SUCTION PAD

A suction pad includes a body and a sponge member. The sponge member made of a material having a semi-open and semi-closed cell structure includes a plurality of cavities opening toward a workpiece, a tubular stopper attached to the body is disposed in each of the cavities of the sponge member, and a suction passage formed in each stopper communicates with a negative pressure chamber formed in the body. The height of the stopper is set to a dimension that prevents the sponge member from being compressed to a maximum compression amount and allows the sponge member to be compressed until the sponge member exhibits airtightness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-197658 filed on Dec. 12, 2022, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a suction pad for sucking a workpiece using vacuum pressure.

Description of the Related Art

Conventionally, there is known a suction pad in which an elastic member made of a material such as rubber is brought into contact with a workpiece and the workpiece is sucked by using vacuum pressure inside the elastic member. Since the elastic member is brought into contact with the workpiece, adhesion to the surface of the workpiece is enhanced, and an impact at the time of contact can be reduced.

JP 2011-073344 A describes an apparatus for taking out a resin molded article by a chuck formed of a base portion having rigidity, and a contact portion having elasticity. The contact portion includes an outer frame contact part in contact with the edge portion of the resin molded article, and an inner contact part divided into a plurality of regions by vacuum grooves. The base portion includes a vacuum suction passage connected to a vacuum pump, and the vacuum suction passage communicates with the vacuum grooves of the contact portion. In this document, as the material of the contact portion, a rubber material is mentioned, and in addition, a material having open cells, closed cells, or semi-closed cells is mentioned.

Since a material having open cells has low airtightness, it is difficult to obtain a necessary vacuum pressure in a case where a member of a suction pad (hereinafter referred to as a “contact member”) in contact with a workpiece is made of a material having only open cells. A material having closed cells has high airtightness, but has high rigidity. Therefore, in a case where the contact member is made of a material having only closed cells, the material is not suitable for sucking a workpiece having irregularities on the surface thereof.

On the other hand, in a case where the contact member is made of a material in which open cells and closed cells are mixed (a material having a semi-open and semi-closed cell structure), flexibility and airtightness necessary for sucking the workpiece can be obtained. When the contact member is compressed, flexibility is exhibited until the volume of the open cells is reduced and the air permeability is lost. Therefore, the contact member is deformed in accordance with the surface shape of the workpiece. Since airtightness is exhibited after the air permeability due to the open cells is lost, vacuum pressure necessary for sucking the workpiece is obtained.

SUMMARY OF THE INVENTION

However, when the workpiece sucking operation and the workpiece releasing operation are repeatedly performed by the contact member made of the material having a semi-open and semi-closed cell structure, the closed cells gradually collapse. As the collapse of the closed cells progresses, the contact member eventually becomes equivalent to a material having only open cells. That is, there is a problem in that the contact member reaches the end of its life in a short period of time.

In addition, when a workpiece having high air permeability such as a corrugated board is sucked by using the contact member made of the material having a semi-open and semi-closed cell structure, the vacuum pressure for sucking the workpiece cannot be sufficiently increased, and the posture of the workpiece becomes unstable. Therefore, there is a possibility that the workpiece largely swings and drops.

The present invention has the object of solving the aforementioned problem.

According to the present invention, there is provided a suction pad, comprising: a body; and a sponge member, wherein the sponge member made of a material having a semi-open and semi-closed cell structure includes a plurality of cavities configured to open toward a workpiece. A stopper having a tubular shape and attached to the body is disposed in each of the cavities of the sponge member, a suction passage formed in the stopper communicates with a negative pressure chamber formed in the body, and a height of the stopper is set to a dimension that prevents the sponge member from being compressed to a maximum compression amount and allows the sponge member to be compressed until the sponge member exhibits airtightness.

In the suction pad according to the present invention, since the stopper for preventing the sponge member from being compressed to the maximum compression amount is disposed in each cavity of the sponge member, the life of the sponge member made of a material having a semi-open and semi-closed cell structure is improved. In addition, when the workpiece having high air permeability is sucked and conveyed, even if acceleration acts on the workpiece, the workpiece abuts against the stopper, thereby suppressing the swing of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

A suction pad10according to a first embodiment of the present invention will be described with reference toFIGS.1to6. As shown inFIGS.1and2, the suction pad10includes a body12, a sponge member20, and a plurality of stoppers26. In the following description, when terms in relation to upper and lower directions are used, such terms refer to the directions shown in the drawings, however, the actual arrangement of the respective constituent members is not limited thereby.

