the indicator light 140 may be provided with a taper to refract and diffuse the light incident from the indicator light source 170 toward the inside of the opening.

[0065] With the indicator lights 140 arranged in this manner, they are easily visible even from the side of the floodlight 100. Therefore, in a small (slim-diameter) light curtain 1 using a metal case 111, highly visible displays can be provided without compromising the rigidity of the housing 110. In particular, when a pair of bumper sections 150 are provided protruding from both sides of the front cover 130, the improvement in visibility due to the above arrangement can become even more pronounced.

[0066] Furthermore, in the floodlight 100 of this embodiment, the indicator light 140 also functions as a pressing member for pressing and fixing the front cover 130 downward (towards the first protruding strip 111b). Therefore, the airtightness between the front cover 130 and the first protruding strip 111b is increased, which prevents liquid from entering the inside of the metal case 111 and improves liquid resistance. In order for the indicator light 140 to function as a pressing member, it is desirable that the indicator light 140 has appropriate elasticity.

[0067] The indicator light source 170 is mounted on the main surface of the substrate 190 (= the surface facing the front cover 130). The indicator light source 170 supplies light for display to the indicator light 140 via the front cover 130. As shown in this figure, the light emitted from the indicator light source 170 passes between the pair of first protruding strips 111b without being obstructed by the pair of first protruding strips 111b and is supplied to the indicator light 140 via the front cover 130.

[0068] The number of indicator light sources 170 is not limited. For example, the indicator light sources 170 may be arranged intermittently in multiple locations along the longitudinal direction of the floodlight 100, or they may be formed in a continuous series.

[0069] Furthermore, the indicator light source 170 may be equipped with a lens for controlling the direction of the emitted light. For example, a lens may be provided that is optically designed to reduce the angle of light spread in the left-right direction of the figure and increase the angle of light spread in the depth direction of the figure. Such a lens makes it possible to reduce the number of indicator light sources 170 while suppressing interference with multiple optical axes Oax1 to Oax6.

[0070] The type of lens may be a point-symmetric lens (single arrangement) or a cylindrical lens (series arrangement of extruded products).

[0071] The light-shielding plate 191 is provided between the indicator light source 170 and the optical axis intersection region X. Therefore, since the light from the indicator light source 170 toward the optical axis intersection region X is blocked, the light emitted from the indicator light source 170 is less likely to interfere with the multiple optical axes Oax1 to Oax6.

[0072] Furthermore, consider the case where the optical axis Oax1 to Oax6 is formed by infrared light, and visible light (red light, green light, or orange light, etc.) is emitted from the indicator light source 170. In this case, a filter that transmits infrared light and blocks visible light may be provided in the light receiver 200. In particular, when an indicator light 240 is provided in the light receiver 200, it is sufficient to have a configuration in which a filter that transmits infrared light and blocks visible light is arranged so as not to obstruct the display of the indicator light 240. The filter may be provided in the light receiving elements 261 to 266, or it may be provided in the lens that guides light to the light receiving elements 261 to 266.

[0073] Figure 7 shows an example of the arrangement of the indicator light source 170 in the first embodiment. As shown in this figure, the light-emitting elements 161 to 166 may be arranged at equal intervals along the longitudinal direction of the substrate 190 in the central region 190a of the substrate 190. On the other hand, the indicator light source 170 may be arranged at equal intervals along the longitudinal direction of the substrate 190 in the end region 190b of the substrate 190.

[0074] In particular, the light-emitting elements 161-166 and the indicator light source 170 may be arranged so that their positions in the longitudinal direction of the substrate 190 are offset from each other (staggered). With such an arrangement, mutual interference between the light-emitting elements 161-166 and the indicator light source 170 is suppressed.

[0075] The number and arrangement of the indicator light sources 170 are not limited to the arrangement example shown in this figure. For example, the number of indicator light sources 170 may be reduced so that there is some unevenness in the light supplied to the indicator lights 140.

[0076] <Display contents> Figure 8 shows the relationship between the light emission color of the indicator light 140 and its operating mode. As shown in this figure, the indicator light 140 can be switched between operation indicator light mode and work indicator light mode. For example, the control signal for switching the operating mode of the indicator light 140 may be a 2-bit (4-value) digital signal input to the input circuit 284.

[0077] First, let's explain the case where the indicator light 140 is set to operation indicator light mode. When the indicator light 140 is set to operation indicator light mode, it is controlled to turn on and off with a light color corresponding to the operating status of the light curtain 1.

[0078] Referring to this diagram, for example, when the light curtain 1 is in a normal state (for example, when none of the multiple optical axes Oax1 to Oax6 are blocked), the indicator light 140 lights up green. On the other hand, when the light curtain 1 is in an abnormal state (for example, an emergency stop state where at least one of the multiple optical axes Oax1 to Oax6 is blocked), the indicator light 140 lights up red. Also, when the light curtain 1 is in an alarm notification state (for example, an NG diagnosis state by the self-diagnosis function), the indicator light 140 flashes red.

[0079] Next, we will describe the case when the indicator light 140 is set to work instruction light mode. When the indicator light 140 is set to work instruction light mode, it is controlled to turn on and off with a light color corresponding to the work instruction signal received by the input circuit 284.

[0080] Referring to this diagram, for example, when the work instruction signal indicates "work permitted," the indicator light 140 lights up green. On the other hand, when the work instruction signal indicates "work prohibited," the indicator light 140 lights up red. Also, when the work instruction signal indicates "self-diagnosis," the indicator light 140 blinks red. In addition, in work instruction light mode, the indicator light 140 may light up orange. The way in which these lighting states are used may vary depending on the user.

[0081] Furthermore, if the light curtain 1 is used in an environment where the illumination of the indicator light 140 is undesirable, it is possible to keep the indicator light 140 constantly off.

[0082] <Considerations regarding the decrease in light intensity of optical bearings> As explained earlier, a light curtain consists of two components: a light emitter and a light receiver, with multiple light-emitting and light-receiving elements arranged axially. When using a light curtain, the light emitter and light receiver should be positioned parallel to each other, and their angles adjusted so that light is received by all elements. The greater the distance between the light emitter and light receiver, the more difficult it becomes to determine if the orientation is correct, and the harder it is to see the display. Therefore, adjusting the angles becomes more difficult.

[0083] Light curtains are sometimes used in harsh environments where they may be exposed to dirt or impacts. Therefore, some products feature a bumper-shaped protrusion extending beyond the front cover to protect the detection unit's front cover. However, preventing dirt from accumulating on the front cover is difficult. If dirt builds up and the light-receiving element can no longer receive sufficient light, the optical axis may become obscured, potentially causing the device to shut down due to a safety output from the light curtain. Therefore, maintenance cleaning of the front cover's glass surface is necessary before it affects the optical axis detection results.

[0084] In environments where dirt accumulates, it is necessary to install light curtains to ensure sufficient optical bearing light intensity to compensate for the decrease in optical bearing light intensity (= the amount of light received by each optical axis, which is the criterion for determining whether or not the optical axis is in a state of light blocking) due to dirt. Furthermore, it is necessary to monitor the decrease in optical bearing light intensity over time and perform maintenance before the optical axis becomes completely blocked.

[0085] In response to the above requirements, there are models of light curtains that allow you to check the light bearing intensity on the unit itself. For example, some existing models express the light bearing intensity by the number of lit LEDs (light-emitting diodes) or by a 7-segment digital display. However, these displays are small and difficult to see from a distance. Therefore, it can be difficult to check the display when installing and adjusting the light curtain. Also, even during operation of the light curtain, it is difficult to notice a decrease in the light bearing intensity unless you consciously check the small display mentioned above.

[0086] On the other hand, the light curtain 1 described herein is equipped with large indicator lights 140 and 240 so that the operating status of the light curtain 1 can be easily seen, while maintaining both miniaturization and high visibility.

[0087] In light of the above considerations, we propose a novel embodiment below in which the highly visible indicator lights 140 and 240 described above can display information linked to the light intensity of the optical bearing.

[0088] <Second Embodiment> Figure 9 shows an example of the arrangement of light sources for indicator lights in the second embodiment. In this embodiment, multiple (two in this figure) substrates 190 having the same structure are cascaded along the longitudinal direction. With such a configuration, the length of the light curtain 1 can be easily increased simply by increasing the number of cascaded substrates 190.

