Patent Description:
Conventionally, there is known a suction pad that sucks a workpiece by bringing a sponge member made of a porous material into contact with the workpiece and generating vacuum pressure inside the sponge member. There is also known a technique for detecting the suction state of a workpiece by detecting pressure in a path through which vacuum pressure is introduced into a suction pad.

For example, <CIT> discloses a suction pad including an inner sponge pad formed of an open cell sponge having air permeability, and an outer sponge pad formed of a closed cell sponge having no air permeability. A pressure sensor is disposed on a path through which the suction pad is connected to an ejector, and the suction state of the workpiece sucked by the inner sponge pad and the suction state of the workpiece sucked by the outer sponge pad are sequentially detected. As the art related to the present invention, <CIT>, <CIT> and <CIT> can be listed.

<CIT> discloses a gripper assembly including a vacuum generation head, a plenum block, a check valve plate, and a gripper having foam structure. The check valve plate is formed of a number of chambers, and each of the chambers includes an opening facing the bottom, a ball blocking a vacuum supply conduit, an opening connected to the plenum block, and a pressure sensor. Each of the openings and each of the chambers individually correspond to a plurality of holes (ports) of the gripper. The vacuum supply conduit corresponding to the port in contact with the workpiece is not to be blocked by the ball and the corresponding pressure sensor indicates vacuum pressure. The vacuum supply conduit corresponding to the port out of contact with the workpiece is to be blocked by the ball and the pressure sensor indicates atmospheric pressure.

<CIT> discloses a suction device having a body including a cavity and an open end of the cavity functioning as a suction face to suck a workpiece. A tangential nozzle is disposed on a sidewall surface of the cavity. A suction hole is disposed on the closed end face of the cavity. The suction hole is connected to a suction unit. <CIT> discloses a suction device provided with a pressure detection unit to monitor the fluid pressure in the cavity.

<CIT> discloses a vacuum suction device capable of estimating a suction area and a suction force. This vacuum suction device includes a vacuum suction pad, an air injection means, a depressurization means, a positive pressure measurement means, a negative pressure measurement means, a conduit for pressurization and a conduit for depressurization. The vacuum suction pad includes a vacuum chamber forming unit internally forming a vacuum chamber, a suction unit having a workpiece suction face and a check valve forming unit. The suction unit is formed of a sponge material or the like and provided with a plurality of suction paths in communication with an external space and the vacuum chamber. The check valve forming unit includes a plurality of check valves each arranged at each of the suction paths.

In a vacuum suction device that includes a plurality of suction portions (suction pads) and is capable of sucking workpieces of various sizes, check valves (flow passage adjustment valves) may be disposed in respective paths that branch from a vacuum generator and reach the suction portions. By the action of the check valves, the vacuum pressure required for sucking the workpiece acts on the workpiece effectively. Also in a case where a large sponge pad including a large number of suction holes is used to suck workpieces of various sizes, it is desirable to dispose check valves as well.

However, in the vacuum suction device in which the check valves are disposed, the suction state of the workpiece cannot be easily confirmed by simply disposing the pressure sensor. This is because, since the vacuum pressure is maintained by the action of the check valves regardless of whether the workpiece is being sucked or is not being sucked, there is no difference between the pressures detected by the pressure sensor, and the state where the workpiece is being sucked and the state where the workpiece is not being sucked cannot be distinguished from each other.

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.

The suction pad according to the present invention has a structure in which the flow passage adjustment valves are disposed in the communication passages connecting the cavities of the sponge member to the negative pressure chamber, and includes the pressure detection port for detecting the pressure in at least one cavity of the sponge member. Therefore, it is possible to easily confirm whether or not the workpiece is being sucked.

A suction pad <NUM> according to a first embodiment of the present invention will be described with reference to <FIG>. As shown in <FIG>, the suction pad <NUM> includes a body <NUM> and a sponge member <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 is thick and covers the main body 12a from below. The main body 12a includes a suction port <NUM> connected to a vacuum generator (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 communication passages <NUM> communicating with the negative pressure chamber <NUM>.

