Patent Description:
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.

<CIT> 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.

As the art related to the present invention, <CIT>, <CIT>, and <CIT> can be listed.

<CIT> discloses a soft grip head including a suction pad with a plurality of suction cells, and flexible supporting part formed of a coil spring disposed in the space inside of each of the suction cells. The suction pad is divided by flexible sidewalls, to form the plurality of the suction cells. An inlet formed at the lower end of the suction pad makes contact with a workpiece. The shape of a part of the inlet is freely changed to follow the shape of the surface of the workpiece when tightly attached to the workpiece.

<CIT> discloses a suction gripper head reduced its weight by using a foam body. A soleplate for coming directly into contact with a workpiece is secured to the body. The soleplate is also made of foam with a plurality of cells. The foam of the body could be based on or made of a material that has a cellular structure with cells that may be closed, semi-open, open.

<CIT> discloses a resin molding takeoff device having a chuck, a vacuum pump, a heater and an arm. A contact portion of the chuck is preferably made of heat-resistant urethane, silicone rubber, fluorine rubber, and preferably made of a material having interconnected cells, closed cells or semi-closed cells.

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.

This problem is solved by the suction pad according to claim <NUM>. Preferred embodiments of the invention are evident from the dependent claims.

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.

A suction pad <NUM> according to a first embodiment of the present invention will be described with reference to <FIG>. As shown in <FIG> and <FIG>, the suction pad <NUM> includes a body <NUM>, a sponge member <NUM>, and a plurality of stoppers <NUM>. 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 body <NUM> is formed of a main body 12a that has a box shape and opens downward, and a plate 12b that covers the main body 12a from below. The main body 12a includes a suction port <NUM> connected to a vacuum generating device (not shown). The body <NUM> includes therein a negative pressure chamber <NUM> communicating with the suction port <NUM>. The plate 12b includes a plurality of holes <NUM> communicating with the negative pressure chamber <NUM>. In <FIG>, the suction port <NUM> is shown to be located on the lateral side of the body <NUM> for the sake of convenience.

The sponge member <NUM> having a plate shape is attached to a lower surface of the plate 12b by means of bonding or the like. The sponge member <NUM> is 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 member <NUM> includes a plurality of cavities <NUM> opening toward a workpiece. The cavities <NUM> of the sponge member <NUM> are formed at positions corresponding to the holes <NUM> of the body <NUM>. The sponge member <NUM> comes into contact with the workpiece at a lower surface <NUM> thereof.

The thickness of the sponge member <NUM> when no vertical compressive force is applied to the sponge member <NUM> is represented by T0, and the thickness of the sponge member <NUM> when a vertical compressive force is applied to the sponge member <NUM> is represented by T. Then, a compression amount (%) of the sponge member <NUM> is defined as (T0 - T)/T0 × <NUM>. Although depending on the ratio of open cells and closed cells, the sponge member <NUM> exhibits sufficient airtightness when compressed to a compression amount of at least about <NUM> %, for example.

Further, although depending on the ratio of the open cells and the closed cells, when the sponge member <NUM> is compressed to a compression amount of about <NUM> %, for example, the flexibility due to the open cells is lost and the rigidity is rapidly increased. The compression amount at which the sponge member <NUM> loses flexibility is hereinafter referred to as a "maximum compression amount". When the sponge member <NUM> is repeatedly compressed to the maximum compression amount and released, the collapse of the closed cells progresses, and eventually the sponge member <NUM> ceases to exhibit airtightness.

Each of the stoppers <NUM> having a tubular shape is attached to the lower surface of the plate 12b and is disposed in the cavity <NUM> of the sponge member <NUM>. The stopper <NUM> has 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 stoppers <NUM> each include a suction passage <NUM> penetrating the stopper <NUM> in the height direction (vertical direction) thereof, and the suction passage <NUM> communicates with the negative pressure chamber <NUM> via the hole <NUM> of the body <NUM>.

The stopper <NUM> acts to limit the compression amount of the sponge member <NUM> so that the sponge member <NUM> is not compressed to the maximum compression amount. A height (axial length) H of the stopper <NUM> is set to a dimension that prevents the sponge member <NUM> from being compressed to the maximum compression amount. In addition, the height H of the stopper <NUM> is set to a dimension that allows the sponge member <NUM> to be compressed until the sponge member <NUM> exhibits high airtightness.

In a state where no compressive force acts on the sponge member <NUM>, the height H of the stopper <NUM> is preferably set to be about <NUM> % to <NUM> % of a length L of the cavity <NUM> of the sponge member <NUM>, for example. If the height H of the stopper <NUM> is too small with respect to the length L of the cavity <NUM> of the sponge member <NUM>, the compression amount of the sponge member <NUM> becomes excessively large, and there is a possibility that the collapse of the closed cells progresses to shorten the life of the sponge member <NUM>. If the height H of the stopper <NUM> is too large with respect to the length L of the cavity <NUM> of the sponge member <NUM>, there is a possibility that sufficient airtightness cannot be obtained.