The body12is formed of a main body12athat has a box shape and opens downward, and a plate12bthat covers the main body12afrom below. The main body12aincludes a suction port14connected to a vacuum generating device (not shown). The body12includes therein a negative pressure chamber16communicating with the suction port14. The plate12bincludes a plurality of holes18communicating with the negative pressure chamber16. InFIG.2, the suction port14is shown to be located on the lateral side of the body12for the sake of convenience.

The sponge member20having a plate shape is attached to a lower surface of the plate12bby means of bonding or the like. The sponge member20is made of a material having a semi-open and semi-closed cell structure, and is manufactured by foam-molding ethylene propylene rubber (EPDM), for example. The sponge member20includes a plurality of cavities22opening toward a workpiece. The cavities22of the sponge member20are formed at positions corresponding to the holes18of the body12. The sponge member20comes into contact with the workpiece at a lower surface24thereof.

The thickness of the sponge member20when no vertical compressive force is applied to the sponge member20is represented by TO, and the thickness of the sponge member20when a vertical compressive force is applied to the sponge member20is represented by T. Then, a compression amount (%) of the sponge member20is defined as (T0−T)/T0×100. Although depending on the ratio of open cells and closed cells, the sponge member20exhibits sufficient airtightness when compressed to a compression amount of at least about 70%, for example.

Further, although depending on the ratio of the open cells and the closed cells, when the sponge member20is compressed to a compression amount of about 90%, for example, the flexibility due to the open cells is lost and the rigidity is rapidly increased. The compression amount at which the sponge member20loses flexibility is hereinafter referred to as a “maximum compression amount”. When the sponge member20is repeatedly compressed to the maximum compression amount and released, the collapse of the closed cells progresses, and eventually the sponge member20ceases to exhibit airtightness.

Each of the stoppers26having a tubular shape is attached to the lower surface of the plate12band is disposed in the cavity22of the sponge member20. The stopper26has a certain degree of elasticity so as to weaken an impact when colliding with the workpiece, and is made of, for example, a rubber material. The stoppers26each include a suction passage28penetrating the stopper26in the height direction (vertical direction) thereof, and the suction passage28communicates with the negative pressure chamber16via the hole18of the body12.

The stopper26acts to limit the compression amount of the sponge member20so that the sponge member20is not compressed to the maximum compression amount. A height (axial length) H of the stopper26is set to a dimension that prevents the sponge member20from being compressed to the maximum compression amount. In addition, the height H of the stopper26is set to a dimension that allows the sponge member20to be compressed until the sponge member20exhibits high airtightness.

In a state where no compressive force acts on the sponge member20, the height H of the stopper26is preferably set to be about 13% to 35% of a length L of the cavity22of the sponge member20, for example. If the height H of the stopper26is too small with respect to the length L of the cavity22of the sponge member20, the compression amount of the sponge member20becomes excessively large, and there is a possibility that the collapse of the closed cells progresses to shorten the life of the sponge member20. If the height H of the stopper26is too large with respect to the length L of the cavity22of the sponge member20, there is a possibility that sufficient airtightness cannot be obtained.

The workpiece can be steadily (stably) held by the suction pad10in a state of being in abutment against the stoppers26or in a state of not being in abutment against the stoppers26. Whether the workpiece is held by the suction pad10in a state of being in abutment against the stoppers26or the workpiece is held by the suction pad10in a state of not being in abutment against the stoppers26greatly depends on the air permeability of the workpiece and a weight of the workpiece. Hereinafter, the force acting on the workpiece when the workpiece is steadily held by the suction pad10will be considered.

A total negative pressure ΔP generated in the suction passages28(a difference between the atmospheric pressure and the pressure in the suction passages28) depends on the air permeability of the workpiece. The negative pressure ΔP generated in the suction passages28increases as the air permeability of the workpiece decreases. The workpiece is lifted upward by the negative pressure ΔP generated in the suction passages28. In a state where the workpiece is in abutment against the stoppers26, the force for lifting the workpiece upward (hereinafter referred to as a “lifting force”) is represented by ΔP·S1, where S1 represents a total opening area of the suction passages28of the stoppers26.

