Photoelectric sensor and emitting device for photoelectric sensor

A purpose of the present invention is to provide a photoelectric sensor and an emitting device for a photoelectric sensor which can improve resistance to liquids. A purpose of the present invention is also to provide a photoelectric sensor and an emitting device for a photoelectric sensor which can improve productivity.According to the present invention, a main casing is described in which a plurality of photoelectric elements are included along a first direction; a first opening formed on the main casing for passing through a light corresponding to the photoelectric element between the inside and outside of the main casing; a transparent plate affixed on a pair of first surfaces of the main casing so as to cover the first opening, for passing through the light between the inside and outside of the main casing; a first adhesive member disposed between the transparent plate and the pair of first surfaces, for affixing the transparent plate on the pair of first surfaces; a pair of projections formed on the main casing along the first direction, outstanding along to an optical axis of the light, and disposed apart from each other whereby the transparent plate is accessible from the outside of the main casing to the pair of first surfaces; a pair of channels formed on the main casing along the first direction and between the pair of first surfaces and the pair of projections of the main casing; and a pair of first pressing members fixed in the pair of channels and contacting an opposite side of the surface where the transparent plate is located, for pressing the transparent plate to the main casing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2007-171666, filed on Jun. 29, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric sensor and an emitting device for the photoelectric sensor. More particularly, the present invention relates to an improvement in structure of a photoelectric sensor having a transparent plate for passing through detection light and a casing holding an optical element irradiating or receiving the detection light, such as a photoelectric element or an emitting element.

2. Description of Related Art

Some photoelectric sensors have an optical element such as a photoelectric element and an emitting element; a main casing holding the optical element; a transparent plate coupled to the main casing; and for passing through a light related to the optical element. Japanese Laid-Open Patent No. 2001-155597 shows a structure for affixing the transparent plate to the main casing with a slide action.

According to conventional technology shown in the Japanese Laid-Open Patent, a sealing member such as a gasket is not installed between the main casing and the transparent plate which can slide on the main casing so as to be affixed on the main casing. Therefore, liquid, i.e. water and oil, is likely to leak in the main casing through a gap between the main casing and the transparent plate. The leakage is likely to damage the sensor.

For example, in the case where the sensors are installed in a product line, oil utilized in a processing machine may spread on the sensors. Then, the oil is likely to leak into the sensors. If the sensors installed in the product line fail due to the leakage of the oil, the operation of the product line is generally suspended until the failed sensors are replaced. This suspended time of the product line causes lower productivity. Moreover, even though the suspended time may be short, safety confirmation for restarting the product line may take a longer time. Thus, suspension of the product line causes reducing productivity.

Ring gaskets might be installed at the surroundings of the openings which are covered by a transparent plate so as to avoid leaking of liquid inside of the sensor. However, since the opening shape depends on the size of the sensor, various sizes of gaskets should be prepared in accordance with the size of the sensor. In the case of a multi-axis photoelectric sensor, the sensor should be prepared for various detection lengths so as to comply with various applications. So, in situation, the main casings of the sensors are made by cutting longitudinal pipe to desirable length. In this manner, it's easy to produce sensors having various detection lengths. But since the shape of the gasket is a ring, the above manner can not be adapted for producing the ring gaskets. Therefore, various sizes of ring gaskets should be prepared corresponding to the desire lengths of the main casings. Consequently, productivity is reduced.

One might consider using adhesive tape that is bonded along the opening instead of the gasket where a transparent plate is held by the adhesive tape. However, it may be difficult to place the adhesive tape between the main casing and the transparent plate because of the structure for sliding the transparent plate on the main casing to unit each other.

SUMMARY OF THE INVENTION

The above-described problems associated with the prior art photoelectric sensor are believed solved by the present invention. Specially, a purpose of the present invention is to provide a photoelectric sensor and an emitting device for a photoelectric sensor which can improve resistance to liquids. A purpose of the present invention is also to provide a photoelectric sensor and an emitting device for a photoelectric sensor which can improve productivity.