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> includes a plurality of cavities <NUM> opening toward a workpiece W. The cavities <NUM> of the sponge member <NUM> communicate with the negative pressure chamber <NUM> through the communication passages <NUM> of the plate 12b. The sponge member <NUM> comes into contact with the workpiece W at a lower surface (bottom surface) <NUM> thereof.

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> exhibits flexibility which is a property of open cells until it is compressed by a predetermined amount from a natural state, and exhibits airtightness which is a property of closed cells after it is compressed by the predetermined amount.

The sponge member <NUM> can be deformed in accordance with the surface shape of the workpiece W by exhibiting flexibility. Even if the workpiece W has irregularities on its surface as in the case of a cardboard box in which beverage containers are packaged, no gap is generated between the sponge member <NUM> and the workpiece W. The sponge member <NUM> comes into close contact with the workpiece W and then exhibits airtightness to cause vacuum pressure required for sucking the workpiece W to act on the workpiece W.

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.

A flow passage adjustment valve <NUM> is arranged in the middle of each communication passage <NUM> of the body <NUM>. The flow passage adjustment valve <NUM> adjusts the flow passage area of the communication passage <NUM> in accordance with the suction state of the workpiece W. When the cavity <NUM> is closed by the workpiece W, the flow passage area of the communication passage <NUM> is sufficiently increased, and the pressure in the cavity <NUM> becomes equal to the pressure in the negative pressure chamber <NUM>. That is, when the cavity <NUM> is closed by the workpiece W, the same vacuum pressure as the vacuum pressure generated in the negative pressure chamber <NUM> is generated in the cavity <NUM>. When the cavity <NUM> is not closed by the workpiece W, the flow passage area of the communication passage <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.

A specific structural example of the flow passage adjustment valve <NUM> is shown in <FIG>. The flow passage adjustment valve <NUM> includes a first joint member <NUM>, a second joint member <NUM>, and a valve element <NUM>. The tubular valve element <NUM> is disposed inside the tubular first joint member <NUM>, and can be vertically displaced with respect to the first joint member <NUM>. The first joint member <NUM> is provided with a tapered seat portion <NUM> against which a head part <NUM> of the valve element <NUM> can abut. The tubular second joint member <NUM> is connected and fixed to the first joint member <NUM>. A stopper <NUM> capable of abutting against a lower end of the valve element <NUM> is attached to the second joint member <NUM>. By the valve element <NUM> abutting against the stopper <NUM>, downward displacement of the valve element <NUM> is regulated.

The head part <NUM> of the valve element <NUM> includes an orifice <NUM> at its center, and the orifice <NUM> communicates with an inner space <NUM> of the valve element <NUM>. A sidewall of the valve element <NUM> includes a plurality of openings <NUM> that communicate with the inner space <NUM> of the valve element <NUM>. The area of the opening <NUM> is sufficiently larger than the area of the orifice <NUM>. The inner space <NUM> of the valve element <NUM> communicates, at the lower end thereof, with an internal space of the second joint member <NUM>. A spring <NUM> for biasing the valve element <NUM> downward is disposed between the first joint member <NUM> and the valve element <NUM>.

In a state where the head part <NUM> of the valve element <NUM> is separated from the seat portion <NUM> of the first joint member <NUM>, an internal space of the first joint member <NUM> that is located above the seat portion <NUM> communicates with the inner space <NUM> of the valve element <NUM> via the orifice <NUM> and the plurality of openings <NUM> of the valve element <NUM>. In a state where the head part <NUM> of the valve element <NUM> is in abutment against the seat portion <NUM> of the first joint member <NUM>, the internal space of the first joint member <NUM> that is located above the seat portion <NUM> communicates with the inner space <NUM> of the valve element <NUM> only via the orifice <NUM> of the valve element <NUM>.