In a state where the workpiece is not in abutment against the stoppers26, the lifting force is represented by ΔP·S2, where S2 represents a total opening area of the cavities22of the sponge member20. Since the opening area S2 of the cavities22of the sponge member20is larger than the opening area $1 of the suction passages28of the stoppers26, the lifting force in a state where the workpiece is not in abutment against the stoppers26is larger than the lifting force in a state where the workpiece is in abutment against the stoppers26. An upward force acting on the workpiece is only the lifting force.

A downward force acting on the workpiece includes, in addition to the weight of the workpiece and a repulsive force caused by the compression of the sponge member20, a repulsive force caused by the deformation of the stoppers26when the workpiece is in abutment against the stoppers26. In a state where the workpiece is in abutment against the stoppers26, the downward force acting on the workpiece is represented by (w+F1+F2), where w represents the weight of the workpiece, F1 represents a repulsive force of the sponge member20, and F2 represents a total repulsive force of the stoppers26.

In a state where the workpiece is not in abutment against the stoppers26, the downward force acting on the workpiece is represented by (w+F1′), where w represents the weight of the workpiece and F1′ is a repulsive force of the sponge member20. Since the amount by which the sponge member20is compressed in a state where the workpiece is not in abutment against the stoppers26is smaller than the amount by which the sponge member20is compressed in a state where the workpiece is in abutment against the stoppers26, F1′ is smaller than F1.

In a case where the workpiece is stably held in a state of being in abutment against the stoppers26, ΔP·S1=w+F1+F2 (Formula 1) is established. In a case where the workpiece is stably held in a state of not being in abutment against the stoppers26, ΔP·S2=w+F1′ (Formula 2) is established. As described above, ΔP depends on the air permeability of the workpiece, S2 is larger than S1, and F1′ is smaller than F1. F1 and F1′ change according to the compression amount of the sponge member20, and F2 changes according to the deformation amount of the stoppers26.

In a case where the air permeability of the workpiece is low and the negative pressure ΔP generated in the suction passages28of the stoppers26is high, if the weight w of the workpiece is not excessively large, Formula 1 is established and the workpiece is stably held in a state of being in abutment against the stoppers26. In a case where the air permeability of the workpiece is high and the negative pressure ΔP generated in the suction passages28of the stoppers26is low, if the weight w of the workpiece is not excessively large, Formula 2 is established and the workpiece is stably held in a state of not being in abutment against the stoppers26.

Since the lifting force rapidly changes before and after the workpiece is displaced upward and abuts against the stoppers26, the workpiece may not be stably held. That is, the following phenomenon is repeated: when the workpiece is lifted and abuts against the stoppers26, the lifting force is suddenly reduced and the workpiece is separated from the stoppers26, and when the workpiece is separated from the stoppers26, the lifting force is suddenly increased and the workpiece is lifted and abuts against the stoppers26. This phenomenon can be described as a state where the workpiece is held at a position separated from the stoppers26by a minute gap.

FIG.3shows a state where a workpiece W1having low air permeability is sucked and held by the suction pad10. Since the negative pressure ΔP generated in the suction passages28of the stoppers26is high and the lifting force is large, the workpiece W1is stably held in a state of being abutment against the stoppers26. In the present embodiment, the compression amount of the sponge member20is 70% or more. The sponge member20is compressed to such an extent that sufficient airtightness can be exhibited. Further, since the sponge member20is not compressed to the maximum compression amount, the life of the sponge member20is improved.

FIG.4shows a state where a workpiece W2having high air permeability such as a corrugated board is sucked and held by the suction pad10. Since the negative pressure ΔP generated in the suction passages28of the stoppers26is low and the lifting force is small, the upward force and the downward force acting on the workpiece W2are balanced in a state where the compression amount of the sponge member20is small. Therefore, the workpiece W2is held in a state of not being in abutment against the stoppers26.