According to the present invention, a main casing is described in which a plurality of photoelectric elements are included along a first direction;

a first opening formed on the main casing for passing through a light corresponding to the photoelectric element between the inside and outside of the main casing;

a transparent plate affixed on a pair of first surfaces of the main casing so as to cover the first opening, for passing through the light between the inside and outside of the main casing;

a first adhesive member disposed between the transparent plate and the pair of first surfaces, for affixing the transparent plate on the pair of first surfaces;

a pair of projections formed on the main casing along the first direction, outstanding along to an optical axis of the light, and disposed apart from each other whereby the transparent plate is accessible from the outside of the main casing to the pair of first surfaces;

a pair of channels formed on the main casing along the first direction and between the pair of first surfaces and the pair of projections of the main casing; and

a pair of first pressing members fixed in the pair of channels and contacting an opposite side of the surface where the transparent plate is located, for pressing the transparent plate to the main casing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a perspective view of a photoelectric sensor1according to this embodiment.FIG. 2shows a perspective view of the photoelectric sensor1as shown inFIG. 1from an opposite side ofFIG. 1.FIG. 3shows a side view of the photoelectric sensor1as shown inFIG. 1.FIG. 4shows a cross sectional view along the A-A line of the photoelectric sensor as shown inFIG. 3.FIG. 5shows an exploded perspective view of the photoelectric sensor1as shown inFIG. 1. In this description, directions are defined as follows except where otherwise indicated. Direction “left” is defined as left shown inFIG. 3on the basis of the attitude of the photoelectric sensor1, direction “right” is defined as right shown inFIG. 3on the basis of the attitude, direction “front” is defined as left shown inFIG. 4on the basis of the attitude, and direction “back” is defined as right shown inFIG. 4on the basis of the attitude.

The photoelectric sensor1has a main casing2elongated along a first direction and a pair of end casings3coupled to both ends of the elongated main casing2. The main casing2can be made of metal such as aluminum and can be made by using an extruder. On the other hand, the end casing3can be made of metal such as zinc alloy and can be made by die casting. In the alternative, the end casing3may be made of resin and may be made by injection molding. An optical element4such as a photoelectric element and an emitting element is installed in the main casing2and the end casings3. A single rectangular transparent plate5is coupled over the front surfaces of both the main casing2and the end casings3.

The transparent plate5can be made of glass or the like so as to allow a light related to the optical element4to pass through and between the outside and the inside of both the main casing2and the end casings3. In other word, the photoelectric element as the optical element4provides an electrical signal corresponding to the amount of receiving light which passes through the transparent plate5. On the other hand, the emitting element as the optical element4emits light to the outside of the casings through the transparent plate5. In this embodiment, a plurality of photoelectric elements as the optical elements4are arranged at regular intervals in a line along the first direction.

The photoelectric sensor1may include an emitting device in which a plurality of emitting elements as the optical element4are arranged at regular intervals in a line along the elongated direction of the main casing2, and a receiving device, which has substantially the same outline shape as the emitting device, in which a plurality of photoelectric elements as the optical element4are arranged at the regular intervals in a line along the elongated direction of the main casing2. The emitting device and the receiving device are arranged so that each of the plurality of emitting elements in the emitting device irradiates light to a detection area, and each of the plurality of photoelectric elements receives the light corresponding to each of the plurality of emitting elements from the detection area. Thus, a plurality of optical axes, namely light curtain, are formed in the detection area by the emitting device and the receiving device. Such photoelectric sensors1are so-called a multi-axis photoelectric sensor, and detect interruption of either optical axes due to existence of an object in the detection area or intrusion of an object in the detection area.

In assembling the photoelectric sensor1, the plurality of optical elements4are arranged in the main casing2, then the end casings3are coupled to both ends of the main casing2with a gasket6(referring toFIG. 5) made of an elastic material such as a rubber or an elastic polymer. In this manner, the plurality of optical elements4are installed in the inside of the photoelectric sensor1. In this embodiment, four screw holes are formed on the coupling side surfaces of the end casings3. A fastener such as a screw is inserted in each of the four holes on the respective end casing3so that respective end casing3is fixed to both ends of the main casing2.