When vacuum pressure is generated in the negative pressure chamber <NUM> in a state where the cavity <NUM> is not closed by the workpiece W, air passes through the orifice <NUM> 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 <NUM>, and the head part <NUM> of the valve element <NUM> abuts against the seat portion <NUM> of the first joint member <NUM>. When the head part <NUM> of the valve element <NUM> abuts against the seat portion <NUM>, the flow passage area of the communication passage <NUM> decreases, and the flow velocity of the air passing through the orifice <NUM> further increases. As a result, the state where the head part <NUM> of the valve element <NUM> is in abutment against the seat portion <NUM> of the first joint member <NUM> is reliably maintained.

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

The suction pad <NUM> can suck workpieces W of various sizes. The pressure in the negative pressure chamber <NUM> of the body <NUM> does not increase even if the workpiece W is small enough to contact only a part of the bottom 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 W, the vacuum pressure generated in the negative pressure chamber <NUM> does not decrease due to the action of the flow passage adjustment valve <NUM>.

The body <NUM> includes a detection passage <NUM> for detecting the pressure in a predetermined cavity <NUM> of the sponge member <NUM>. The detection passage <NUM> is arranged for each of one or more selected cavities <NUM>. The detection passage <NUM> vertically passes through the negative pressure chamber <NUM> and extends from an upper surface to a lower surface of the body <NUM>, and a lower end of the detection passage <NUM> communicates with the corresponding cavity <NUM>. An upper end of each detection passage <NUM> forms a pressure detection port <NUM>. A pressure sensor <NUM> is individually connected to each pressure detection port <NUM>. The pressure in the selected cavity <NUM> is detected by the pressure sensor <NUM>.

Among the plurality of cavities <NUM>, the cavity <NUM> for which the detection passage <NUM> is correspondingly arranged is determined in consideration of the size of the workpiece W to be sucked. When the workpiece W of a predetermined size comes into contact with the sponge member <NUM>, the detection passages <NUM> are arranged corresponding to one or more cavities <NUM> closed by the workpiece W, and one or more cavities <NUM> that are not closed by the workpiece W. In order to explain the principle of the present invention using a simple drawing, <FIG> shows three cavities 22a to 22c. The detection passages <NUM> and the pressure sensors <NUM> are arranged corresponding to the cavity 22a and the cavity 22c among the three cavities.

Next, the operation of the suction pad <NUM> according to the present embodiment for sucking the workpiece W will be described. The suction pad <NUM> is used by being attached to, for example, a conveying device (not shown).

When a command for sucking the workpiece W placed on a floor surface or the like and conveying the workpiece W to a predetermined place is issued from a host controller (not shown) such as a PLC, the conveying device is driven and the suction pad <NUM> comes into contact with the workpiece W. At the same time or prior thereto, air in the negative pressure chamber <NUM> is sucked from the suction port <NUM> toward the vacuum generator. Although all the cavities <NUM> of the sponge member <NUM> are open to the atmosphere, the flow passage areas of the communication passages <NUM> are reduced by the flow passage adjustment valves <NUM>. Therefore, high vacuum pressure is easily generated in the negative pressure chamber <NUM>.

When a workpiece W1 having a small size comes into contact with a part of the bottom surface <NUM> of the sponge member <NUM>, one or some of the cavities <NUM> of the sponge member <NUM> are closed by the workpiece W1. Referring to <FIG>, the cavity 22a and the cavity 22b are closed by the workpiece W1, and the cavity 22c is not closed by the workpiece W1. The cavities 22a and 22b closed by the workpiece W1 communicate with the negative pressure chamber <NUM> through the communication passages <NUM> whose flow passage areas are sufficiently increased by the flow passage adjustment valves <NUM>. Therefore, the vacuum pressure generated in the negative pressure chamber <NUM> is directly transmitted to the cavities 22a and 22b and acts on an upper surface portion of the workpiece W1 that is in contact with the cavities 22a and 22b. Since the cavity 22c, which is not closed by the workpiece W1, communicates with the negative pressure chamber <NUM> through the communication passage <NUM> whose flow passage area is reduced, the vacuum pressure generated in the negative pressure chamber <NUM> does not decrease.