As described above, when conveying the workpiece W2that is sucked and held in a state where the compression amount of the sponge member20is small, if acceleration acts on the workpiece W2, the workpiece W2tries to swing. However, as shown by a two dot chain line inFIG.4, the inclination of the workpiece W2is suppressed to be small by abutment of the workpiece W2against the stopper26. Therefore, the swing of the workpiece W2is suppressed, and the workpiece W2is prevented from dropping.

Since the sponge member20exhibits flexibility even when the compression amount thereof is small, the sponge member20is deformed in accordance with the surface shape of the workpiece W2even if the workpiece W2has irregularities on its surface as in the case of a cardboard box in which beverage containers are packaged. Therefore, no gap is formed between the lower surface24of the sponge member20and the workpiece W2, and the airtightness is prevented from being lowered.

Incidentally, when the sponge member20is compressed, there is a possibility that an outer peripheral portion thereof that is in contact with the atmosphere is deformed so as to be inclined inward. When the outer peripheral portion of the sponge member20is largely inclined inward, a gap is formed between the lower surface24of the sponge member20and the surface of the workpiece at that inclined portion, and one or some of the plurality of cavities22communicate with the atmosphere, thereby reducing airtightness. The stoppers26also function to suppress the inclination of the outer peripheral portion of the sponge member20.

FIG.6shows a state where the outer peripheral portion of the sponge member20is largely inclined when the stoppers26are not present. Depending on the location, there is a gap between the outer peripheral portion of the sponge member20and the workpiece W. On the other hand, when the stoppers26are present, inward inclination of the outer peripheral portion of the sponge member20is suppressed as shown inFIG.5. The effect of suppressing the inclination of the outer peripheral portion of the sponge member20increases as the difference between the outer diameter of each stopper26and the inner diameter of each cavity22of the sponge member20decreases.

When the sponge member20is compressed, the inner diameter of the cavity22is reduced. In order not to affect the compression of the sponge member20, it is necessary that the inner diameter of the cavity22when no compressive force acts on the sponge member20is set to be larger than the outer diameter of the stopper26. Accordingly, the outer diameter of the stopper26is preferably about 80% to 90% of the inner diameter of the cavity22, for example. The outer diameter of the stopper26disposed on the outer peripheral portion of the sponge member20may be larger than the outer diameter of the other stoppers26.

In the suction pad10according to the present embodiment, the stoppers26that prevent the sponge member20from being compressed to the maximum compression amount are disposed in the cavities22of the sponge member20. Therefore, the life of the sponge member20made of a material having a semi-open and semi-closed cell structure is improved. Further, when the workpiece having high air permeability is sucked and conveyed, even if acceleration acts on the workpiece, the workpiece abuts against the stopper26, thereby suppressing the swing of the workpiece.

Second Embodiment

Next, a suction pad30according to a second embodiment of the present invention will be described with reference toFIGS.7and8. In the suction pad30according to the second embodiment, constituent elements that are the same as or equivalent to those of the above-described suction pad10are denoted by the same reference numerals, and detailed description thereof is omitted.

The suction pad30is useful for sucking workpieces of various sizes including a workpiece having such a size that it covers only one or some of the plurality of cavities22of the sponge member20. A flow passage adjustment valve34for adjusting a flow passage area in accordance with a suction state of the workpiece is arranged in a flow passage that connects each cavity22and the negative pressure chamber16. The flow passage adjustment valve34is incorporated in each stopper32. Hereinafter, the stopper32and the flow passage adjustment valve34will be described in detail.

The stoppers32are each made of a rubber material and formed in a tubular shape. A lower portion of each stopper32includes an annular first flange portion32aon its outer periphery, and an annular groove portion32bon its inner periphery. An upper portion of each stopper32includes an annular bulging portion32con its outer periphery, and a second flange portion32don its inner periphery. The stoppers32are respectively inserted into engagement holes19provided in the plate12bof the body12, and a portion of the plate12baround each engagement hole19is held between the first flange portion32aand the bulging portion32c. As a result, the stoppers32are fixed to the plate12b, and the lower portions of the stoppers32protrude downward from the plate12b. The second flange portion32dof each stopper32forms an air passage on the inner peripheral side thereof.

