WO2010088925A1

WO2010088925A1 - Suction gripper

Info

Publication number: WO2010088925A1
Application number: PCT/EP2009/000867
Authority: WO
Inventors: Timothy Vittor
Original assignee: Abb Ag
Priority date: 2009-02-07
Filing date: 2009-02-07
Publication date: 2010-08-12

Abstract

The invention is related to a suction gripper (10, 30, 40, 70) comprising a frame (14, 42) and a vacuum chamber (12, 46, 48) connected therewith. The vacuum chamber (12, 46, 48) is bordered at least on one side by a suction pad (16, 44, 78) and is foreseen to apply under-pressure therein. This side of the suction pad (16, 44, 78) facing off the vacuum chamber (12, 46, 48) is the gripping side (20). The suction pad (16, 44, 78) has at least in part a malleable structure permeable to air and the gripping side (20) of the suction pad (16, 44, 78) is covered at least in part by a membrane (82, 102) which provides suction holes (100). Air flow is enabled through the suction holes (100) of the membrane (82, 102) and through the suction pad (16, 44, 78) into the vacuum chamber (12, 46, 48) when an under-pressure is applied therein. At least one of those suction holes (100) is lockable and un-lockable for gas flow.

Description

Suction Gripper

Description

The invention relates to a suction gripper comprising a frame and a vacuum chamber connected therewith, whereas the vacuum chamber is bordered at least on one side by a suction pad and is foreseen to apply under-pressure therein, whereas this side of the suction pad facing off the vacuum chamber is the gripping side.

It is known, that in industrial production processes parts such as workpieces, components or modules have often to become assembled to a final product or unit. A typical example for this is the mounting together of smaller mechanical components but also the assembly of a car body. Such assembly processes are normally done automatically by machines comprising a gripper tool for grasping a part for example from a conveyor or a supply box and moving it into a desired position in relation to another part for mounting them together. Of course it is common, that several machines are involved in such an assembly process or that some of the production steps are done manually.

Especially in production lines for smaller units such as domestic appliances a wide range of different shaped parts have to be gripped. This often requires either a temporarily change of a gripper tool which requires effort and time or a reduction of the flexibility of the production system. According to the prior art, this problem is tried to be solved by a more flexible gripper tool.

In the patent application EP1916206 a suction gripper tool is disclosed, comprising a foam coating and an outer lining layer with suction holes. Due to an under-pressure which is applied on the rear side of the foam coating an object to be gripped is sucked to the outer lining layer on the front side. Such a suction gripper is more flexible concerning the shape of workpieces to be gripped because of the soft structure of the foam coating. Disadvantageously in this state of the art is that the gripping effect in between the suction gripper and workpiece to be gripped strongly depends on the size of the workpiece to be gripped. The gripping effect is as higher as lower the under pressure is. Especially workpieces which are significant smaller than the active gripping surface of the gripper will cause a degradation of the under-pressure so that the gripping effect will decrease for relative smaller workpieces.

Based on this state of the art it is the objective of the invention to provide an improved suction gripper tool of high flexibility which avoids the disadvantages mentioned above.

This problem is solved by a suction gripper of the aforementioned kind, which is characterized in that the suction has at least in part a malleable structure permeable to air, that the gripping side of the suction pad is covered at least in part by a membrane which provides suction holes so that a gas flow through the suction holes of the membrane and through the suction pad into the vacuum chamber is enabled when an under-pressure is applied therein and that at least one of those suction holes is lockable and un-lockable for gas flow.

By selectively locking those suction holes which have no contact to the surface of the gripped workpiece additional airflow through the membrane and through the suction pad into the vacuum chamber will be significantly reduced. Therefore the remaining airflow will mainly be caused by some partly unavoidable leakages of those suction holes which have contact to the surface, independent on the size of the workpiece in relation to the size of the gripping side. The consequence is a higher under pressure so that the gripping effect of the unlocked gripping holes is advantageously increased.

Preferably the suction gripper is moved over the workpiece to be gripped before applying under pressure on the vacuum chamber. In this case all suction holes are open. Then in the final gripping position the suction pad and the surface of the object to be gripped are in contact whereas the suction pad is preferably already deformed according to the shape of the workpiece at least in part. Then an under pressure is applied on the vacuum chamber. Air flow through the suction holes with contact to the workpiece should only be based on some minor leakage in the connection in between them. Through the other suction holes airflow will raise which is a trigger criterion to selectively lock those holes. A criterion for unlocking the suction holes and to bring all holes in the unlocked state could be for example the applying of an over pressure in the vacuum chamber.