After the main casing2and the pair of end casings3are coupled to each other in this manner, double-sided adhesive tapes7,8(referring toFIG. 5) are mounted on the front surfaces of the main casing2and the end casings3. The transparent plate5covers over the front surfaces of the main casing2and the end casing3with the double-sided adhesive tapes7,8, and then, the transparent plate5is bound to the main casing2and the end casings3. In this embodiment, the adhesive tape7mounted on the main casing2is a first adhesive member elongating from one end of the main casing2to the other in a line along the first direction, that is, along an arranging direction of the plurality of optical elements4. On the other hand, the adhesive tape8mounted on the end casings3, are a ring-shaped second adhesive member corresponding to the outer edge of the mounting surfaces of the end casings3.

A pressing member9is attached to the main casing2in order to press front surface of the transparent plate5to the back direction. The pressing member9elongates from one end of the main casing2to the other in a line along the first direction, and is formed of, for example, an elastic material such as a rubber or an elastic polymer. The pressing member9corresponds to the shape to the adhesive tape7, and is mounted on the front surface of the transparent plate5. In other words, the pressing member9is fixed so as to press the transparent plate5toward the inside of the main casing2along an optical axis of the optical element4.

On the other hand, on the end casings3, a pressing member10is attached in order to press the front surface of the transparent plate5toward the front surfaces of the end casings3. The pressing member10is a second pressing member having a ring shape which is formed along the outer edge of the front surfaces of the end casings3, and is formed of, for example, a metal plate. The pressing member10corresponds to the shape to the adhesive tape8, and the pressing member10is fixed so that the transparent plate5is mounted between the adhesive tapes8and the pressing member10.

FIG. 6shows a side view of the main casing2from one end of the elongated photoelectric sensor1.FIG. 6shows that the end casing3is coupled to the other end of the main casing2. As shown inFIG. 6, on a front surface of the main casing2, a first opening21is formed in order for the light to pass through and between the inside and outside of the main casing2. The first opening21is elongated from one end to the other end of the main casing2along the first direction. In the emitting device, the first opening21allows the light irradiated from the emitting element as the optical element4to pass through to outside of the main casing2. In the receiving device, the first opening21allows the light inputted from outside of the main casing2to pass through to the photoelectric element as the optical element4.

A pair of first mounting surfaces22is formed on both left and right sides of the first opening21in the front surface of the main casing2and is formed from one end to the other of the main casing2along the first direction, that is, on both sides of the first opening21along a direction perpendicular to both an arrangement direction of the plurality of optical elements4and the optical axis of the optical element4. Each pair of first mounting surfaces22is formed in a plane. Thus, in this manner of mounting adhesive tapes on the pair of first mounting surfaces22and mounting the transparent plate5on the adhesive tapes, the transparent plate5is affixed on the pair of first mounting surfaces22so that the transparent plate5can cover the first opening21.

Walls23projecting to the front side of the main casing2, are formed at the outer edges of the pair of first mounting surfaces22along the first direction, that is, the walls23are formed at a left edge of the left first mounting surface22and a right edge of the right first mounting surface22. The walls23are formed in parallel to each other, and a distance between the walls23corresponds to the width of the transparent plate5in the left and right direction of the main casing2. Therefore, when the transparent plate5is affixed on the pair of first mounting surfaces22via the pieces of adhesive tape7, the transparent plate5can be disposed between the walls23side by side. Therefore, the walls23can avoid shifting of the transparent plate5in the left and right direction of the main casing2.

A pair of hollow portions25and a pair of first projections26are formed at the outside of the pair of walls23by a continuous surface24including a bended part or a curved part, that is, the pair of hollow portions25and the pair of first projections26are formed at a left side of the left wall23and a right side of the right wall23. The hollow portion25is disposed at a back position relative to the first mounting surface22. The projection26projects so that the front end of the projection26reaches to the front position relative to the wall23. A groove27shaped cylinder is formed of a linear shape by the continuous surface24at each back side portion of the pair of hollows25along the first direction. At both ends of the grooves27, fasteners inserted into holes31(referring toFIG. 7) are engaged so that each end casing3is joined to the main casing2. In case where a screw is utilized as the fastener, an internal thread is formed at both ends of the grooves27.