[0089] In this figure illustrating the light emitter 100, the light-emitting elements 161 to 166 may be arranged at equal intervals along the longitudinal direction of the substrate 190 in the central region 190a of the substrate 190, as in Figure 7 above. Referring to this figure, on the substrate 190 on the right side of the page, the light-emitting elements 161 to 163 are arranged from right to left in the order shown in the figure. On the other hand, on the substrate 190 on the left side of the page, the light-emitting elements 164 to 166 are arranged from right to left in the order shown in the figure. When understanding the configuration of the light receiver 200, the light-emitting elements 161 to 166 can be replaced with light-receiving elements 261 to 266, respectively.

[0090] On the other hand, the indicator light sources 170 may be arranged at equal intervals along the longitudinal direction of the substrate 190 in the edge region 190b of the substrate 190. In particular, the indicator light sources 170 can be distinguished as indicator light sources 170a, 170b, and 170c depending on the differences in their respective control systems. Referring to this figure, the indicator light sources 170a, 170b, and 170c are arranged on the two substrates 190 in the order shown, from left to right on the page. Although not shown in this figure, the light curtain 1 is equipped with an OSSD indicator light whose display mode changes according to the OSSD output, separate from the indicator light sources 170. Therefore, the display mode of the indicator light sources 170 changes to indicate the light receiving state of the light receiving elements 261 to 266.

[0091] As described above, the light-emitting elements 161-163 (or 164-166) and the indicator light sources 170a, 170b, and 170c are arranged as a single unit on a common substrate 190. In particular, the indicator light sources 170a, 170b, and 170c are unitized as a set of three.

[0092] As a variation, the light-emitting elements 161-163 (or 164-166) and the indicator light sources 170a, 170b, and 170c may each be separate units. That is, the unit in which the light-emitting elements 161-163 (or 164-166) are arranged and the unit in which the indicator light sources 170a, 170b, and 170c are arranged may be independent.

[0093] Figure 10 shows an example of a display pattern in the second embodiment. The upper part of this figure depicts the "a-lighted state". In this "a-lighted state", the indicator light source 170a is lit, while both indicator light sources 170b and 170c are off. Therefore, the display pattern is one light on, two lights off, repeated from left to right on the page.

[0094] The middle section of this diagram depicts the "ab-lighted state." In this "ab-lighted state," both indicator light sources 170a and 170b are lit, while indicator light source 170c is off. Therefore, the display pattern repeats from left to right on the page, with "two lights on, one off."

[0095] The lower part of this diagram depicts the "abc lit state." In this "abc lit state," the indicator light sources 170a, 170b, and 170c are all lit.

[0096] Thus, in the example display pattern of this embodiment, the indicator light sources 170a, 170b, and 170c are illuminated at appropriate intervals. Therefore, by switching the display pattern to one of the three above according to the optical bearing light intensity, the optical bearing light intensity can be determined simply by looking at the large indicator lights 140 and 240. As a result, a light curtain 1 is provided that is easy to adjust during initial setup and has high maintainability.

[0097] <Third Embodiment> Figure 11 shows an example of the arrangement of indicator light sources and an example of a display pattern in the third embodiment. In this embodiment, two each of the indicator light sources 170a, 170b, and 170c are arranged on a common substrate 190 as a single unit. That is, the indicator light sources 170a, 170b, and 170c are unitized in sets of six.

[0098] Referring to this figure, the circuit board 190 has two indicator light sources 170a, 170b, and 170c arranged in the order shown, from left to right on the page.

[0099] The upper part of this diagram depicts the "a-lighting state." In this "a-lighting state," indicator light source 170a is lit, while indicator light sources 170b and 170c are both off. Therefore, the display pattern repeats from left to right on the page, with "two lights on, four lights off."

[0100] The middle section of this diagram depicts the "ab-lighted state." In this "ab-lighted state," both indicator light sources 170a and 170b are lit, while indicator light source 170c is off. Therefore, the display pattern repeats from left to right on the page, with "four lights on, two off."

[0101] The lower part of this diagram depicts the "abc lit state." In this "abc lit state," the indicator light sources 170a, 170b, and 170c are all lit.

[0102] In the second embodiment described above (Figure 10), the number of indicator light sources 170a, 170b, and 170c, which are in a non-lit state (off state), is increased or decreased by one for each display pattern, such as 2, 1, and 0.

[0103] On the other hand, in the example arrangement of indicator light sources and display patterns of this embodiment, the number of indicator light sources 170a, 170b, and 170c that are not lit increases or decreases by two for each display pattern, to 4, 2, and 0, respectively. Therefore, compared to the second embodiment described above (Figure 10), the difference in distance between the light sources that are partially lit becomes larger. As a result, it becomes easier to recognize the switching of the display pattern (and consequently the change in the amount of light in the optical bearing) even when passing through the light diffuser.

[0104] <Fourth Embodiment> Figure 12 shows an example of the arrangement of indicator light sources and an example of the display pattern in the fourth embodiment. In this embodiment, as in the second embodiment (Figure 10) described above, the indicator light sources 170a, 170b, and 170c are unitized as a set of three. However, the arrangement order of the indicator light sources 170a, 170b, and 170c differs for each substrate 190.

[0105] Referring to this figure, on the circuit board 190 on the left side of the figure, indicator light sources 170a, 170b, and 170c are arranged in the order shown, from left to right on the page. On the other hand, on the circuit board 190 on the right side of the figure, indicator light sources 170a, 170b, and 170c are arranged in the order shown, from right to left on the page.

[0106] The upper part of this diagram depicts the "a-lighting state." In this "a-lighting state," indicator light source 170a is lit, while indicator light sources 170b and 170c are both off. Therefore, the display pattern repeats from left to right on the page: "one lit, four off, one lit."

[0107] The middle section of this diagram depicts the "ab-lighted state." In this "ab-lighted state," both indicator light sources 170a and 170b are lit, while indicator light source 170c is off. Therefore, the display pattern repeats from left to right on the page: "one off, four on, one off."

[0108] Thus, with the example arrangement of indicator light sources and display patterns in this embodiment, while maintaining a set of three units, the number of indicator light sources 170a, 170b, and 170c that are not illuminated increases or decreases by two for each display pattern, such as 4, 2, and 0. Therefore, as with the third embodiment described above (Figure 11), it becomes easier to recognize the switching of the display pattern (and consequently the change in the light intensity of the optical bearing).

[0109] <Relationship between optical bearing light intensity and display pattern> Figure 13 shows the relationship between the optical bearing light intensity (average light received) and the display pattern. The optical bearing light intensity is converted by an A / D converter and compared with a threshold. The criterion for determining the display pattern may also be the average value of the light received at each optical axis (= average light received).

[0110] First, the ON state of the OSSD indicates that the condition "the amount of light received by all optical axes is above the first threshold" is met for the photodetectors 261 to 266, and the OSSD output is ON. In this embodiment, for convenience, the state in which the photodetectors 261 to 266 meet this condition and the OSSD output can be turned ON is defined as the ON state, and the ON state is the state in which "the amount of light received by all optical axes is above the first threshold." The first threshold mentioned above is the same as the threshold used to determine whether each individual optical axis is in a light-shielding state or not. Therefore, the average amount of light received in that state is relatively high and cannot be as low as a value considered to be "completely shielded." In other words, since the amount of light received by all optical axes is above the first threshold, it is impossible for the average amount of light received to fall below the first threshold.

[0111] Therefore, the "off" display when the average light reception amount falls below the first threshold can be understood as a display mode that exists only when the light-receiving elements 261-266 do not satisfy the condition that "the light reception amount for all optical axes is above the first threshold," i.e., when the judgment is OFF. In this figure, a horizontal axis is introduced to clarify this. The horizontal axis shows the result of the individual light reception amount judgment for each optical axis (= the number of optical axes judged to be in a shaded state by the individual optical axis judgment). Note that the OSSD OFF state indicates that the condition that "the light reception amount for all optical axes is above the first threshold" is not satisfied for the light-receiving elements 261-266, and the OSSD output is OFF. In this embodiment, for convenience, the judgment OFF state is defined as the state when the light-receiving elements 261-266 do not satisfy the condition that "the light reception amount for all optical axes is above the first threshold," i.e., when "the light reception amount for at least one optical axis is below the first threshold." In other words, in the judgment ON state, the number of shaded optical axes is 0. On the other hand, in the judgment OFF state, the number of shaded optical axes is 1 or more.

