WO2012143618A1

WO2012143618A1 - Vacuum gripper

Info

Publication number: WO2012143618A1
Application number: PCT/FI2012/050397
Authority: WO
Inventors: Matti Turulin; Jari Kiviniemi
Original assignee: Autoprod Oy
Current assignee: Autoprod Oy
Priority date: 2011-04-20
Filing date: 2012-04-20
Publication date: 2012-10-26
Anticipated expiration: 2013-10-20
Also published as: FI123181B; FI20115384A7; FI20115384A0

Abstract

There is a suction pad (14) in the vacuum gripper, an air flow passage leading from inside the suction pad to the outside of the suction pad and a shut-off valve (22) on the air flow passage. There is a cavity (44) in the shut-off valve and a spindle pin (50) arranged to move in the cavity, in which spindle pin there is a tubular hole (56) in the longitudinal direction of the spindle pin. The first end of the hole opens inside the suction pad and the opening (58) of the second end leads to the cavity. The spindle pin can be brought into a first position, in which the opening in the second end is closed and into a second position, in which the opening in the second end is open. The function of the shut-off valve is thus controlled with the position of the spindle pin. When the suction pad is moved against the surface of the object to be gripped, the surface of the object presses the end of the spindle pin and the spindle pin moves into the second position. An air flow passage opens from inside the suction pad to the outside of the suction pad, when the mouth of the suction pad is pressed against the surface of the object. The air pressure makes the spindle pin to move in the cavity into the first position that closes the air flow passage when the suction pad is not gripping the object, i.e. the surface of the object is not pressed against the first end of the spindle pin. The vacuum gripper is connected to a negative pressure source with a suction tube 24.

Description

Vacuum gripper

The object of the invention is a vacuum gripper, in which there is a suction pad, an air flow passage leading from inside the suction pad to the outside the suction pad and a shut-off valve in the air flow passage, in which shut-off valve there is a cavity and a closing member arranged to move in the cavity.

Devices meant for moving and processing of objects use commonly vacuum grippers in which there is a suction pad that is placed against the surface of the object. When air is sucked out from the inside of the suction pad, negative pressure is created inside the suction pad and the suction pad adheres to the surface of the object. Often the equipment comprises several vacuum grippers that are connected through connecting channels to a shared low-pressure chamber.

Several disadvantages are related to vacuum grippers according to prior art. If air is able to flow unobstructed through the suction channel of one of the grippers, the negative pressure diminishes immediately in all grippers connected to the same connect- ing channel and the adhesion of all the grippers deteriorates. Therefore the suction channel of an individual vacuum gripper must be able to be closed immediately after the suction pad detaches from the surface of the object. For example electrically guided magnetic valves can be used for the closing of the suction channels. The magnetic valves increase the production costs of vacuum grippers and the electric guidance they need makes the equipment complicated.

Documents DE 2146705 and WO 97/45355 present vacuum grippers in which the suction channel is closed either wholly or partly with the help of a ball, that is placed in the suction channel and which ball moves inside the suction channel by the influence of air pressure. Also gravity effects inevitably the movements of the ball, due to which the closing of the suction channel is unsure especially when the gripper is used in different, changing positions. Document FI20045382 presents a vacuum gripper in which a movable object is placed inside the vacuum channel together with a spring, with which spring forces are focused on said object. The shut-off valve implemented with the help of a spring functions unreliably in situations where the by-pass flow of air between the suction pad and the surface of the object can fluctuate considerably.

The object of the invention is to present a vacuum gripper with which defects and disadvantages associated with prior art can be reduced. The objects according to the invention are achieved with a vacuum gripper that is characterised by what is presented in the independent claim. Some advantageous embodiments of the invention are presented in the dependent claims.