The workpiece can be steadily (stably) held by the suction pad <NUM> in a state of being in abutment against the stoppers <NUM> or in a state of not being in abutment against the stoppers <NUM>. Whether the workpiece is held by the suction pad <NUM> in a state of being in abutment against the stoppers <NUM> or the workpiece is held by the suction pad <NUM> in a state of not being in abutment against the stoppers <NUM> greatly 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 pad <NUM> will be considered.

A total negative pressure ΔP generated in the suction passages <NUM> (a difference between the atmospheric pressure and the pressure in the suction passages <NUM>) depends on the air permeability of the workpiece. The negative pressure ΔP generated in the suction passages <NUM> increases as the air permeability of the workpiece decreases. The workpiece is lifted upward by the negative pressure ΔP generated in the suction passages <NUM>. In a state where the workpiece is in abutment against the stoppers <NUM>, 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 passages <NUM> of the stoppers <NUM>.

In a state where the workpiece is not in abutment against the stoppers <NUM>, the lifting force is represented by ΔP·S2, where S2 represents a total opening area of the cavities <NUM> of the sponge member <NUM>. Since the opening area S2 of the cavities <NUM> of the sponge member <NUM> is larger than the opening area S1 of the suction passages <NUM> of the stoppers <NUM>, the lifting force in a state where the workpiece is not in abutment against the stoppers <NUM> is larger than the lifting force in a state where the workpiece is in abutment against the stoppers <NUM>. 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 member <NUM>, a repulsive force caused by the deformation of the stoppers <NUM> when the workpiece is in abutment against the stoppers <NUM>. In a state where the workpiece is in abutment against the stoppers <NUM>, 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 member <NUM>, and F2 represents a total repulsive force of the stoppers <NUM>.

In a state where the workpiece is not in abutment against the stoppers <NUM>, 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 member <NUM>. Since the amount by which the sponge member <NUM> is compressed in a state where the workpiece is not in abutment against the stoppers <NUM> is smaller than the amount by which the sponge member <NUM> is compressed in a state where the workpiece is in abutment against the stoppers <NUM>, F1' is smaller than F1.

In a case where the workpiece is stably held in a state of being in abutment against the stoppers <NUM>, ΔP·S1 = w + F1 + F2 (Formula <NUM>) is established. In a case where the workpiece is stably held in a state of not being in abutment against the stoppers <NUM>, ΔP·S2 = w + F1' (Formula <NUM>) 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 member <NUM>, and F2 changes according to the deformation amount of the stoppers <NUM>.

In a case where the air permeability of the workpiece is low and the negative pressure ΔP generated in the suction passages <NUM> of the stoppers <NUM> is high, if the weight w of the workpiece is not excessively large, Formula <NUM> is established and the workpiece is stably held in a state of being in abutment against the stoppers <NUM>. In a case where the air permeability of the workpiece is high and the negative pressure ΔP generated in the suction passages <NUM> of the stoppers <NUM> is low, if the weight w of the workpiece is not excessively large, Formula <NUM> is established and the workpiece is stably held in a state of not being in abutment against the stoppers <NUM>.

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

<FIG> shows a state where a workpiece W1 having low air permeability is sucked and held by the suction pad <NUM>. Since the negative pressure ΔP generated in the suction passages <NUM> of the stoppers <NUM> is high and the lifting force is large, the workpiece W1 is stably held in a state of being abutment against the stoppers <NUM>. In the present embodiment, the compression amount of the sponge member <NUM> is <NUM> % or more. The sponge member <NUM> is compressed to such an extent that sufficient airtightness can be exhibited. Further, since the sponge member <NUM> is not compressed to the maximum compression amount, the life of the sponge member <NUM> is improved.

<FIG> shows a state where a workpiece W2 having high air permeability such as a corrugated board is sucked and held by the suction pad <NUM>. Since the negative pressure ΔP generated in the suction passages <NUM> of the stoppers <NUM> is low and the lifting force is small, the upward force and the downward force acting on the workpiece W2 are balanced in a state where the compression amount of the sponge member <NUM> is small. Therefore, the workpiece W2 is held in a state of not being in abutment against the stoppers <NUM>.

As described above, when conveying the workpiece W2 that is sucked and held in a state where the compression amount of the sponge member <NUM> is small, if acceleration acts on the workpiece W2, the workpiece W2 tries to swing. However, as shown by a two dot chain line in <FIG>, the inclination of the workpiece W2 is suppressed to be small by abutment of the workpiece W2 against the stopper <NUM>. Therefore, the swing of the workpiece W2 is suppressed, and the workpiece W2 is prevented from dropping.