[0112] It should be noted that the individual light reception amount judgment for each optical axis is solely for switching between the judgment ON state (display color: green) and the judgment OFF state (display color: red). Therefore, the step for making this judgment in the flowchart shown later is the same step as the step for comparing the average light reception amount with the threshold.

[0113] Furthermore, the thresholds used to determine the number of illuminated indicator light sources 170a, 170b, and 170c are shifted between the ON and OFF states. First, let's explain the ON state. As mentioned earlier, the ON state is when the amount of light received by all optical axes is above the first threshold. Therefore, in the ON state, thresholds for switching the number of illuminated lights (the fourth and fifth thresholds in this diagram) are set in the region where the average amount of light received is relatively high.

[0114] As shown in this diagram, when the judgment is ON and the average light received is lower than the fourth threshold, one green light will illuminate (meaning only the indicator light source 170a will be illuminated green). When the average light received is higher than the fourth threshold but lower than the fifth threshold, two green lights will illuminate (meaning both indicator light sources 170a and 170b will be illuminated green). When the average light received is higher than the fifth threshold, three green lights will illuminate (meaning indicator light sources 170a, 170b, and 170c will be illuminated green). In other words, the number of illuminated green lights increases as the average light received increases.

[0115] Furthermore, the amount of light received by each optical axis decreases as the distance between the light emitter 100 and the light receiver 200 increases. It is conceivable that even if the light emitter 100 and the light receiver 200 are installed parallel to each other as specified, and are free of dirt and receiving light normally, the amount of light received may decrease solely due to an increase in the distance between the light emitter 100 and the light receiver 200.

[0116] In this situation, reducing the number of illuminated indicator light sources 170a, 170b, and 170c would prevent the correct transmission of information related to installation and maintenance. Therefore, it is desirable to set the threshold so that the range in which three indicator light sources 170a, 170b, and 170c are illuminated is wide. Referring to this figure, in the ON state of the judgment, the fifth threshold for switching between three illuminated indicator light sources 170a, 170b, and 170c and two illuminated is set relatively low.

[0117] Next, we will explain the OFF state. Switching the display pattern in the OFF state is useful when installing the light emitter 100 and light receiver 200. For example, consider the case where you start from an off state with 0 lights on and adjust the installation positions of the light emitters 100 and 200. In this case, it is desirable that the display pattern switches even if the average light received increases or decreases only slightly, in order to understand the direction of the adjustment (i.e., whether or not you are approaching the correct installation position).

[0118] Therefore, in the OFF state, thresholds for switching the number of lights on (first threshold, second threshold, and third threshold in this figure) are set in a region where the average light reception is relatively low. For example, the relationship between the thresholds may be first threshold < second threshold < third threshold < fourth threshold < fifth threshold, as shown in this figure. In the embodiment shown in this figure, the first threshold, second threshold, and third threshold do not affect the switching of the number of lights on in the ON state.

[0119] As shown in the diagram, when the judgment is OFF and the average light received is lower than the first threshold, the lights will be off as previously described (= the indicator light sources 170a, 170b, and 170c will be turned off). When the average light received is higher than the first threshold but lower than the second threshold, one red light will be on (= only indicator light source 170a will be lit red). When the average light received is higher than the second threshold but lower than the third threshold, two red lights will be on (= indicator light sources 170a and 170b will be lit red). When the average light received is higher than the third threshold, three red lights will be on (= indicator light sources 170a, 170b, and 170c will be lit red). In other words, the number of red lights increases as the average light received increases.

[0120] Thus, the purpose of switching the display pattern according to the light intensity of the optical bearing differs between the ON and OFF states. Specifically, the green light display pattern switch in the ON state is expected to be useful for identifying dirt accumulation (the need for maintenance) after the start of operation of Light Curtain 1. On the other hand, the red light display pattern switch in the OFF state is expected to be useful for adjusting the optical axis when installing Light Curtain 1. Therefore, in order to individually set the optimal threshold for the ON and OFF states, it is desirable to stagger the thresholds between the ON and OFF states.

[0121] However, conversely, there are also advantages to setting the thresholds to match the ON and OFF states. For example, in this diagram, looking only at the average light reception, the "one green light" in the ON state and the "three red lights (or two red lights)" in the OFF state are adjacent. Therefore, when the optical axis is blocked while maintaining the average light reception, and the system switches from the ON state to the OFF state, the display pattern switches from "one green light" to "three red lights (or two red lights)".

[0122] In other words, if we focus solely on the number of lights illuminated, there is a risk of an unnatural display pattern switching where the number of lights illuminated increases even though the optical axis is blocked. Therefore, if the priority is to clearly communicate the optical axis light intensity, it is desirable to keep the threshold the same for the ON and OFF states of the judgment to prevent the aforementioned reversal of the number of lights illuminated.

[0123] Figure 14 shows the relationship between the light intensity of the optical bearing (minimum light intensity) and the display pattern. As shown in this figure, the criterion for determining the display pattern may be the minimum value of the amount of light received at each optical axis (= minimum light intensity).

[0124] In this case, for example, a first threshold, a second threshold, and a third threshold may be set. The relationship between each threshold may be first threshold < second threshold < third threshold.

[0125] As shown in this diagram, when the minimum light intensity is lower than the first threshold, three red lights illuminate (= indicator light sources 170a, 170b, and 170c are illuminated in red). This state corresponds to the OFF state. Thus, in the OFF state, the number of illuminated red lights is fixed at three. When the minimum light intensity is higher than the first threshold but lower than the second threshold, one green light illuminates (= only indicator light source 170a is illuminated in green). When the minimum light intensity is higher than the second threshold but lower than the third threshold, two green lights illuminate (= indicator light sources 170a and 170b are illuminated in green). When the minimum light intensity is higher than the third threshold, three green lights illuminate (= indicator light sources 170a, 170b, and 170c are illuminated in green). In other words, the number of illuminated green lights increases as the minimum light intensity increases.

[0126] Thus, as a criterion for determining the display pattern, either the average value of the amount of light received in each optical axis (= average light received) or the minimum value (= minimum light received) may be used.

[0127] <Image of lights up> Figure 15 shows an image of the lighting of the light curtain 1 (first example). In this figure, the arrangement example of the indicator light sources 170a, 170b, and 170c and the display pattern are the same as those of the second embodiment described above (Figures 9 and 10). Furthermore, the relationship between the light intensity of the optical bearing and the display pattern is the same as the display pattern switching control described above in Figure 13.

[0128] First, let's explain the OFF state (the four states on the left side of this diagram). In the completely blackout state, light curtain 1 is turned off (= indicator light sources 170a, 170b, and 170c are turned off). At low light intensity, one red light is lit (= only indicator light source 170a is lit red). At medium light intensity, two red lights are lit (= indicator light sources 170a and 170b are lit red). At high light intensity, three red lights are lit (= indicator light sources 170a, 170b, and 170c are lit red).

[0129] Next, let's explain the ON state (the three states on the right in this diagram). At low light intensity, one green light is illuminated (= only indicator light source 170a is illuminated in green). At medium light intensity, two green lights are illuminated (= indicator light sources 170a and 170b are illuminated in green). At high light intensity, three green lights are illuminated (= indicator light sources 170a, 170b, and 170c are illuminated in green).

[0130] Furthermore, diffusers are placed above each of the indicator light sources 170a, 170b, and 170c. Therefore, it is desirable to appropriately set the arrangement and display patterns of the indicator light sources 170a, 170b, and 170c so that the change in the display pattern can be recognized even through the diffusers. This point has been mentioned earlier.

[0131] Figure 16 shows an image of the lighting of the light curtain 1 (second example). In this figure, the light curtain 1 displays a bar according to the light intensity of the optical bearing. Specifically, the three circuit boards 190x, 190y, and 190z (more precisely, a group of indicator light sources 170 incorporated into each) that are cascaded in the longitudinal direction of the light curtain 1 are each controlled to turn on and off as individual units.

[0132] First, let's explain the OFF state (the four states on the left side of this diagram). In the completely darkened state, light curtain 1 is turned off (= the circuit board 190x, 190y, and 190z are turned off). At low light intensity, 1 / 3 of light curtain 1 is illuminated in red (= only circuit board 190x is illuminated in red). At medium light intensity, 2 / 3 of light curtain 1 is illuminated in red (= circuit board 190x and 190y are illuminated in red). At high light intensity, the entire (3 / 3) of light curtain 1 is illuminated in red (= circuit board 190x, 190y, and 190z are illuminated in red).