The object of the invention is a vacuum gripper, in which there is a suction pad, an air flow passage leading from inside the suction pad to the outside of the suction pad, and a shut-off valve in the flow passage of the air. There is a cavity and a closing member arranged to move in the cavity in the shut-off valve. Said shut-off member in the invention is a spindle pin, in which there is a tubular hole. In the hole, there is a first end, which opens inside the suction pad and a second end, in which there is an opening leading inside the cavity. The spindle pin can be brought into a first position, in which the opening in said second end is closed and into a second position, in which the opening in said second end is open. When the opening in the second end of the spindle pin is closed, the air flow passage from inside the suction pad to the outside of the suction pad is closed. Respectively, when the opening in the second end is open also the air flow passage from inside the suction pad to the outside of the suction pad is open. The functions of the shut-off valve are thus regulated with the help of the position of the spindle pin.

In a preferred embodiment of the vacuum gripper according to the invention, the opening in the second end of the spindle pin is arranged to open against the wall of the cavity in said first position of the spindle pin. Then the wall of the cavity closes the opening completely and air cannot flow through the opening into the cavity.

In a second preferred embodiment of the vacuum gripper according to the invention, the opening in the second end of the spindle pin is arranged to open into the space defined by the walls of the cavity in said second position of the spindle pin. Then air flows unobstructed from the opening into the cavity.

In a third preferred embodiment of the vacuum gripper according to the invention, the spindle pin is an elongated part that is movable in the longitudinal direction of the cavity.

In a fourth preferred embodiment of the vacuum gripper according to the invention, there is a first end in the spindle pin extending inside the suction pad and the spindle pin can be moved into said second position by focusing force in the longitudinal direction of the spindle pin to the first end of the spindle pin. When the suction pad is moved against the surface of the object to be gripped, the surface of the object presses the end of the spindle pin and the spindle pin moves into the second position. In other words a flow passage of air is opened from the inside of the suction pad to the outside of the suction pad when the opening of the suction pad is pressed against the surface of the object.

In a fifth preferred embodiment of the vacuum gripper according to the invention the surface area Ai of the first end of the spindle pin is substantially smaller than the surface area A₂ of the second end of the spindle pin and both ends are in contact with the air surrounding the vacuum gripper. Thus equal air pressure affects both ends of the spindle pin. Since the surface area of the second end is substantially larger than the surface area of the first end, a greater force is directed at it. Thus air pressure forces the spindle pin to move in the cavity towards the suction pad when the suction pad is not gripping the object, i.e. the surface of the object is not pressed against the first end of the spindle pin. In a sixth preferred embodiment of the vacuum gripper according to the invention there is a closing surface with a conical shape between the first end and the second end of the spindle pin and there is a gasket surface with a substantially same shape as the closing surface in the wall of the cavity. In the first position of the spindle pin the closing surface is against the gasket surface of the cavity and in the second posi- tion of the spindle pin the closing surface and the gasket surface are apart from each other. With a compatible shape of the closing surface and the gasket surface it is ensured that in the first position of the spindle pin the spindle pin closes the cavity completely i.e. air is not able to flow through the gap between the closing surface and the gasket surface. In a sixth preferred embodiment of the vacuum gripper according to the invention the length of the spindle pin is adjustable. The length of the spindle pin and especially the length of the portion of the spindle pin that extends inside the vacuum gripper influence the stage in which the spindle pin moves from the first position into the second position, in other words when the air flow passage from inside suction pad to the out- side of the suction pad opens. The gripping susceptibility of the vacuum gripper can be regulated by adjusting the length of the spindle pin. In a seventh preferred embodiment of the vacuum gripper according to the invention there is a housing, in which there is a through hole into which the shut-off valve is fitted. The shut-off valve is thus a separate part which is placed inside the housing.

In an eight preferred embodiment of the vacuum gripper according to the invention there is a suction tube to be connected to a negative pressure source. With the help of the negative pressure source air can be sucked out of the vacuum gripper, whereupon the vacuum gripper adheres to the object.