Such grooves27do not include only two grooves27formed on a front half of the main casing2, but the grooves27also include two grooves27formed on a back half of the main casing2. In other words, at the back half of the main casing2, a hollow is formed by a continuous surface, and is depressed toward the front side. At front portions of the hollow, the grooves27have a cylindrical shape and are formed to linear shape along the first direction.

The pair of first projections26face each other in the right and left direction. Each of the pair of projections26projects toward the front side, and each front end of the pair of projections26bends to the inside at an approximate right angle and projects toward each other. In other words, each of the pair of projections26is formed to an approximate L shape. The front ends of the pair of first projection26projects toward each other and reaches up to each position corresponding to the walls23along the right and left direction. A pair of channels28is formed by each of the walls23and each front end of the projections26corresponding to each wall23. The pair of channels28face each other. A pressing member9is engaged at each channel28. In this embodiment, the continuous surface24does not form only the channel28, but also the groove27to which the fastener is inserted so as to join the end casing3to the main casing2. So the channel28and the groove27can be formed in a single process. As a consequence, productivity is significantly improved.

On a front surface of each pressing member9, a first contacting portion91and a second contacting portion92are formed. The first contacting portion91projects toward the front side along the front end of the first projection26. The second contacting portion92projects toward the front side and contacts at the opposite surface of the front end of the first projection26against the first contacting portion91. The first contacting portion91reaches the front position relative to the second contacting portion92. When each pressing member9is engaged at the channel28corresponding to the pressing member9, a back side surface of the pressing member9contacts the front end of the wall23, a front side surface of the pressing member9contacts the front end of the first projection26, and both the first contacting portion91and the second contacting portion92, which are formed on the front side surface of the pressing member9, contact at the front end of the first projection26. In such the case, the back side surface of each pressing member9contacts the right and left edge portion of the transparent plate5. Thus, the pressing member9presses the transparent plate5toward the back direction.

In this embodiment, pieces of adhesive tape are mounted on the pair of first mounting surfaces22between which the first opening21for passing through the light is disposed. Then, the transparent plate5inserted through space between the pair of first projections26, can be affixed on the adhesive tape7. A distance between the pair of first projections26corresponds to the width of the transparent plate5in the right and left directions. The distance between the pair of first projections26may be set to be slightly wider than the width of the transparent plate5. Therefore, since the transparent5can be inserted from front side toward the back direction of the main casing2, it is easy to affix the transparent plate5on the main casing2via the adhesive tape. Moreover, each pressing member9is engaged at the pair of channels28, and then, the opposite surface of the surface facing the first mounting surface22of the transparent plate5, can be contacted and pressed by the pressing member9. As the result, it can avoid stripping the adhesive tape off. Therefore, the adhesive tape7and the pressing member9can avoid having liquid leak through the first opening21, and can improve tolerance of the photoelectric sensor1.

The adhesive tape and the pressing member9may be mounted on the pair of the first mounting surfaces22between which the first opening21is located. As a result, the transparent plate5can be affixed on the pair of first mounting surface22. Therefore, the adhesive tape7and the pressing member have a linear structure along the first direction, so they can made by cutting to any desirable length from the elongated material instead of preparing various kinds of ring shaped gaskets in the conventional technology As a consequence, productivity is significantly improved.

Moreover, since the first projection26projects toward the front direction and reach the front position relative to the transparent plate5, the transparent plate5can be protected by the first projection26. As a consequence, the strength of the photoelectric sensor1is significantly improved.

FIG. 7shows a cross-sectional view of the photoelectric sensor1according toFIG. 4along the line of B-B. As shown inFIG. 7, on the front surface of the end casing3, a second opening for passing through light between the outside and inside of the end casing3, is formed. The second opening32elongates from one end to the other end of the end casing3. In the emitting device, light irradiated from the emitting element as the optical element4, can be passed through to the outside. In the receiving device, light from the outside can be passed through to the photoelectric device in the end casing3.