[0133] Next, let's explain the ON state (the three states on the right in this diagram). With low light intensity, 1 / 3 of light curtain 1 will light up in green (= only circuit board 190x will light up in green). With medium light intensity, 2 / 3 of light curtain 1 will light up in green (= circuit boards 190x and 190y will light up in green). With high light intensity, the entire (3 / 3) of light curtain 1 will light up in green (= circuit boards 190x, 190y and 190z will light up in green).

[0134] Thus, with the lighting image of the second example (Figure 16), the switching of the display pattern according to the light intensity of the optical bearing is easier to understand compared to the first example (Figure 15). However, if the above lighting image is to be realized based on a configuration in which multiple circuit boards 190x, 190y, and 190z are cascaded, the design difficulty and cost may increase.

[0135] <Examples of display patterns according to the light intensity of the optical bearing> The above example illustrates a configuration in which the number of indicator light sources 170 illuminated (especially the decimation interval) is switched according to the light intensity of the optical bearing, but various other modifications are also possible.

[0136] For example, the indicator light 140 may be switched to change over time according to the amount of light from the optical bearing (for example, keeping the indicator light 140 constantly lit, flashing at 1-second intervals, or flashing at 2-second intervals). Alternatively, the amount of light emitted or the color of light emitted by the indicator light 140 may be switched according to the amount of light from the optical bearing. When these embodiments are adopted, it becomes unnecessary to individually control multiple indicator light sources 170 when switching display patterns. Therefore, it becomes possible to use, for example, an optical fiber as the indicator light 140.

[0137] <Functional block (with display pattern control function)> Figure 17 is a functional block diagram of the light curtain 1 equipped with a display pattern control function. Note that this figure is based on the previously mentioned Figure 5, but focuses on the control systems of the indicator light sources 170a, 170b, and 170c, and the indicator light sources 270a, 270b, and 270c, rather than the light emission / receiving systems of the optical axes Oax1 to Oax6.

[0138] Furthermore, in this figure, following the second embodiment described above (Figures 9 and 10), the indicator light sources 170a, 170b, and 170c, and the indicator light sources 270a, 270b, and 270c, are each arranged in sets of three in the order shown in the figure (a, b, c, a, b, c from the top of the page).

[0139] The control circuit 181 controls the two indicator light sources 170a with a common control signal. The same applies to the indicator light sources 170b and 170c. Similarly, the control circuit 281 controls the two indicator light sources 270a with a common control signal. The same applies to the indicator light sources 270b and 270c.

[0140] The amount of light received by each of the optical axes Oax1 to Oax6 is compared with a threshold value by the control circuit 281. In this case, the control circuit 281 may include an analog-to-digital conversion circuit that converts the analog signals output from each of the photodetectors 261 to 266 into digital signals. The control circuit 281 may also include a calculation circuit that calculates the average value (=average light received) or the minimum value (=minimum light received) from the light received by each of the optical axes Oax1 to Oax6.

[0141] The control circuit 281 controls the on / off states of the indicator light sources 270a, 270b, and 270c based on the comparison result between the average light received (or minimum light received) and a threshold. The control circuit 281 also transmits the above comparison result to the control circuit 181 via the communication circuits 282 and 182. The control circuit 181 controls the on / off states of the indicator light sources 170a, 170b, and 170c based on the above comparison result transmitted from the control circuit 281.

[0142] <Processing Flow> Figure 18 shows the processing flow for display pattern control based on the average light reception amount. When the processing flow shown in this figure starts, in step S1, the optical axis to be driven, Oax(i) (where i=1, 2, ... imax(6), and the initial setting value is i=1), is set.

[0143] In the following step S2, the light-emitting element 16i is turned on. Specifically, the light-emitting element 161, which forms the optical axis Oax1, is turned on first.

[0144] In step S3, it is determined whether the amount of light received by the light-receiving element 26i, Li, is greater than the first threshold. As mentioned earlier, the first threshold corresponds to the threshold used to determine whether each of the optical axes Oax1 to Oax6 is in a light-shielding state. If the result is yes, the flow proceeds to step S4. On the other hand, if the result is no, the flow proceeds to step S8. In step S8, the safety output (OSSD) is switched to the OFF state without waiting for the display pattern control to be completed. Therefore, it is possible to quickly stop hazardous sources such as press equipment. In addition to switching the safety output (OSSD) to the OFF state in step S8, the display pattern of the OSSD indicator light may also be changed in accordance with the switch to the OFF state of the safety output (OSSD). Steps S3 and S8 are not directly related to the display pattern control. For this reason, steps S3 and S8 are depicted with dashed lines in this figure.

[0145] If a "yes" determination is made in step S3, the amount of light received, Li, is recorded in a register or similar device in step S4.

[0146] In the following step S5, it is determined whether the optical axis is at its final position (i.e., i = imax(6)). If the result is yes, the flow proceeds to step S6. On the other hand, if the result is no, the variable i is incremented by one (++i), and the flow returns to step S1. From here on, steps S1 to S5 are repeated until the result in step S5 is yes.

[0147] If a "yes" determination is made in step S5, step S6 performs a comparison process between the average (=average light received) or minimum (=minimum light received) value of the received light and several threshold values. The comparison process in this step has already been explained in Figures 13 and 14 above. Therefore, a redundant explanation will be omitted.

[0148] In the following step S7, the illumination state (display pattern) of indicator lights 140 and 240 is updated according to the comparison result obtained in step S6. The flow then returns to step S1, and the above series of processes is repeated.

[0149] This diagram is drawn with the understanding that in step S6, a comparison process may be performed between the average value of the received light (=average received light) and multiple thresholds. In other words, the comparison process in step S6 is not performed for each optical axis, but rather after the received light for all optical axes has been recorded.

[0150] However, if a comparison process is performed between the minimum light-receiving amount (= minimum light-receiving amount) and multiple thresholds, step S5 may be omitted. In other words, the comparison process in step S6 may be performed sequentially for each optical axis without waiting for the light-receiving amounts of all optical axes to be recorded.

[0151] For example, if the amount of light received by the first light-receiving element 261 is below the second threshold, it is sufficient to switch to a single green light (i.e., only the indicator light source 170a is lit green) without comparing the amount of light received by each of the other light-receiving elements 262 to 266 with the threshold (see Figure 14). Therefore, subsequent comparison processing can be omitted.

[0152] <Summary> In Figures 9 to 18 above, we proposed a light curtain 1 equipped with a function to switch display patterns according to the light intensity of the optical bearing. To briefly describe this configuration, "In order to form multiple optical axes spaced apart from each other, one of the pair of light-emitting and light-receiving elements forming the multiple optical axes is arranged inside along the longitudinal direction, and the housing has a metal case extending in the longitudinal direction and end members connected to both ends of the metal case, respectively." A cover that transmits light from the light-emitting element and is attached to the housing so as to intersect with the plurality of optical axes, An indicator light, which is a light-diffusing member, is positioned outward along the longitudinal direction from at least one of the outer surfaces of the cover and the housing, or is formed in series with the cover. The enclosure comprises a light source for an indicator light, which is housed inside the enclosure and supplies light for displaying to the indicator light, The light source for the indicator light is controlled to turn on and off in a color corresponding to the operating state of the light curtain and in a display pattern corresponding to the amount of light received by the light receiving element when the light curtain is set to operation indicator light mode.

[0153] <Cascading> Figure 19 shows an example of a cascade connection. The multi-axis photoelectric sensor 1X in this figure includes multiple light curtains 1(1) to 1(3). Each light curtain 1(1) to 1(3) has a light emitter 100(1) to 100(3) and a light receiver 200(1) to 200(3). The light receivers 200(1) to 200(3) are positioned opposite the light emitters 100(1) to 100(3).

[0154] Between light curtains 1(1) to 1(3), adjacent floodlights 100(1) to 100(3) and light receivers 200(1) to 200(3) are connected in series. A series of light curtain groups is formed by this cascading connection.

[0155] Referring to this diagram, the first end of the floodlight 100(1) in the longitudinal direction and the controller 2 are connected via cable 120(1). The second end of the floodlight 100(1) in the longitudinal direction and the first end of the floodlight 100(2) in the longitudinal direction are connected via cable 120(2). The second end of the floodlight 100(2) in the longitudinal direction and the first end of the floodlight 100(3) in the longitudinal direction are connected via cable 120(3).