Due to the vacuum pressure generated in the negative pressure chamber <NUM>, an upward force (lifting force) acts on the workpiece W1. The lifting force is represented by ΔP·S, where ΔP represents a difference between the atmospheric pressure and the pressure in the negative pressure chamber <NUM>, and S is the total cross-sectional area of the cavities <NUM> closed by the workpiece W1. On the other hand, a downward force acting on the workpiece W1 is represented by (W + F), where W represents a weight of the workpiece W1 and F is a repulsive force caused by the compression of the sponge member <NUM>. The repulsive force F changes according to the compression amount of the sponge member <NUM>. When the sponge member <NUM> is compressed by a predetermined amount, ΔP·S = W + F is established. That is, the upward force and the downward force acting on the workpiece W1 are balanced, and the workpiece W1 is stably held by the suction pad <NUM>.

When a workpiece W2 having a large size comes into contact with the entire bottom surface <NUM> of the sponge member <NUM>, all the cavities <NUM> of the sponge member <NUM> are closed by the workpiece W2. Referring to <FIG>, the cavities 22a to 22c communicate with the negative pressure chamber <NUM> through the communication passages <NUM> whose flow passage areas are sufficiently increased by the flow passage adjustment valves <NUM>, and the vacuum pressure acts on an upper surface portion of the workpiece W2 that is in contact with the cavities 22a to 22c. As in the case of the workpiece W1 having a small size, the upward force and the downward force acting on the workpiece W2 are balanced, whereby the workpiece W2 is stably held by the suction pad <NUM>.

Next, a method of confirming the suction state of the workpiece W using the suction pad <NUM> according to the present embodiment will be described.

When the workpiece W1 having such a size that it contacts only a part of the bottom surface <NUM> of the sponge member <NUM> is being sucked, the vacuum pressure is detected by at least one of the pressure sensors <NUM> and the atmospheric pressure is detected by the remaining pressure sensors <NUM>. Referring to <FIG>, the pressure sensor <NUM> corresponding to the cavity 22a closed by the workpiece W1 indicates the vacuum pressure, and the pressure sensor <NUM> corresponding to the cavity 22c that is not closed by the workpiece W1 indicates the atmospheric pressure. On the other hand, when the workpiece W1 is not being sucked, the atmospheric pressure is detected by these pressure sensors <NUM>. Therefore, by monitoring the pressures detected by the respective pressure sensors <NUM>, it is possible to determine whether or not the workpiece W1 is being sucked.

When the workpiece W2 having such a size that it contacts the entire bottom surface <NUM> of the sponge member <NUM> is being sucked, the vacuum pressure is detected by all the pressure sensors <NUM>. Referring to <FIG>, both the pressure sensors <NUM> corresponding to the cavity 22a and the cavity 22c closed by the workpiece W2 indicate the vacuum pressure. On the other hand, when the workpiece W2 is not being sucked, the atmospheric pressure is detected by these pressure sensors <NUM>. Therefore, by monitoring the pressures detected by the respective pressure sensors <NUM>, it is possible to determine whether or not the workpiece W2 is being sucked.

If the plurality of pressure detection ports <NUM> are arranged efficiently, the suction state of the workpiece W can be accurately confirmed. <FIG> shows an example in which four pressure detection ports <NUM> are arranged near the centers of four sides of the upper surface of the body <NUM>. In particular, even if there is a variation in the position at which the workpiece W1 having a small size comes into contact with the bottom surface <NUM> of the sponge member <NUM>, there is a high probability that at least one of the four cavities <NUM> corresponding to these four pressure detection ports <NUM> is closed by the workpiece W1. That is, even if the accuracy of the suction position of the workpiece W with respect to the sponge member <NUM> is low, it is possible to easily confirm whether or not the workpiece W is being sucked.