An advantage of the invention is that it functions with the same reliability in all positions in which the vacuum gripper is used. Further advantage of the invention is that several vacuum gripper can be connected to the same negative pressure circuit without electrical components.

Another advantage of the invention is that it is structurally simple and functions reliably.

In the following, the invention is described in detail. In the description reference is made to the accompanying figures, in which

Figure 1a presents by way of an example a vacuum gripper according to the invention depicted from the side,

Figure 1b presents by way of an example the vacuum gripper of Figure 1a depicted from the front and Figures 2a and 2b present the vacuum gripper of Figures 1a and 1b as cross- section figures.

In Figure 1a, a vacuum gripper according to the invention is presented by way of an example as depicted from the side, and in Figure 1b, the same gripper is presented from the front, from the direction of the suction pad. In the vacuum gripper there is a boxlike housing 10, on the first side of which there is a cylindrical recess 12 (Figure 1b). Inside the recess there is a suction pad 14, the first edge 16 of which extends outside the recess. The second edge of the suction pad is attached to the bottom 20 of the recess (Figure 2a) and into the shut-off valve 22 in the bottom. There is a suction tube 24 on one side of the housing, through which suction tube air is sucked out from inside the suction pad. The suction pad is attached via suction tubes to the negative pressure source, for example to a vacuum tank (the vacuum tubes and the suction tube are not presented in the figures).

Figures 2a and 2b present by way of an example a vacuum gripper according to the invention as cross-section figures. Figure 2a presents a vacuum gripper detached from an object and Figure 2b presents the same vacuum gripper attached to the object 100. There is a through hole 26 in the bottom 20 of the recess 12 in the housing 10, which extends from the bottom of the recess to the second side of the housing. In the hole there is a first portion 28 opening to the second side of the housing, the radi- us of which first portion is and a second portion 30 opening to the bottom of the recess, the radius of which second portion is R₂. The radius R₂ of the second portion is bigger than the radius Ri of the first portion. In the joint of the first and second portion, there is a ring shaped rebate 32. A shut-off valve 22 is placed in the hole 26.

The shape of the outer surface of the shut-off valve corresponds substantially to the shape of the inner surface of the hole 26 in such a way that only the tolerance needed in the placing of the shut-off valve in its place remains between the outer surface of the shut-off valve fitted in the hole and the inner surface of the hole. There a cylindrical projection 34 on the first end of the shut-off valve, which projection is fitted into an opening on the surface of the suction pad 14 placed against the bottom 20. There is a sleeve 36 on the second end of the shut-off valve, which sleeve is fitted in the first portion of the hole 26. Between the projection and the sleeve there is a middle part of the shut-off valve, which is inside the hole 26 at the second portion. Around the middle part, there are two gasket rings, of which the first gasket ring 40a is on the sleeve side edge of the middle part and the second gasket ring 40b is near the edge of the side of the projection of the middle part. On the outer surface of the middle part between the gasket rings there is a groove 42 that runs around the middle part. The tolerance between the outer surface of the middle part and the inner surface of the hole 26 is sealed airtightly with the help of the gasket rings from both sides of the groove. There is third gasket ring 40c surrounding the projection in the joint of the projection and the middle part, which gasket ring seals the gap between the suction pad and the projection airtightly.

There is a cavity 44 penetrating the shut-off valve, the first end of which cavity, with a smaller diameter, runs through the projection 34 and opens inside the suction pad and a second end of which cavity, with a bigger diameter, opens into a sleeve 36. There is a portion between the first end and the second end in which there is a conical shape on the inner surface of the cavity. This conical portion of the inner surface of the cavity is called in this presentation as a gasket surface 46. Inside the cavity there is a spindle pin 50, in which there is a first end with a smaller diameter, the area of which end is A₁ and a second end with a bigger diameter, the area of which end is A2. The outer diameter of the first end is substantially equal to the inner diameter of the first end of the cavity and the outer diameter of the second end is substantially equal to the inner diameter of the second end of the cavity. There is a closing surface 54 on the area between the first and second end, at which closing surface the diameter of the spindle pin tapers. The conical shape of the closing surface is substantially the same as the shape of the gasket surface 46 of the cavity. In the middle of the spindle pin, there is a hole 56 in the direction of its longitudinal axel, the first end of which hole opens to the end surface of the spindle pins first end and the second end of which hole extends inside the spindle pin approximately to the conical closing surface of the spindle pin. On the first end of the hole there is an opening 57 that opens to the outer surface of the spindle pin and on the second end, there is an opening 58 that opens to the outer surface of the spindle pin.