[0156] The first end of the light receiver 200(1) in the longitudinal direction is wired to the controller 2 via cable 220(1). The second end of the light receiver 200(1) in the longitudinal direction is wired to the first end of the light receiver 200(2) in the longitudinal direction via cable 220(2). The second end of the light receiver 200(2) in the longitudinal direction is wired to the first end of the light receiver 200(3) in the longitudinal direction via cable 220(3).

[0157] Furthermore, multiple optical axis Oax can be formed between the light emitters 100(1) to 100(3) and the light receivers 200(1) to 200(3). The multi-optical-axis photoelectric sensor 1X outputs a safety signal, i.e., the aforementioned OSSD output, to the controller 2 based on whether each of the multiple optical axis Oax is in a light-shielding state or not.

[0158] Figure 20 shows the functional block diagrams of light curtains 1(1) and 1(2) connected in series with each other. For the sake of explanation, the number of series stages in the cascade connection is assumed to be 2.

[0159] Each of the floodlights 100(1) and 100(2) comprises a plurality of light-emitting elements 160, a control circuit 181, a communication circuit 182, and connectors T11 and T12, respectively.

[0160] Each of the multiple light-emitting elements 160 sequentially emits a light beam in a time-division manner to form the optical axis Oax based on a light emission control signal input from the control circuit 181. The multiple light-emitting elements 160 can be understood as optical elements corresponding to the previously mentioned light-emitting elements 161 to 166.

[0161] The control circuit 181 generates a light emission control signal to sequentially drive the multiple light emission elements 160 in a time-division manner. In particular, the control circuit 181 functions as a light emission control unit that controls the light emission operation of the light emitters 100(1) and 100(2) in parallel, while staggering the light emission timing of each of the multiple light emission elements 160 provided in the light emitter 100(1) of the light curtain 1(1) and the light emission timing of each of the multiple light emission elements 160 provided in the light emitter 100(2) of the light curtain 1(2). This point will be described in detail later. The control circuit 181 also exchanges various information with the communication circuit 182.

[0162] The communication circuit 182 performs serial communication with the outside world via connectors T11 and T12, based on instructions from the control circuit 181.

[0163] Connector T11 is provided at the first end in the longitudinal direction of each of the floodlights 100(1) and 100(2). Connector T12 is provided at the second end in the longitudinal direction of each of the floodlights 100(1) and 100(2). Referring to this figure, cable 120(1) is connected between connector T11 of floodlight 100(1) and controller 2 (not shown). Cable 120(2) is connected between connector T12 of floodlight 100(1) and connector T11 of floodlight 100(2). Note that a terminal 310 may be connected to connector T12 of floodlight 100(2), which is located on the downstream side, i.e., the side furthest from controller 2 (not shown).

[0164] Connectors T11 and T12 may each be 3-pin connectors having a power terminal (VCC), a ground terminal (GND), and a communication terminal (COM). For example, 3-pin M12 connectors, which are highly versatile and have excellent dustproof and waterproof performance, may be used as connectors T11 and T12. Cables 120(1) and 120(2) may each be 3-wire cables including a power line (VCC), a ground line (GND), and a communication line (COM).

[0165] Inside the floodlights 100(1) and 100(2), the power terminals (VCC) of connectors T11 and T12 are connected to the internal power wiring. The ground terminals (GND) of connectors T11 and T12 are connected to the internal ground wiring. The communication terminals (COM) of connectors T11 and T12 are connected to the communication circuit 182.

[0166] Furthermore, if compliance with a differential serial communication standard, such as the RS485 standard, is required, a two-core communication line (RS485(+) / RS485(-)) may be used instead of a single-core communication line (COM). Even in this case, four pins are sufficient for both connectors T11 and T12. Therefore, highly versatile 4-pin or 5-pin M12 connectors can be used for connectors T11 and T12.

[0167] On the other hand, the light receivers 200(1) and 200(2) each include a plurality of light-receiving elements 260, a control circuit 281, a communication circuit 282, an output circuit 283, an input circuit 284, and connectors T21 and T22.

[0168] Each of the multiple photodetectors 260 sequentially receives a light beam in a time-division manner to form the optical axis Oax based on a light detection control signal input from the control circuit 281. The multiple photodetectors 260 can be understood as optical elements corresponding to the previously mentioned photodetectors 261 to 266.

[0169] The control circuit 281 generates a light receiving control signal to sequentially activate multiple light receiving elements 260 in a time-division manner, synchronized with the drive timing of each of the multiple light-emitting elements 160. In particular, the control circuit 281 functions as a light receiving control unit that controls the light receiving operation of each of the light receiving elements 200(1) and 200(2) according to the light-emitting operation of each of the light-emitting elements 100(1) and 100(2). This point will be described in detail later. The control circuit 281 also exchanges various information with the communication circuit 282, the output circuit 283, and the input circuit 284.

[0170] The communication circuit 282 performs serial communication with the outside world via connectors T21 and T22, based on instructions from the control circuit 281.

[0171] The output circuit 283 outputs safety signals OSSD1 and OSSD2 externally via connector T21, based on instructions from the control circuit 281. Note that safety signals OSSD1 and OSSD2 can be understood as multiplexed signals to enhance redundancy.

[0172] The input circuit 284 receives safety signals OSSD1 and OSSD2, which are input externally via connector T22, and transmits them to the control circuit 281.

[0173] Connector T21 is provided at the first end in the longitudinal direction of each of the light receivers 200(1) and 200(2). Connector T22 is provided at the second end in the longitudinal direction of each of the light receivers 200(1) and 200(2). Referring to this figure, cable 220(1) is connected between connector T21 of light receiver 200(1) and controller 2 (not shown). Cable 220(2) is connected between connector T22 of light receiver 200(1) and connector T21 of light receiver 200(2). A terminator 320 may be connected to connector T22 of light receiver 200(2), which is located at the downstream end.

[0174] In the light receivers 200(1) and 200(2), the novel light emission control employed in the light emitters 100(1) and 200(2) (see Figure 21 below; details will be provided later) eliminates the need for precise timing adjustments. Therefore, the light receivers 200(1) and 200(2) do not need to perform two-core differential transmission; single-core single-ended transmission is sufficient.

[0175] Therefore, connectors T21 and T22 each only need five pins: a power terminal (VCC), a ground terminal (GND), a communication terminal (COM), and safety signal terminals (OSSD1 / OSSD2). For example, 5-pin M12 connectors, which are highly versatile and have excellent dustproof and waterproof performance, can be used as connectors T21 and T22. Also, cables 220(1) and (2) may each be 5-wire cables including a power line (VCC), a ground line (GND), and safety signal lines (OSSD1 / OSSD2).

[0176] Inside the light receivers 200(1) and 200(2), the power terminals (VCC) of connectors T21 and T22 are connected to the internal power wiring. The ground terminals (GND) of connectors T21 and T22 are connected to the internal ground wiring. The communication terminals (COM) of connectors T21 and T22 are connected to the communication circuit 282. The safety signal terminals (OSSD1 / OSSD2) of connector T21 are connected to the output circuit 283. The safety signal terminals (OSSD1 / OSSD2) of connector T22 are connected to the input circuit 284.

[0177] Thus, the light emitter 100(1) and the light receiver 200(1) are connected between the controller 2 (not shown) and the light emitter 100(2) and the light receiver 200(2), respectively. In other words, with respect to the controller 2 (not shown), the light emitter 100(1) and the light receiver 200(1) are located on the upstream side, and the light emitter 100(2) and the light receiver 200(2) are located on the downstream side.

[0178] In this case, safety signals OSSD1 and OSSD2 are transmitted from receiver 200(2) to receiver 200(1), and then from receiver 200(1) to controller 2 (not shown). This method of signal transmission is sometimes called an OSSD cascade.

[0179] In order to clearly distinguish between the safety signals OSSD1 and OSSD2 generated by receiver 200(1) and the safety signals OSSD1 and OSSD2 generated by receiver 200(2), in the following explanation, the former may be referred to as safety signal OSSD(1) and the latter as safety signal OSSD(2).