The flow passage adjustment valves34each include a tubular valve housing36and a tubular valve element38. A lower portion of the valve housing36includes an annular flange portion36aon its outer periphery. The flange portion36aengages with the groove portion32bof the stopper32, whereby the valve housing36is fixed to the inside of the stopper32. The valve element38is disposed inside the valve housing36and can be vertically displaced with respect to the valve housing36. The valve housing36includes a tapered seat portion36bagainst which a head part of the valve element38can abut. A spring40for biasing the valve element38downward is disposed between the valve housing36and the valve element38. A regulating member42capable of abutting against a lower end of the valve element38is attached to the valve housing36, and by the valve element38abutting against the regulating member42, downward displacement of the valve element38is regulated. The regulating member42is formed in a mesh shape and has air permeability.

The head part of the valve element38includes an orifice38aat its center, and a sidewall of the valve element38includes a plurality of openings38b. The area of the opening38bis sufficiently larger than the area of the orifice38a. In a state where the head part of the valve element38is separated from the seat portion36bof the valve housing36, each cavity22of the sponge member20communicates with the negative pressure chamber16via the orifice38aand the plurality of openings38bof the valve element38. In a state where the head part of the valve element38is in abutment against the seat portion36bof the valve housing36, each cavity22of the sponge member20communicates with the negative pressure chamber16only via the orifice38aof the valve element38.

When the cavity22of the sponge member20is closed by the workpiece, the flow passage area in the flow passage adjustment valve34is sufficiently increased, and the pressure in the cavity22becomes equal to the pressure in the negative pressure chamber16. When the cavity22is not closed by the workpiece, the flow passage area in the flow passage adjustment valve34is sufficiently decreased, and high vacuum pressure is generated in the negative pressure chamber16, while the pressure in the cavity22becomes substantially equal to the atmospheric pressure. This will be described in more detail below.

When vacuum pressure is generated in the negative pressure chamber16in a state where the cavity22is not closed by the workpiece, air passes through the orifice38aof the valve element38from the lower side toward the upper side at a high flow velocity. Therefore, the valve element38is displaced upward by the pressure difference generated before and after the orifice38a, and the head part of the valve element38abuts against the seat portion36bof the valve housing36. When the head part of the valve element38abuts against the seat portion36b, the flow passage area decreases, and the flow velocity of the air passing through the orifice38afurther increases. As a result, the state where the head part of the valve element38is in abutment against the seat portion36bof the valve housing36is reliably maintained.

When the cavity22is closed by the workpiece, the flow rate of the air passing through the orifice38aof the valve element38decreases, and the flow velocity of the air passing through the orifice38adecreases. Therefore, the pressure difference generated before and after the orifice38abecomes small, the valve element38is displaced downward by the biasing force of the spring40, and the head part of the valve element38moves away from the seat portion36bof the valve housing36. When the head part of the valve element38moves away from the seat portion36b, the flow passage area increases.

The suction pad30can suck workpieces of various sizes. The pressure in the negative pressure chamber16of the body12does not increase even if the workpiece is small enough to contact only a part of the lower surface24of the sponge member20and one or some of the cavities22of the sponge member20are open to the atmosphere. That is, even if there is a cavity22which is not closed by the workpiece, the vacuum pressure generated in the negative pressure chamber16does not decrease due to the action of the flow passage adjustment valve34.

In the suction pad30according to the present embodiment, since the stoppers32are disposed in the cavities22of the sponge member20, the life of the sponge member20is improved, and the swing of the workpiece is suppressed even if acceleration acts on the workpiece. Further, since the flow passage adjustment valve34for adjusting the flow passage area in accordance with the suction state of the workpiece is incorporated in each stopper32, the flow passage adjustment valve34can be easily and compactly disposed.

Although the valve element38according to the present embodiment includes the orifice38ain the head part thereof, the valve element38may not include the orifice38ain the head part thereof. In this case, when the head part of the valve element38abuts against the seat portion36bof the valve housing36, the cavity22of the sponge member20is shut off from the negative pressure chamber16. Therefore, the amount of air flowing from the cavity22that is not closed by the workpiece toward the negative pressure chamber16becomes 0, and extremely high vacuum pressure is obtained in the negative pressure chamber16and the cavity22that is closed by the workpiece.

The present invention is not limited to the above disclosure, and various modifications are possible without departing from the essence and gist of the present invention.