There are air holes 52 in the wall of the middle part of the shut-off valve, the first end of which holes open inside the cavity's end with the bigger diameter near the gasket surface and the second end opens into the groove 42 on the outer surface of the middle part. Channel 60 leads through the wall of housing 10, the first end of which channel opens into the outer surface of the housing and the second end opens into the second portion 30 of hole 26 between the first and second gasket ring. Suction tube 24 is the extension of the first end of channel 60.

Figure 2a presents a vacuum gripper according to the invention in a situation where the suction pad 14 of the vacuum gripper is free, i.e. the suction pad is not pressed against the surface of any object. In this position the walls of the suction pad settle freely into the position according to the form of the suction pad, wherewith the first edge of the suction pad projects slightly from the recess 12, i.e. the suction pad extends slightly outside the plane defined by the first side of the housing. In operational situations, the suction tube 24 of the vacuum gripper is connected to negative pressure source, with the help of which air is sucked out from the suction tube (the negative pressure source is not presented in the figure). Thus a negative pressure is ere- ated in the channel 60 and in the groove 42 surrounding the middle part of shut-off valve. Gasket rings 40a, 40b stop the air from flowing into this space with negative pressure through the gap between the outer wall of the shut-off valve and the inner surface of the hole 26. Both ends of the spindle pin are directly in contact with the air surrounding the vacuum gripper, whereupon they are influenced by the air pressure present at the location of the vacuum gripper. Since the area A₂ of the second end of the spindle pin is considerably bigger than the area At of the first end, the force of the air pressure directed at the second end is bigger than the one directed at the first end. Thus, the spindle pin is pressed inside the cavity 44 into the first position according to Figure 2a, in which position the closing surface 54 of the spindle pin is placed against the gasket surface 46 of the cavity. The opening 58 at the second end of the hole 56 opens thus against the wall of the cavity, whereupon air cannot flow through the hole inside the cavity. Further, the butt joint between the closing surface and the gasket surface is situated on the air flow passage between the opening 58 on the second end of the hole 56 and the air holes 52. This butt joint is substantially airtight, which stops the air from flowing through the joint surface. The joint between the outer surface of the second end of the spindle pin and the inner surface of the cavity is substantially airtight, which stops air from flowing into the channel through the second end of the spindle pin. Figure 2b presents a vacuum gripper according to the invention in a situation where an object 100 is gripped with the vacuum gripper. In the gripping situation, the vacuum gripper is moved towards the object so that the open mouth of the suction pad 14 is placed against the surface of the object 100. The suction pad gripper is moved so close the object that the first side of the housing is placed tightly against the surface of the object. The edges of the suction pad are thus collapsed into accordion folds and the free edge surface of the suction pad is placed substantially airtightly against the surface of the object. At the same time the spindle pin 50 moves in the cavity 44 away from the suction pad as the first end of the spindle pin presses against the surface of the object. The object which is gripped with the vacuum gripper thus pushes the spindle pin at the gripping stage into the second position according to the Figure 2b. In this second position of the spindle pin, a circular open space is created between the gasket surface 46 of the cavity and the closing surface 54 of the spindle pin, into which open space the opening 58 at the second end of the hole 56 in the spindle pin opens. Thus an air flow passage opens from inside the suction pad through openings 57, 58 and hole 56 into the cavity 44 and further from the cavity through air holes 52 into the channel 60. Since the channel is connected through a suction tube 24 to the negative pressure source, a negative pressure is created inside the suction pad, which negative pressure keeps the suction pad attached to the sur- face of the object.