[0180] For example, the control circuit 281 of the light receiver 200(2) generates a safety signal OSSD(2) based on the light-ingress / obstruction state of each of the multiple optical axis Oax formed between the light emitter 100(2) and the light receiver 200(2), in other words, whether each of the multiple optical axis Oax is in an obstruction state or not. Therefore, the safety signal OSSD(2) reflects only the optical axis detection state of the light curtain 1(2). For example, the safety signal OSSD(2) may be turned ON when all of the multiple optical axis Oax are in an ingress state at the light receiver 200(2). The control circuit 281 of the light receiver 200(2) transmits the safety signal OSSD(2) to the light receiver 200(1).

[0181] The control circuit 281 of the light receiver 200(1) generates a safety signal OSSD(1) based on the light input / blocking state of each of the multiple optical axes Oax formed between the light emitter 100(1) and the light receiver 200(1), and the safety signal OSSD(2) received from the light receiver 200(2). Therefore, the safety signal OSSD(1) is the result of aggregating and reflecting the optical axis detection state of both the light curtains 1(1) and 1(2).

[0182] For example, the control circuit 281 of the light receiver 200(1) may generate the safety signal OSSD(1) by performing a logical AND operation between the light-ingress / light-blocking state of the light receiver 200(1) and the safety signal OSSD(2). In this case, the safety signal OSSD(1) is turned ON when it is detected that all optical axis Oax are in the light-ingress state in both the light receivers 200(1) and 200(2). The control circuit 281 of the light receiver 200(1) transmits the safety signal OSSD(1) to a controller 2 (not shown).

[0183] According to the above series of OSSD cascades, it is possible to inform the controller 2 (not shown) of the optical axis detection results of both light curtains 1(1) and 1(2) without increasing the number of safety signal lines (OSSD1 / OSSD2).

[0184] If reducing the number of pins in connectors T21 and T22 is prioritized, safety signals OSSD(1) and OSSD(2) may be transmitted via communication circuit 282, respectively.

[0185] <Floodlight control> Figure 21 shows the old and new light projection control for the multi-optical axis photoelectric sensor 1X. The upper left column schematically shows the optical axis formation process using the conventional light projection control. The upper right column schematically shows the light projection timing using the conventional light projection control. The lower left column schematically shows the optical axis formation process using the new light projection control. The lower right column schematically shows the light projection timing using the new light projection control. In this figure, light curtain 1(1) has 4 optical axes, and light curtain 1(2) has 7 optical axes.

[0186] As shown in the upper part of this figure, in conventional light projection control, an optical axis scan is first performed from the leading optical axis [1] to the trailing optical axis [4] of the light projector 100(1). Then, the optical axis scan is continued from the leading optical axis [5] to the trailing optical axis

[11] of the light projector 100(2). In other words, the light emission / reception operation is performed sequentially, one optical axis at a time, from the leading optical axis [1] of the light projector 100(1) to the trailing optical axis

[11] of the light projector 100(2). The above operation is repeated thereafter.

[0187] In other words, in conventional light projection control, a first optical axis scan period SCAN(1) sequentially detects whether each of the multiple optical axes [1] to [4] formed by the light curtain 1(1) is in a light-shielding state, and a second optical axis scan period SCAN(2) sequentially detects whether each of the multiple optical axes [5] to

[11] formed by the light curtain 1(2) is in a light-shielding state, and these are set in series on the time axis.

[0188] In conventional light control systems, floodlights 100(1) and 100(2) operate in series as a single unit. Therefore, mutual light interference between adjacent light curtains 1(1) and 1(2) is less likely to occur. However, conventional light control systems have a reduced response speed for OSSD output and require precise timing adjustments.

[0189] On the other hand, as shown in the lower part of this figure, in the novel light projection control, a first optical axis scan period SCAN(1) sequentially detects whether or not each of the multiple optical axes [1] to [4] formed by the light curtain 1(1) is in a light-shielding state, and a second optical axis scan period SCAN(2) sequentially detects whether or not each of the multiple optical axes [1] to [7] formed by the light curtain 1(2) is in a light-shielding state, are set in parallel on the time axis.

[0190] In other words, the first optical axis scan period SCAN(1) is repeated in light curtain 1(1). On the other hand, the second optical axis scan period SCAN(1) is repeated in light curtain 1(2).

[0191] Thus, with this novel light projection control, the series-connected light curtains 1(1) and 1(2) can each perform optical axis detection independently, just as they would when used individually. Therefore, the response speed of the OSSD output is less likely to decrease compared to conventional light projection control. Furthermore, precise timing adjustments become unnecessary.

[0192] Furthermore, the light transmission and reception timings of the light curtains 1(1) and 1(2) are staggered. For example, the light receivers 200(1) and 200(2) may switch the active / inactive state of the light receiving element 260 in synchronization with the light transmission timings of the light emitters 100(1) and 100(2). Alternatively, the light receivers 200(1) and 200(2) may ignore incoming light information that is outside the light transmission timings of the light emitters 100(1) and 100(2). With this configuration, mutual light interference between the light curtains 1(1) and 1(2) can also be suppressed.

[0193] Figure 22 shows the activation flow for each of the floodlights 100(1) to 100(M). Here, M is a natural number greater than or equal to 2.

[0194] When the startup flow shown in this figure begins, in step S11, the light emitters 100(1) to 100(M) first recognize their series connection status, for example, which light emitter they are in series with the multi-axis photoelectric sensor 1X, through communication. This communication can be performed via the communication circuit 182.

[0195] Next, in step S12, the Nth floodlight 100(N) transmits its own reference pulse CLK(N) to the N+1th floodlight 100(N+1). The reference pulse CLK(N) may be a pulse signal with a predetermined period t. The reference pulse CLK(N) can be transmitted via the aforementioned communication circuit 182, where N is a natural number between 1 and M-1.

[0196] Subsequently, in step S13, the (N+1)th light emitter 100(N+1) receives the reference pulse CLK(N). Light emitter 100(N+1) also generates its own reference pulse CLK(N+1) by shifting the phase of the reference pulse CLK(N). The amount of phase shift may be, for example, 1 / n of the period t, where n is a real number greater than 1. Note that n can basically be a natural number. Of course, n is not necessarily limited to a natural number as long as the effect of offsetting by the amount of time without interference can be obtained. After receiving the reference pulse CLK(N), light emitter 100(N+1) may return a response to light emitter 100(N).

[0197] Furthermore, each of the light emitters 100(1) to 100(M) may be equipped with its own oscillator that operates asynchronously with respect to the others. In that case, the light emitter 100(1) located at the uppermost position may use the pulse signal with period t generated by its own oscillator as the reference pulse CLK(1). In contrast, the light emitters 100(K) from the second stage onward may generate a reference pulse CLK(K) by delaying the pulse signal with period t generated by its own oscillator, thereby shifting the phase of the reference pulse CLK(K-1) received from light emitter 100(K-1) by t / n. Hereinafter, K is a natural number between 2 and M.

[0198] In this configuration, after the timing adjustment of each reference pulse CLK(1) to CLK(M) is completed in the startup flow shown in this figure, the generation of reference pulses CLK(1) to CLK(M) continues independently by each of the light emitters 100(1) to 100(M). In other words, it is not necessary to continuously transmit the reference pulse CLK(N) from the upstream side to the downstream side between the light emitters 100(1) to 100(M). Therefore, the communication load of the communication circuit 182 can be reduced. Note that the timing adjustment of each reference pulse CLK(1) to CLK(M) may be performed again periodically.

[0199] If the transmission and reception of the reference pulse CLK(N) and the phase shift described above are completed up to the terminal equipment, i.e., the downstream light emitter 100(M), then the branch in step S14 will result in a "yes" determination, and the flow will proceed to step S15.

[0200] On the other hand, if the branch in step S14 results in a "no" judgment, N is incremented by one, and the flow returns to step S12. Thus, the transmission and reception of the reference pulse CLK(N) and the phase shift are sequentially repeated from the first to the second, then from the second to the third, and so on, from the upstream floodlight 100(1) to the downstream floodlight 100(M).

[0201] In step S15, the light emitters 100(1) to 100(M) start emitting light in synchronization with their respective reference pulses CLK(1) to CLK(M). At this time, each light emitter 100(1) to 100(M) emits light on the optical axis assigned for timing synchronization among the multiple optical axes Oax, using its own unique synchronization pulse pattern. The synchronization pulse pattern of each light emitter 100(1) to 100(M) may be a pulse pattern corresponding to which light emitter 100(1) to 100(M) is in the multi-optical-axis photoelectric sensor 1X.

[0202] Figure 23 shows the activation flow for each of the photodetectors 200(1) to 200(M), where M is a natural number.