On a front surface of the end casing3, a second mounting surface33is formed to a ring shape which surrounds the second opening32. On the second mounting surface33, an adhesive tape is mounted. Then, the transparent plate5is mounted on the adhesive tape. Consequently, the transparent plate5is affixed on the second surface33so that the transparent plate5covers the second opening32.

A pair of second projections is formed of a linear shape on right and left edges on the second mounting surface33along the first direction. The second projections34are disposed paralleled to each other. Distance between the second projections34corresponds to the width of the transparent plate5in the right and left directions. Therefore, when the transparent plate5is affixed on the pair of second mounting surfaces33via the adhesive tape8, the transparent plate5is disposed between the pair of second projections34, and each of the second projections34prevent the shifting of the transparent plate5in the right and left direction.

The pair of second projections34projects toward the front direction and reaches to the same level as the pair of first projections26. When each of the end casings3is joined to the main casing2, the pair of second projections34is disposed continuously with the first projections26corresponding to the second projections34, and is elongated in the same line as each of the first projections26. As a result, in the end casing3, the pair of second projections34which is adjacent to the first projections26and elongated in the same line, can protect the transparent plate5. As a consequence, the strength of the photoelectric sensor1is significantly improved.

A hole35adapted for engaging a pressing member10, is formed on surfaces facing each other, of the pair of second projections34. A hole36adapted for engaging a pressing member10, is formed on the front half of the end surface in the end casing3(referring toFIG. 5). In the pressing member10, three engaging portions101which corresponds to each of the holes35and36, are formed. The pressing member10can be engaged to the end casing3by engaging the engaging portions101to the holes35and36.

In such a case, the pressing member10can be made of bended metal plate, and can include a main plate portion102which contacts the front surface of the transparent plate5; a first side plate portion103and a second side plate portion104which project toward the front direction at both edges of the main plate portion102in the right and left directions; and a third side plate portion105which projects toward the back direction at the end edge of the main plate portion102. The main plate portion102has a first region102A (referring toFIG. 5) for covering the end casing3, and a second region102B for covering the main casing2. In more detail, the first region102A covers the front surface of the end casing3, and the second region102B covers edge portion of the front surface of the main casing2.

Referring toFIG. 5, on the first region102A of the main plate portion102, an aperture106elongating along the first direction, is formed at the center of the first region102A. The first region102A is formed to a ring shape corresponding to the adhesive tape8. Therefore, when the pressing member10is attached to the transparent plate5, the elongated aperture106allows the optical element4in the end casing3to transfer light to be detected between the inside and outside of the end casing3. On the second region102B of the main plate portion102, a hollow portion107is formed. The hollow portion107has a shape which is setback from the center portion of the edge of the main casing2toward the end casing3. Therefore, in the case where the pressing member10is attached on the transparent plate5, the optical element4disposed in the edge portion of the main casing2can transmit the light through the hollow portion107.

Each of the first side plate portions103is formed by bending of both right and left edges of the first region102A in the main plate portion102at the approximately right angles, and projects toward the front side. Two of the three engaging portions101are formed at an edge portion of the main casing2side on the first side plate portion103. In more detail, an incision is formed on each first side portion103so as to form the two engaging portions101. A part of each of the two engaging portions101is separated from the respective first side plate portion103by the incision, and each of the two engaging portions101is bent to the outside. When the pressing member10is attached on the end casing3, a front end portion of the bended part contacts to an internal surface of the hole35corresponding to the bended part.

A front end portion of each of the first side portion103is bent to the outside. In the case where the pressing member10is attached on the end casing3, the bended part contacts an end portion of the first contacting portion91. As a result, the present embodiment can avoid liquid leaking between the first side portion103and the second projection34. Thus, tolerance for preventing the leaking of liquid can be improved.

Each of the second side plate portion104projects toward the front, and inclines for and the outside at both of right edge of the second region102B and left edge of the second region102B in the main plate portion102. When the pressing member10is attached on the end casing3, the outer surface of each second side portion104contacts an edge portion of the pressing member9which is fixed on the main casing2, and presses the edge portion of the pressing member9to the outside. A front end of each of the second side plate portion104is bent to the outside. When the pressing member10is attached to the end casing3, the bended end portion contacts a front end of the first contacting portion91at the end portion of the pressing member9which faces the bended end portion. As a result, the present embodiment can avoid the unfastening of the end portion of the pressing member9from the channel28.