The object is detached from the vacuum gripper by closing the air flow passage from the suction pad to the negative pressure source and letting air flow inside the suction pad, whereupon the negative pressure inside the suction pad is filled and the suction pad detaches. The closing of the air flow passage and the letting of air into the suc- tion pad can be done with the help of a shut-off valve arranged in the flow passage (the shut-off valve is not presented in the Figures).

In a preferred embodiment of the vacuum gripper according to the invention, the end of the spindle pin 50 extending inside the suction pad 14 is lengthwise adjustable. In this embodiment the closing and opening of the closing valve can be regulated by changing the length of the spindle pin.

In another preferred embodiment of the vacuum gripper according to the invention, there is a force directing member, which directs force on the second end of the spindle pin which is directed towards the first end of the spindle pin. With the force directing member it can be ensured that the spindle pin always moves into the first position presented by Figure 2a, when the suction pad is not placed against an object. Advantageously said force directing member is a coil spring arranged inside the sleeve 36.

In the foregoing some preferred embodiments of the vacuum gripper according to the invention are described. The invention is not restricted to the solutions described above, but the inventive idea can be applied in different ways within the scope of the claims.

Claims

1. A vacuum gripper, in which there is a suction pad (14), an air flow passage (57, 58, 56, 44, 52, 60, 24) leading from the inside of the suction pad to the outside the suction pad and a shut-off valve (22) in the air flow passage, in which shut-off valve there is a cavity (44) and a closing member arranged to move inside the cavity, characterised in that said closing member is a spindle pin (50), in which there is a tubular hole (56), in which hole there is a first end opening inside the suction pad and a second end, in which second end there is an opening (58) leading inside the cavity, which spindle pin can be placed in a first position, in which the opening in said second end is closed and into a second position, in which the opening in said second end is open.

2. A vacuum gripper according to claim 1 , characterised in that in said first position of the spindle pin (50), the opening (58) in the second end of the spindle pin is arranged to open against the wall of the cavity (44).

3. A vacuum gripper according to claim 1 or 2, characterised in that in said second position of the spindle pin (50), the opening (58) in the second end of the spindle pin is arranged to open into the space defined by the cavity (44) walls.

4. A vacuum gripper according to any of the claims 1-3, characterised in that the spindle pin (50) is an elongated part, which is movable in the longitudinal direction of the cavity (44).

5. A vacuum gripper according to any of the claims 1-4, characterised in that and in the spindle pin (50) there is a first end extending inside the suction pad (14) and the spindle pin is movable into the second position by directing force to the first end of the spindle pin in the longitudinal direction of the spindle pin.

6. A vacuum gripper according to any of the claims 1-5, characterised in that the area Ai of the first end of the spindle pin (50) is substantially smaller than the area A₂ of the second end of the spindle pin and both ends are in contact with the air surrounding the vacuum gripper.

7. A vacuum gripper according to any of the claims 1-6, characterised in that there is a conical closing surface (54) between the first and second end of the spindle pin (50) and in the wall of the cavity (44) there is a gasket surface (46) that has substantially the same shape as the closing surface and in said first position of the spindle pin, the closing surface is against the gasket surface and in said second position of the spindle pin, the closing surface and the gasket surface are apart from each other.

8. A vacuum gripper according to any claim 1-7, characterized in that the length of the spindle pin (50) can be adjusted.

9. A vacuum gripper according to any claim 1-8, characterized in that there is a housing (10), in which there is a through hole (26), into which hole the shut-off valve (22) is fitted.

10. A vacuum gripper according to any claim 1-9, characterized in that there is a suction tube (24) to be connected to the negative pressure source.