[0203] When the startup flow shown in this figure begins, in step S21, the photodetectors 200(1) to 200(M) first recognize their series connection status, for example, which number each photodetector is connected in series within the multi-axis photoelectric sensor 1X, through communication. This communication can be performed via the communication circuit 282.

[0204] Next, in step S22, each of the light receivers 200(1) to 200(M) establishes synchronization with each of the light emitters 100(1) to 100(M) by detecting the reception of their respective synchronization pulse patterns. The synchronization pulse patterns that each of the light receivers 200(1) to 200(M) awaits to receive may be pulse patterns corresponding to which light receiver 200(1) to 200(M) is in the multi-axis photoelectric sensor 1X. More specifically, the synchronization pulse patterns that each of the light receivers 200(1) to 200(M) awaits to receive may be the synchronization pulse patterns emitted by each of the light emitters 100(1) to 100(M). In other words, each of the light receivers 200(1) to 200(M) only synchronizes with its corresponding light emitter 100(1) to 100(M).

[0205] In this way, the light transmission and reception timings between the light emitters 100(1) to 100(M) and the light receivers 200(1) to 200(M) are synchronized using a so-called optical synchronization method. Therefore, wiring work between the light emitters 100(1) to (M) and the light receivers 200(1) to (M) is unnecessary, thus increasing the flexibility of the wiring.

[0206] <Phase shift> Figure 24 shows a first example of the phase shift (2 series, 1 / 2 period shift) performed in step S13 of Figure 22. The upper part of this figure shows the light emission timing of floodlight 100(1). The lower part of this figure shows the light emission timing of floodlight 100(2).

[0207] As described above, the light emitter 100(1) operates in synchronization with the reference pulse CLK(1) with period t. Therefore, in the first optical axis scan period SCAN(1), multiple light emission timings for optical axes [1] to [4] are set for each period t. In addition, the first interval period INT(1), which is provided between the completion of the first optical axis scan period SCAN(1) and the start of the next first optical axis scan period SCAN(1), is also set to have the same length as period t.

[0208] On the other hand, the light emitter 100(2) performs its light emission operation in synchronization with a reference pulse CLK(2) with period t. Therefore, in the second optical axis scan period SCAN(2), multiple light emission timings for optical axes [1] to [7] are set for each period t. In addition, the second interval period INT(2), which is provided between the completion of the second optical axis scan period SCAN(2) and the start of the next second optical axis scan period SCAN(2), is also set to have the same length as period t.

[0209] As mentioned earlier, the reference pulse CLK(2) is generated by shifting the phase of the reference pulse CLK(1) by 1 / n of the period t. Referring to this figure, the reference pulse CLK(2) is shifted in phase by t / 2 relative to the reference pulse CLK(1).

[0210] In other words, the series-connected light emitters 100(1) and 100(2) emit light at the same period t, while shifting their respective emission timings by t / 2, regardless of the number of optical axes of each. With this type of emission control, mutual optical interference between the light curtains 1(1) and 1(2), which perform optical axis detection independently, can be suppressed.

[0211] Figure 25 shows a second example of phase shift (3 series, 1 / 2 period shift). The upper part of this figure shows the illumination timing of floodlight 100(1). The middle part of this figure shows the illumination timing of floodlight 100(2). The lower part of this figure shows the illumination timing of floodlight 100(3).

[0212] As shown in this figure, when floodlights 100(1) to 100(3) are connected in series, and their respective illumination timings are shifted by t / 2, the illumination timing of floodlight 100(1) and floodlight 100(3) will coincide.

[0213] However, floodlight 100(2) is interposed between floodlight 100(1) and floodlight 100(3). Therefore, for example, if floodlights 100(1) to 100(3) are arranged in a line, floodlights 100(1) and 100(3) will not be adjacent to each other. In this case, the mutual optical interference between floodlights 100(1) and 100(3) does not need to be considered to a great extent.

[0214] Therefore, as shown in this figure, if the light emission timings between the light emitters 100(1) and 100(2), and between the light emitters 100(2) and 100(3), mutual light interference can be sufficiently suppressed.

[0215] Figure 26 shows a third example of phase shift (3 series, 1 / 3 period shift). Similar to Figure 25, the upper part of this figure shows the illumination timing of floodlight 100(1). The middle part of this figure shows the illumination timing of floodlight 100(2). The lower part of this figure shows the illumination timing of floodlight 100(3).

[0216] As shown in this figure, when floodlights 100(1) to 100(3) are connected in series, if their respective emission timings are shifted by t / 3, the emission timings of floodlights 100(1) to 100(3) will all be mismatched. Therefore, even if floodlights 100(1) and 100(3) are adjacent to each other, mutual optical interference can be suppressed.

[0217] Furthermore, in order to enhance the effect of suppressing optical interference, the period t may be extended in proportion to the increase in the denominator n, so that the phase shift amount t / n does not become too small. However, it is desirable that the period t be set so that the response times of each light curtain 1(1) to 1(3) fall within an acceptable range.

[0218] <Interference prevention settings> Incidentally, some light curtains using the optical synchronization method have an interference prevention setting (A / B) as a means of preventing mis-synchronization or malfunction between adjacent light curtains. For example, by using a 2-bit 4-value DIP switch, settings such as "00 (interference prevention setting off)", "01 (setting A)", and "10 (setting B)" are possible.

[0219] Figure 27 shows an example of interference prevention settings. As shown in this figure, the light emitter in setting A performs multiple light emission operations per optical axis with a unique pulse pattern. For example, when detecting the light-ingress / blocking state of an optical axis, the light emitter in setting A emits multiple light emission pulses (e.g., 3 pulses) at a predetermined frequency fA. The light receiver in setting A determines whether the optical axis is in an enabled or blocked state based on its light-receiving operation, depending on whether it has detected the reception of a pulse pattern unique to setting A. For example, the light receiver in setting A determines that the optical axis is in an enabled state when a majority (e.g., 2 or more) of the light pulses are detected at frequency fA.

[0220] On the other hand, the light emitter in setting B performs multiple light emission operations per optical axis with a unique pulse pattern different from that of the light emitter in setting A. For example, when detecting the light-in / light-out state of a single optical axis, the light emitter in setting B emits multiple light emission pulses (e.g., 3 pulses) at a frequency fB that is different from frequency fA. The light receiver in setting B determines whether the optical axis is in a light-in or light-out state based on its light-receiving operation, depending on whether it has detected the reception of a pulse pattern unique to setting B. For example, the light receiver in setting B determines that the optical axis is in a light-in state when a majority (e.g., 2 or more pulses) of the light emission pulses are detected at frequency fB.

[0221] Thus, the light curtains in setting A and setting B transmit and receive light at their respective frequencies fA and fB, and more broadly, with their respective pulse patterns. Therefore, even if a light pulse emitted from the light curtain in setting A is detected by the light curtain in setting B, the difference in pulse patterns can prevent mis-synchronization or malfunction. Conversely, the same applies if a light pulse emitted from the light curtain in setting B is detected by the light curtain in setting A.

[0222] However, when constructing the aforementioned multi-axis photoelectric sensor 1X using a light curtain with interference prevention settings, optical interference between multiple multi-axis photoelectric sensors must be considered. This point will be explained below.

[0223] <Optical interference between multiple multi-axis photoelectric sensors> Figure 28 shows an example of optical interference between multiple multi-axis photoelectric sensors.

[0224] The multi-axis photoelectric sensor 1A has light curtains 1A(1) and 1A(2). Light curtain 1A(1) has a light emitter 100A(1) and a light receiver 200A(1) opposite it. Light curtain 1A(2) has a light emitter 100A(2) and a light receiver 200A(2) opposite it. Between light curtains 1A(1) and 1A(2), adjacent light emitters 100A(1) and 100A(2), and light receivers 200A(1) and 200A(2) are connected in series.

[0225] The multi-axis photoelectric sensor 1B has light curtains 1B(1) and 1B(2). Light curtain 1B(1) has a light emitter 100B(1) and a light receiver 200B(1) opposite it. Light curtain 1B(2) has a light emitter 100B(2) and a light receiver 200B(2) opposite it. Between light curtains 1B(1) and 1B(2), adjacent light emitters 100B(1) and 100B(2), and light receivers 200B(1) and 200B(2) are connected in series.