The third side plate portion105projects toward the back side and perpendicularly at the extreme end edge of the main plate portion102. One of the three engaging portions101is formed at the center of the third side plate portion105. The engaging portion101is formed as a bended part at the third side plate portion103by forming an incision. The bended part is a part of the third side plate portion105which is bent to the inside. When the pressing member10is attached on the end casing3, the bended part contacts an inside of the hole36corresponding to the bent part.

In the present embodiment, to both end portions of the main casing2, the end casings3in which the optical element4is installed in the same manner as the main casing2, is joined. Therefore, in the photoelectric sensor1having the main casing2and the end casing3joined at both ends of the main casing2, the optical elements4are arranged from one end to the other end. As a consequence, the photoelectric sensor1is significantly downsized. Moreover, in the end casings3, the leakage of liquid into the second opening32can be avoided by the adhesive tape8and the pressing member10. Thus, the tolerance of the photoelectric sensor1is significantly improved.

Because the end casings3are joined at both ends of the main casing2, the photoelectric sensor1can be formed to any desired length by forming the main casing2to a desired length and joining the end casings3to the main casing2. Thus, it is not necessary to change the length of the end casing3, but the adhesive tape8and the pressing member10can be formed to the same sectional shape. So, productivity can be improved.

In this embodiment, the transparent plate5is affixed to the second mounting surface33of each end casing3via the adhesive tape. Then, the pressing member10is inserted from the front side to each end casing3, and three engaging portions101formed on the pressing member10are engaged at holes35,36corresponding to each engaging portion101. Therefore, the transparent plate5can be fixed by using the pressing member10which presses the opposite surface of mounting surface of the transparent plate5. In other words, it is easy to attach the pressing member10which engages with the engaging portions102only by inserting the pressing member10from the front side onto the end casing3. Therefore, productivity can be improved.

In the present embodiment, the third projection37which projects toward the front side along the extreme end edge of the end casings3is formed on the end casings3. The third projection37extends perpendicular to the extending direction of the second projections34, and reaches to the same level as the height of the second projections34. On the center portion of the third projection37, notch37A is formed from the front end to the back end of the third projection37. When the pressing member10is attached on the end casings3, the pressing member10can contact the backside of the notch37A.

Consequently, in the end casings3, the transparent plate5can be protected by not only the pair of second projections34but also the third projection37. Thus, the strength of the photoelectric sensor1can be improved. In the case where the photoelectric sensor1is used in a situation where the front surface of the photoelectric sensor1faces upwind, the notch37A can drain liquid out from the front surface of the photoelectric sensor1. As the result, the tolerance can be improved.

As shown inFIGS. 6 and 7, an interval between the pair of first projections26and an interval between the pair of second projections34corresponds to the width of the transparent plate5respectively in the right and left direction. Therefore, the transparent plate5which is parallel to the first mounting surface22and second mounting surface33, can be inserted from the outside onto the main casing2and the end casings3through the interval of the pair of first projections26and the pair of second projections34. Then, the transparent plate5can be affixed on the first mounting surface22and the second mounting surface33.

However, the scope of the present invention is not limit to the above mentioned embodiments. For example, an interval between the pair of first projections26and an interval between the pair of second projections34may be wider than the width of the transparent plate5respectively in the right and left directions. In contrast, the intervals may be closet than the width of the transparent plate5. In the case where the interval between the pair of first projections26and the interval between the pair of second projections34are closer than the width of the transparent plate5, the transparent plate5which is inclined to the first mounting surface22and second mounting surface33, can be inserted from front side onto the first mounting surface22and second mounting surface33.

As an embodiment, photoelectric sensors1having a photoelectric element and an emitting element are described. The present invention is applicable to any photoelectric sensor having a photoelectric sensor, and an emitting device for a photoelectric sensor having an emitting element.