In a preferred variant of the invention at least one suction hole is lockable and un- lockable by a related self-regulating mechanical locking device. This locking device could comprise for example a flap, which extends in the open state into the air flow channel of a suction hole. Due to mechanical or magnetic force it is stable in both positions, whereas a force is required to bring it from one position to the other and back. The transition in between both positions could be similar to a snap process. Trigger criterion to lock a suction hole could be an airflow through the suction hole based on an under pressure in the vacuum chamber. Since the flap extends into the flow channel of the air a force is applied on the flap so that it goes self-regulated into the closed state. An unlocking of the suction holes could be done by applying an over pressure into the vacuum chamber. Of course also other mechanism for a self- regulating locking device is thinkable, for example due the individual mechanical pressure on the membrane.

In another variant of the invention at least one suction hole is lockable and un- lockable by a related specifically switchable locking device. This could by for example a magnetic actuated valve, which can be triggered for example by some pre- processed measurement signals of force or temperature. The measurement sensors could be distributed across the whole membrane and related to one or more locking devices each.

It is also thinkable that one locking device is related to more than one suction holes, so that the suction pad is lockable and unlockable areawise.

In another embodiment of the invention a suction cup each is assigned to at least some of the suction holes. Such a suction cup improves the air-sealed connection in between suction hole and surface of the workpiece to be gripped, so that in the gripped state of the workpiece the under pressure will be higher and the gripping ef- feet better. The suction cup can be integrated into the membrane also in a sunken manner.

In a further variant exactly one locking device each is integrated in exactly one related suction cup. This reduces the effort for manufacturing a membrane with suction cups

According to another embodiment of the invention a truss structure permeable to air is connected with the suction pad, preferably located on the side of the suction pad bordering to the vacuum chamber. The suction pad might be mounted or glued thereon so that its mechanical structure is improved.

According to a further variant of the invention this truss structure permeable to air is at least in sections predominately made of a shape memory polymer, so that its basic shape is adjustable. Shape memory polymers are a known material. They are characterized that they return to an initial shape when heated to a certain temperature such as 60⁰C - 70⁰C. Then they are adjustable into a preferred shape which they permanently hold after cooling down. The flexibility of the gripper tool will be increased once more by temporarily adjusting the truss structure to the shape of a workpiece to be gripped.

In another embodiment of the invention the suction pad is moveable connected with the vacuum chamber. So it is possible to adjust the mechanical pressure of the suction pad on the workpiece before applying the under pressure. The deformation of the suction pad and thereby the gripping can be improved by this. A similar effect is obtained in that the whole vacuum chamber is moveable connected with the frame.

In a preferred variant of the invention at least one gripper finger is connected with the frame, so that the workpiece can be pre-gripped with for example two gripper fingers, so that a higher pressure of the suction pad on the workpiece can be applied before starting the suction process. Due to the higher pressure the deformation of the suction pad is improvable so that the gripping effect of the suction is higher. After starting the suction process the workpiece might be released by the gripper fingers. In a certain embodiment sensors are foreseen for the sectional determining of a pressure on the membrane respectively the suction cups which can be used for example for the selective triggering of related locking devices.

In a preferred embodiment the gripper tool is mounted on a robot. Industrial robots with for example 6 or 7 degrees of freedom in movement are very flexible machines to move the gripper tool from one position to another. So the combination of gripper tool and robot is very suitable for industrial production lines.

Further advantageous embodiments of the invention are mentioned in the dependent claims.

The invention will now be further explained by means of an exemplary embodiment and with reference to the accompanying drawings, in which:

Figure 1 shows a first suction gripper in a status before gripping,

Figure 2 shows a first suction gripper in a status with gripped workpiece,

Figure 3 shows a second suction gripper,

Figure 4 shows a third suction gripper and

Figure 5 shows asuction cup in open (A), intermediate (B) and closed (C) state

Fig. 1 shows a cross-section of a first suction gripper in a status before gripping. The suction gripper comprises a rectangular first frame 14 and a vacuum chamber 12 located therein. The vacuum chamber 14 is limited on five sides by the frame 14, respectively it is build by the frame 14 itself. The 6^th side of the vacuum chamber 14 is bordered by the side 18 of the first suction pad 16. Of course an air permeable truss structure can be foreseen on which the suction pad 18 is mounted.

It is possible to apply an under pressure within the vacuum chamber 14 by sucking out the air inside, which is shown with the arrow 24. This under-pressure causes also airflow 26 through the suction pad 16. The gripping side 20 of the suction pad 16 is covered by a membrane, which is not shown in detail in this fig. and which comprises several preferably equally spaced suction holes. This membrane is preferably not or at least less air permeable, so that the main airflow 26 goes through the suction holes of the membrane and then through the suction pad 16. The suction pad 16 itself is made at least in part of a flexible, soft and air permeable material. This material has either a homogeneous and porous structure or some dedicated channels or holes can be foreseen within its structure. Also a combination of both is possible.