[0226] The multi-axis photoelectric sensors 1A and 1B can be understood as the previously described multi-axis photoelectric sensor 1X, respectively. That is, the light emitters 100A(1) and 100A(2), and the light emitters 100B(1) and 100B(2), respectively correspond to the previously described light emitters 100(1) and 100(2). Similarly, the light receivers 200A(1) and 200A(2), and the light receivers 200B(1) and 200B(2), respectively correspond to the previously described light receivers 200(1) and 200(2).

[0227] The multi-axis photoelectric sensors 1A and 1B operate asynchronously with respect to each other. Furthermore, the light curtains 1A(1) and 1A(2) are driven in parallel with each other. Similarly, the light curtains 1B(1) and 1B(2) are also driven in parallel with each other. Therefore, for example, as shown in this figure, light pulses emitted from a total of three units—light emitters 100A(1) and 100A(2) and light emitter 100B(1)—can be incident on a single light receiver 200B(1) simultaneously or nearly simultaneously.

[0228] Therefore, in the worst case, the light receiver 200B(1) may detect multiple light pulses at timings corresponding to the aforementioned frequencies fA or fB. Considering this situation, it is difficult to apply the interference prevention settings (A / B) shown in Figure 27 to each of the light curtains 1A(1) and 1A(2), as well as light curtains 1B(1) and 1B(2).

[0229] Furthermore, by setting the aforementioned period t to an extremely long value, it is not impossible to achieve parallel driving of light curtains 1A(1) and 1A(2), as well as parallel driving of light curtains 1B(1) and 1B(2), and to achieve both interference prevention settings (A / B). However, with such settings, the response time of the OSSD output becomes significantly longer, so it cannot be considered a practical solution.

[0230] Therefore, when the interference prevention setting is enabled for light curtains 1A(1) and 1A(2), and light curtains 1B(1) and 1B(2), for example, when the DIP switch is set to "01 (setting A)" or "10 (setting B)", an error display may be made using the indicator lights 140 and 240 mentioned earlier. Such an error display makes it possible to make the operator aware that the interference prevention setting is not possible.

[0231] Furthermore, in conjunction with the prohibition of enabling the interference prevention setting (A / B), it is desirable that optical interference between the multi-axis photoelectric sensors 1A and 1B be suppressed by other countermeasures, such as modifications to the installation.

[0232] Furthermore, the multi-axis photoelectric sensors 1A and 1B may be designed to allow switching between the old and new light projection control methods shown in Figure 21. For example, the light curtains 1A(1) and 1A(2), and the light curtains 1B(1) and 1B(2) may each have a first operating mode that performs the new light projection control (lower part of Figure 21), as well as a second operating mode that performs the conventional light projection control (upper part of Figure 21). In the second operating mode, unlike the first operating mode, the interference prevention setting (A / B) can be enabled.

[0233] Therefore, if the configuration allows for the selection of either the first or second operating mode, the multi-axis photoelectric sensors 1A and 1B can be flexibly operated according to the user's specifications, specifically depending on whether to prioritize improved response speed or interference prevention.

[0234] <Other variations> Furthermore, the various technical features disclosed herein can be modified in various ways, in addition to the embodiments described above, without departing from the spirit of the technical creation. In other words, the embodiments described above should be considered in all respects to be illustrative and not restrictive, and the technical scope of the present invention should be defined by the claims and understood to include all modifications that fall within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0235] 1, 1(1), 1(2), 1(3), 1A(1), 1A(2), 1B(1), 1B(2) Light Curtain 1X, 1A, 1B Multi-Axis Photoelectric Sensor 2 Controllers 100, 100(1), 100(2), 100(3), 100A(1), 100A(2), 100B(1), 100B(2) Floodlights 200, 200(1), 200(2), 200(3), 200A(1), 200A(2), 200B(1), 200B(2) Receiver 110, 210 cabinets 111, 211 Metal Case 111a Main Unit 111b 1st protruding strip 111c 2nd protruding strip 112, 113, 212, 213 End caps (end members) 120, 120(1), 120(2), 120(3) Cables 220, 220(1), 220(2), 220(3) Cables 130 Front Cover 140, 240 indicator light 150 Bumper section 160, 161-166 Light-emitting elements 260, 261-266 Photodetector 170, 170a / b / c, 270, 270a / b / c light source for indicator light 181, 281 Control circuits 182, 282 Communication Circuits 284 Input Circuit 283 Output Circuit 190, 190x, 190y, 190z circuit board 190a central area 190b End area 191 Light-shielding plate 310, 320 terminator Oax1~Oax6 Optical axis T11, T12, T21, T22 connectors X-axis intersection area

Claims

1. A multi-optical-axis photoelectric sensor comprising a plurality of light curtains, each having a light emitter equipped with a plurality of light-emitting elements and a light receiver equipped with a plurality of light-receiving elements that receive light emitted from the plurality of light-emitting elements, wherein a series of light curtain groups is formed by connecting the light emitters in series with each other and the light receivers with each other between one light curtain and another light curtain, A light projection control unit controls the light projection operation of the first and second light projection units in parallel, while shifting the light projection timing of the multiple first light projection elements provided in the first light projection unit of the first light projection unit of the first light projection unit of the first light projection unit of the first light projection unit of the first light projection unit of the first light projection unit of the first light projection unit of the second light projection unit of the other light projection unit of the second light projection unit of the other light projection unit. A light receiving control unit controls the light receiving operation of the first light receiver of one light curtain and the second light receiver of the other light curtain in accordance with the light emission operation of the first light receiver and the second light receiver, respectively. An output circuit that outputs a safety signal to the outside, generated based on whether or not the multiple optical axes formed between the first light emitter and the first light receiver and between the second light emitter and the second light receiver are in a light-shielding state, A multi-optical-axis photoelectric sensor equipped with the following features.

2. The multi-optical-axis photoelectric sensor according to claim 1, wherein the first light emitter and the first light receiver are connected between the controller and the second light emitter and the second light receiver, respectively.

3. The multi-axis photoelectric sensor according to claim 2, wherein the first light emitter and the second light emitter each recognize which light emitter is connected in series with the multi-axis photoelectric sensor and perform light emission operation of the optically synchronized optical axis with a unique synchronization pulse pattern, and the first light receiver and the second light receiver each recognize which light receiver is connected in series with respect to the controller and establish synchronization with the first light emitter and the second light emitter by detecting the reception of the synchronization pulse pattern.

4. The multi-optical-axis photoelectric sensor according to claim 3, wherein the first light emitter sets the emission timing of the first light emitter in synchronization with a first reference pulse and transmits the first reference pulse to the second light emitter, and the second light emitter generates a second reference pulse with the same period as the first reference pulse received from the first light emitter but with the phase shifted by an offset amount, and sets the emission timing of the second light emitter in synchronization with the second reference pulse.

5. The multi-optical-axis photoelectric sensor according to claim 4, wherein the offset amount is 1 / n of the period, and n is a real number greater than 1.

6. The multi-optical-axis photoelectric sensor according to claim 2, wherein the second light receiver generates a second safety signal based on the light-ingress / light-blocking state of each of the multiple optical axes formed between the second light emitter and the second light receiver, and transmits the second safety signal to the first light receiver, and the first light receiver generates a first safety signal based on the light-ingress / light-blocking state of each of the multiple optical axes formed between the first light emitter and the first light receiver and the second safety signal received from the second light receiver.

7. The multi-optical-axis photoelectric sensor according to claim 6, wherein the first and second photodetectors each have a 5-pin connector.

8. A multi-optical-axis photoelectric sensor according to any one of claims 1 to 7, comprising a first operating mode in which a first optical axis scan period for sequentially detecting whether each of the multiple optical axes formed by the first light curtain is in a light-shielding state and a second optical axis scan period for sequentially detecting whether each of the multiple optical axes formed by the other light curtain is in a light-shielding state are set in parallel.

9. The multi-optical-axis photoelectric sensor according to claim 8, further comprising a second operating mode in which the first optical axis scan period and the second optical axis scan period are set in series, wherein one of the first operating mode and the second operating mode is selected.

10. The multi-optical-axis photoelectric sensor according to claim 9, wherein in the second operating mode, the first light emitter and the second light emitter each perform multiple light emission operations per optical axis with a unique pulse pattern, and the first light receiver and the second light receiver determine whether the optical axis is in a light-shielding state depending on whether or not they have detected the reception of the pulse pattern by their respective light-receiving operations.

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