The suction pad <NUM> according to the present embodiment includes flow passage adjustment valves <NUM> that adjust the flow passage areas of the communication passages <NUM> in accordance with the suction state of the workpiece W. Therefore, the vacuum pressure generated in the negative pressure chamber <NUM> can be caused to act, without being decreased, on an upper surface of the workpiece W that is in contact with the cavity (cavities) <NUM>. In addition, since the pressure detection ports <NUM> for detecting the pressure in one or more cavities <NUM> of the sponge member <NUM> are provided, it is possible to easily confirm whether or not the workpiece W is being sucked.

In the present embodiment, the detection passages <NUM> each vertically pass through the negative pressure chamber <NUM> and extend from the upper surface to the lower surface of the body <NUM>, but the configuration of each detection passage is not limited thereto as long as the detection passage communicates with the cavity <NUM>. For example, the detection passage may be branched from the communication passage <NUM> at a position lower than the flow passage adjustment valve <NUM> and opened to a side surface of the body <NUM> without passing through the negative pressure chamber <NUM>.

Further, in the present embodiment, the flow passage adjustment valves <NUM> are disposed in all of the communication passages <NUM>, but the flow passage adjustment valve <NUM> may not be disposed in some of the communication passages <NUM>. For example, the flow passage adjustment valve <NUM> may not be disposed in the communication passage <NUM> corresponding to the cavity <NUM> having a high probability of being closed by the workpiece W regardless of the size of the workpiece W. In this case, the detection passage <NUM> including the pressure detection port <NUM> may be disposed corresponding to only one cavity <NUM> for which the flow passage adjustment valve <NUM> is not disposed.

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

The detection passage <NUM> of the body <NUM> is arranged for each of a plurality of selected cavities <NUM>. The upper end of each detection passage <NUM> forms the pressure detection port <NUM>. The respective pressure detection ports <NUM> are connected to a common flow path <NUM> via check valves <NUM>, and a single pressure sensor <NUM> is connected to the common flow path <NUM>. That is, the common pressure sensor <NUM> is connected to the plurality of pressure detection ports <NUM> via the check valves <NUM>.

Claim 1:
A suction pad (<NUM>, <NUM>) comprising: a body (<NUM>); and a sponge member (<NUM>),
wherein the body (<NUM>) includes a negative pressure chamber (<NUM>), and a plurality of communication passages (<NUM>) configured to communicate with the negative pressure chamber (<NUM>), and the sponge member (<NUM>) includes a plurality of cavities (<NUM>) configured to open toward a workpiece and communicate with the negative pressure chamber (<NUM>) through the communication passages (<NUM>),
a flow passage adjustment valve (<NUM>) configured to adjust a flow passage area is disposed in each of the communication passages (<NUM>), and when vacuum pressure is generated in the negative pressure chamber (<NUM>) and a cavity among the plurality of cavities (<NUM>) is not closed by the workpiece, a flow passage area of a communication passage among the communication passages (<NUM>) that corresponds to the cavity that is not closed by the workpiece is adjusted to be decreased, and
the suction pad (<NUM>, <NUM>) further comprises a pressure detection port (<NUM>) configured to detect pressure in at least one cavity among the plurality of cavities (<NUM>),
the pressure detection port (<NUM>) is provided in plurality,
characterized in that
the body (<NUM>) includes a plurality of detection passages (<NUM>) configured to communicate with corresponding cavities (<NUM>) of the sponge member (<NUM>),
each of the detection passages (<NUM>) vertically passes through the body (<NUM>), and an end of each of the detection passages (<NUM>) forms each of the pressure detection ports (<NUM>), and
each of the pressure detection ports (<NUM>) is disposed near a center of each of four sides of an upper surface of the body (<NUM>).