Under the gripping side 20 of the gripper tool 10 a first workpiece is shown.

Fig. 2 shows the same gripper tool with the gripped workpiece. Due to the soft structure the workpiece was moveable partly into the suction pad so that the suction pad has been deformed. The non-linear top surface of the workpiece is now covered by the deformed suction pad. In the ideal case, the contact in between the gripper side of the suction pad and the surface of the object is as good, that all holes of the membrane are closed by the sucked surface of the workpiece. Then the airflow 32 out of the vacuum chamber is theoretically zero, because no air can flow into the vacuum chamber through the suction pad.

In the real case several suction holes will remain, which are not covered by the surface of the object, so that a reduced permanent airflow will be caused if the membrane is not according to the invention. Also suction holes which are not 100% sealed by the surface of the workpiece might cause some leakages so that additional airflow will rise. This reduced airflow is shown with the arrow 32. Another consequence of the airflow 32 is, that the under pressure within the vacuum chamber will be reduced, so that the gripping effect becomes worse.

To avoid this negative influence, each of the not shown holes in the membrane can be locked and un-locked by a dedicated locking mechanism. A locking of those suction holes, which have no contact to the surface of the workpiece, reduces the airflow 32 significantly, so that the under pressure becomes higher within the vacuum chamber and the gripping effect becomes better by this reason. The locking mechanism and its triggering are explained in detail in fig. 5.

Fig. 3 shows a cross section of a second suction gripper 40 with a second frame 42, a second suction pad 44, and a first 46 and second 48 part of the second vacuum chamber. In comparison to the first gripper tool shown in the previous figs, the second suction pad 44 is wider and thicker. Due to the increased thickness it is more deformable, so that it is more flexible concerning different shaped workpieces. To prevent airflow through the sides, a special and non air permeable membrane is foreseen for the bordering 50 of the sides. The suction pad 44 is mounted or glued on the truss structure of a piston 54. The piston is air-sealed against the vacuum chamber 46, 48 and moveable up and down. This enables the influencing of the pressure of the suction pad 44 on the workpiece 60 especially when the workpiece is in contact with the suction pad but not yet gripped. So the deformation of the suction pad while suction gripping can be optimized in that way, that the contact in between suction pad and surface of the workpiece is as good and sealed as possible.

An under pressure is applied within the vacuum chamber 46, 48 by sucking out air. In the status of under-pressure the gas flow 58 is rather low and consists from the air coming in to some leakages of not 100% sealed holes, whereas all suction holes without contact to the surface of the workpiece 60 are automatically closed according to the invention. In this example the suction pad 44, the piston with truss structure 54 and an intermediate wall 56 are one unit, which can be connected with the frame 42. So the vacuum chamber is divided in two parts, the first part as the hollow space within this unit and the second part as hollow space bordered by the second frame 42 and the intermediate wall of the unit. The intermediate wall is of course air permeable to ensure the inner air flow 56.

It is thinkable to build the truss structure with piston 54 at least in part out of a shape memory polymer so that an adaptation of the shape of the truss structure to the shape of the workpiece to be gripped can be done temporarily. The flexibility of the gripper tool becomes once again increased by this.

Figure 4 shows a cross section of a part of a third suction gripper 70. A third suction pad 78 is covered on its lower gripping side with a membrane 82, preferably comprising a rubber-like material. The membrane 82 comprises also several preferably equally spaced suction holes, for example in a square structure across the gripping surface in a distance of 1mm to 30mm each to each other. The diameter of the holes might amount for example 0.01 mm to 2mm and higher, whereas the size of the sue- tion pad depends on the maximum size of the workpieces to be gripped and might amount 30mm x 50mm and up to 500mm x 1000mm and higher. The thickness of the suction pad itself depends on the 3D shape of the different types of workpieces to be gripped and might amount from 10mm and less to 200mm and higher.

On each suction hole of the membrane a suction cup 72 respectively 74 is attached. Of course those suction cups and the membrane might be produced out of a single block of an elastic material. Due to its elastic structure, the suction cup improves the air proof sealing in between suction holes and belonging part of the surface to be gripped. The intermediate space 76 in between and membrane can also be reduced - in the extreme to zero - by arranging the suction cups deeper and sunken within the membrane itself. The suction first cups 72 have a suction contact to the third work- piece 80, whereas the second suction cups 74 don't have a contact to the third work- piece 80. After gripping the third workpiece 80 with the third suction pad 78 and the belonging components, all second suction cups 74 respectively the related suction holes have been closed to improve the gripping effect.