Since the sponge member <NUM> exhibits flexibility even when the compression amount thereof is small, the sponge member <NUM> is deformed in accordance with the surface shape of the workpiece W2 even if the workpiece W2 has 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 surface <NUM> of the sponge member <NUM> and the workpiece W2, and the airtightness is prevented from being lowered.

Incidentally, when the sponge member <NUM> is 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 member <NUM> is largely inclined inward, a gap is formed between the lower surface <NUM> of the sponge member <NUM> and the surface of the workpiece at that inclined portion, and one or some of the plurality of cavities <NUM> communicate with the atmosphere, thereby reducing airtightness. The stoppers <NUM> also function to suppress the inclination of the outer peripheral portion of the sponge member <NUM>.

<FIG> shows a state where the outer peripheral portion of the sponge member <NUM> is largely inclined when the stoppers <NUM> are not present. Depending on the location, there is a gap between the outer peripheral portion of the sponge member <NUM> and the workpiece W. On the other hand, when the stoppers <NUM> are present, inward inclination of the outer peripheral portion of the sponge member <NUM> is suppressed as shown in <FIG>. The effect of suppressing the inclination of the outer peripheral portion of the sponge member <NUM> increases as the difference between the outer diameter of each stopper <NUM> and the inner diameter of each cavity <NUM> of the sponge member <NUM> decreases.

When the sponge member <NUM> is compressed, the inner diameter of the cavity <NUM> is reduced. In order not to affect the compression of the sponge member <NUM>, it is necessary that the inner diameter of the cavity <NUM> when no compressive force acts on the sponge member <NUM> is set to be larger than the outer diameter of the stopper <NUM>. Accordingly, the outer diameter of the stopper <NUM> is preferably about <NUM> % to <NUM> % of the inner diameter of the cavity <NUM>, for example. The outer diameter of the stopper <NUM> disposed on the outer peripheral portion of the sponge member <NUM> may be larger than the outer diameter of the other stoppers <NUM>.

In the suction pad <NUM> according to the present embodiment, the stoppers <NUM> that prevent the sponge member <NUM> from being compressed to the maximum compression amount are disposed in the cavities <NUM> of the sponge member <NUM>. Therefore, the life of the sponge member <NUM> made 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 stopper <NUM>, thereby suppressing the swing of the workpiece.

Next, a suction pad <NUM> according to a second embodiment of the present invention will be described with reference to <FIG> and <FIG>. In the suction pad <NUM> according to the second embodiment, constituent elements that are the same as or equivalent to those of the above-described suction pad <NUM> are denoted by the same reference numerals, and detailed description thereof is omitted.

The suction pad <NUM> is 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 cavities <NUM> of the sponge member <NUM>. A flow passage adjustment valve <NUM> for adjusting a flow passage area in accordance with a suction state of the workpiece is arranged in a flow passage that connects each cavity <NUM> and the negative pressure chamber <NUM>. The flow passage adjustment valve <NUM> is incorporated in each stopper <NUM>. Hereinafter, the stopper <NUM> and the flow passage adjustment valve <NUM> will be described in detail.

The stoppers <NUM> are each made of a rubber material and formed in a tubular shape. A lower portion of each stopper <NUM> includes an annular first flange portion 32a on its outer periphery, and an annular groove portion 32b on its inner periphery. An upper portion of each stopper <NUM> includes an annular bulging portion 32c on its outer periphery, and a second flange portion 32d on its inner periphery. The stoppers <NUM> are respectively inserted into engagement holes <NUM> provided in the plate 12b of the body <NUM>, and a portion of the plate 12b around each engagement hole <NUM> is held between the first flange portion 32a and the bulging portion 32c. As a result, the stoppers <NUM> are fixed to the plate 12b, and the lower portions of the stoppers <NUM> protrude downward from the plate 12b. The second flange portion 32d of each stopper <NUM> forms an air passage on the inner peripheral side thereof.

The flow passage adjustment valves <NUM> each include a tubular valve housing <NUM> and a tubular valve element <NUM>. A lower portion of the valve housing <NUM> includes an annular flange portion 36a on its outer periphery. The flange portion 36a engages with the groove portion 32b of the stopper <NUM>, whereby the valve housing <NUM> is fixed to the inside of the stopper <NUM>. The valve element <NUM> is disposed inside the valve housing <NUM> and can be vertically displaced with respect to the valve housing <NUM>. The valve housing <NUM> includes a tapered seat portion 36b against which a head part of the valve element <NUM> can abut. A spring <NUM> for biasing the valve element <NUM> downward is disposed between the valve housing <NUM> and the valve element <NUM>. A regulating member <NUM> capable of abutting against a lower end of the valve element <NUM> is attached to the valve housing <NUM>, and by the valve element <NUM> abutting against the regulating member <NUM>, downward displacement of the valve element <NUM> is regulated. The regulating member <NUM> is formed in a mesh shape and has air permeability.