Fig. 5 finally shows a cross section of suction cup 92 on a membrane 102 in several locking states, whereas the suction cup 92 is located over a suction hole 100 of the membrane 102. At the edge between the suction cup and the membrane, a spring- elastic flap like, circular locking device 94 with an inner hole is arranged, which can be compared with a cardiac valve in the widest sense. Without influence of additional forces, such as a high air flow through the suction cup, this flap like device 94 has - due to the spring-elastic mechanism - an opening angle directing to the workpiece to be gripped.

In state A air 90 flows through the suction cup 92 and the suction hole 100. State B shows an intermediate position of the locking device 94, which is caused by an increased airflow 98. State C shows the locking device in the closed status, which is now hold due to the under pressure within the suction pad 78 respectively within the not shown vacuum chamber behind it.

The trigger criterion for locking the suction holes could be a high airflow through the suction hole 100, caused by an increased under pressure in the vacuum chamber after placing the gripper over the workpiece to be gripped. A trigger criterion for unlocking could be either a significantly reduced under pressure, it could be also an over pressure so that air is blown into the vacuum chamber. Therefore also a snap effect of the locking device based on mechanical or magnetic force for example is thinkable, so that it is in a stable state either in the locked or in the unlocked position, whereas a force is required to bring the locking device from one position to the other.

List of reference signs

first suction gripper before gripping first vacuum chamber first frame first suction pad side of first suction pad facing to vacuum chamber gripper side first workpiece first gas flow out of first vacuum chamber gas flow through first suction pad first suction gripper with gripped workpiece second gas flow out of first vacuum chamber second suction gripper second frame second suction pad first part of second vacuum chamber second part of second vacuum chamber bordering of first part of second vacuum chamber intermediate wall piston with truss structure gas flow through second suction pad and truss structure gas flow out of second vacuum chamber second workpiece third suction gripper first suction cups with contact to workpiece second suction cups with no contact to workpiece intermediate space third suction pad third workpiece first membrane suction cup in open (A), intermediate (B) and closed (C) state cross section through suction cup 94 locking device

96 gas flow through suction cup in open state

98 gas flow through suction cup in intermediate state

100 suction hole

102 second membrane

Claims

1. Suction gripper (10, 30, 40, 70) comprising a frame (14, 42) and a vacuum chamber (12, 46, 48) connected therewith, whereas the vacuum chamber (12, 46, 48) is bordered at least on one side by a suction pad (16, 44, 78) and is foreseen to apply under-pressure therein, whereas this side of the suction pad (16, 44, 78) facing off the vacuum chamber (12, 46, 48) is the gripping side (20), characterized in that the suction pad (16, 44, 78) has at least in part a malleable structure permeable to air, that the gripping side (20) of the suction pad (16, 44, 78) is covered at least in part by a membrane (82, 102) which provides suction holes (100) so that a gas flow through the suction holes (100) of the membrane (82) and through the suction pad (16, 44, 78) into the vacuum chamber (12, 46, 48) is enabled when an under-pressure is applied therein and that at least one of those suction holes (100) is lockable and un- lockable for gas flow.

2. Suction gripper according to claim 1 , characterized in that at least one suction hole (100) is lockable and un-lockable by a related self-regulating mechanical locking device (94).

3. Suction gripper according to claim 1 or claim 2, characterized in that at least one suction hole (100) is lockable and un-lockable by a related specifically switchable locking device.

4. Suction gripper according to claim 2 or claim 3, characterized in that the related locking device is assigned to at least two suction holes (100).

5. Suction gripper according to any of the previous claims, characterized in that a suction cup (72, 74, 90) each is assigned to at least some of the suction holes (100).

6. Suction gripper according to any of the previous claims, characterized in that exactly one locking device each is integrated in exactly one related suction cup (72, 74, 90).

7. Suction gripper according to any of the previous claims, characterized in that a truss structure (54) permeable to air is connected with the suction pad (16, 44, 78).

8. Suction gripper according to claim 7, characterized in that the truss structure (54) permeable to air is at least in sections predominately made of a shape memory polymer, so that its basic shape is adjustable.

9. Suction gripper according to any of the previous claims, characterized in that the suction pad (16, 44, 78) respectively the related truss structure (54) is moveable connected with the vacuum chamber (12, 46, 48).

10. Suction gripper according to any of the previous claims, characterized in that the vacuum chamber (12, 46, 48) is moveable connected with the frame (14, 42).

11. Suction gripper according to any of the previous claims, characterized in that at least one gripper finger is connected with the frame.

12. Suction gripper according to any of the previous claims, characterized in that sensors are foreseen for the sectional determining of a pressure on the membrane (82) respectively the suction cups (72, 74, 90).

13. Suction gripper according to any of the previous claims, characterized in that it is mounted on a robot.