The head part of the valve element <NUM> includes an orifice 38a at its center, and a sidewall of the valve element <NUM> includes a plurality of openings 38b. The area of the opening 38b is sufficiently larger than the area of the orifice 38a. In a state where the head part of the valve element <NUM> is separated from the seat portion 36b of the valve housing <NUM>, each cavity <NUM> of the sponge member <NUM> communicates with the negative pressure chamber <NUM> via the orifice 38a and the plurality of openings 38b of the valve element <NUM>. In a state where the head part of the valve element <NUM> is in abutment against the seat portion 36b of the valve housing <NUM>, each cavity <NUM> of the sponge member <NUM> communicates with the negative pressure chamber <NUM> only via the orifice 38a of the valve element <NUM>.

When the cavity <NUM> of the sponge member <NUM> is closed by the workpiece, the flow passage area in the flow passage adjustment valve <NUM> is sufficiently increased, and the pressure in the cavity <NUM> becomes equal to the pressure in the negative pressure chamber <NUM>. When the cavity <NUM> is not closed by the workpiece, the flow passage area in the flow passage adjustment valve <NUM> is sufficiently decreased, and high vacuum pressure is generated in the negative pressure chamber <NUM>, while the pressure in the cavity <NUM> becomes substantially equal to the atmospheric pressure. This will be described in more detail below.

When vacuum pressure is generated in the negative pressure chamber <NUM> in a state where the cavity <NUM> is not closed by the workpiece, air passes through the orifice 38a of the valve element <NUM> from the lower side toward the upper side at a high flow velocity. Therefore, the valve element <NUM> is displaced upward by the pressure difference generated before and after the orifice 38a, and the head part of the valve element <NUM> abuts against the seat portion 36b of the valve housing <NUM>. When the head part of the valve element <NUM> abuts against the seat portion 36b, the flow passage area decreases, and the flow velocity of the air passing through the orifice 38a further increases. As a result, the state where the head part of the valve element <NUM> is in abutment against the seat portion 36b of the valve housing <NUM> is reliably maintained.

When the cavity <NUM> is closed by the workpiece, the flow rate of the air passing through the orifice 38a of the valve element <NUM> decreases, and the flow velocity of the air passing through the orifice 38a decreases. Therefore, the pressure difference generated before and after the orifice 38a becomes small, the valve element <NUM> is displaced downward by the biasing force of the spring <NUM>, and the head part of the valve element <NUM> moves away from the seat portion 36b of the valve housing <NUM>. When the head part of the valve element <NUM> moves away from the seat portion 36b, the flow passage area increases.

The suction pad <NUM> can suck workpieces of various sizes. The pressure in the negative pressure chamber <NUM> of the body <NUM> does not increase even if the workpiece is small enough to contact only a part of the lower surface <NUM> of the sponge member <NUM> and one or some of the cavities <NUM> of the sponge member <NUM> are open to the atmosphere. That is, even if there is a cavity <NUM> which is not closed by the workpiece, the vacuum pressure generated in the negative pressure chamber <NUM> does not decrease due to the action of the flow passage adjustment valve <NUM>.

In the suction pad <NUM> according to the present embodiment, since the stoppers <NUM> are disposed in the cavities <NUM> of the sponge member <NUM>, the life of the sponge member <NUM> is improved, and the swing of the workpiece is suppressed even if acceleration acts on the workpiece. Further, since the flow passage adjustment valve <NUM> for adjusting the flow passage area in accordance with the suction state of the workpiece is incorporated in each stopper <NUM>, the flow passage adjustment valve <NUM> can be easily and compactly disposed.

Claim 1:
A suction pad (<NUM>) comprising: a body (<NUM>); and a sponge member (<NUM>),
wherein the sponge member (<NUM>) includes a plurality of cavities (<NUM>) configured to open toward a workpiece,
a stopper (<NUM>) attached to the body (<NUM>) is disposed in each of the cavities (<NUM>) of the sponge member (<NUM>), a suction passage (<NUM>) formed in the stopper (<NUM>) communicates with a negative pressure chamber (<NUM>) formed in the body (<NUM>), characterized in that
the sponge member (<NUM>) is made of a material having a semi-open and semi-closed cell structure,
the stopper (<NUM>) has a tubular shape, and
a height of the stopper (<NUM>) is set to a dimension that prevents the sponge member (<NUM>) from being compressed to a maximum compression amount and allows the sponge member (<NUM>) to be compressed until the sponge member (<NUM>) exhibits airtightness.