Handling: hand and hoist-line implements – Utilizing fluid pressure – Venturi effect
Reexamination Certificate
1999-07-29
2001-03-20
Kramer, Dean J. (Department: 3652)
Handling: hand and hoist-line implements
Utilizing fluid pressure
Venturi effect
Reexamination Certificate
active
06203083
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a pipette for gripping components by means of a vacuum, in particular when mounting components on printed circuit boards.
A pipette of this nature is known, for example, from German utility mode 94 06 244. According to this document, the pipette has a suction opening on its end surface or side which faces toward the component. The component can be sucked onto a bearing surface, which surrounds the suction opening, of the end side. The bearing surface forms part of an elastomeric bearing member which is inserted into the end side of a base body of the pipette and which projects slightly beyond the end side. The bearing member is designed as an O-ring which bears with a press fit against the inner wall of the base body. The O-ring improves the suction ability of the pipette, since it rests more securely against the surface of the component which has been sucked on than does a hard component.
Mounting of components on printed circuit boards increasingly involves the use of mounting machines which have a movable revolver head which accommodates, stores and transports the components, rotates them to their desired installation position, adjusts their position and deposits them on the printed circuit board. The various movement operations result in accelerations which are such that there is a risk of the position of the component changing with respect to the pipette. However the permissible position deviation is so small that such a change in position must be avoided at all costs. In particular, it is also necessary to keep the suction distance between the pipette and the component within tight tolerances, in order to allow the components to be picked up and set down without them being subject to shocks.
The deformability of the known O-ring is so high that such levels of accuracy cannot be reliably achieved. In particular, the centrifugal force of the components which have been sucked on in the radial direction, which force occurs when the revolver head rotates, may result in the O-ring, which has been pressed, becoming detached.
SUMMARY OF THE INVENTION
The invention is based on the object of increasing the positional accuracy and the reliability of mounting. The invention achieves this object in an improvement in a pipette having a base body with a suction opening surrounded by an elastomeric bearing member that projects slightly above a surface of the base body. The improvement is the base body surrounds the bearing member on all sides without play, except for the side facing toward a component to be gripped or picked up.
As a result of the bearing member being supported on all sides in the base body, the bearing member cannot be deformed to such an extent and is held more securely in the base body. The lower deformability of the bearing member reduces the elastic deviation of the component which has been sucked on, so that this component can be fixed in a more accurate lateral and vertical position with respect to the pipette. Moreover, the fact that the bearing member is clamped inside the base body on all sides reduces the risk of a change in position being caused by rotation or by the bearing member being torn out.
As a result of the base body surrounding the bearing member without any cavities, the base body is clamped so securely in the inserted area that it can only be subjected to at most slight deformation at its free surface.
The cross section of the bearing member with a thick base part and a thin bearing rib to form the bearing surface enables the bearing rib to be extremely weak in cross section, while the remainder of the bearing member may be of a stronger a design. Such a bearing member can be produced and inserted more easily in terms of manufacturing technology. Due to its small height, the bearing rib is only slightly deformed yet can nevertheless adapt to unevenness or inclined positions of the component. The correspondingly narrow bearing surface against the component reduces the adhesive action to such an extent that the component no longer sticks to the pipette after its has been placed onto the printed circuit board.
The semi-circular or arc-shaped cross section produces a particularly narrow linear contact between the component and the bearing rib.
The refinement of the bearing surface projecting beyond the end surface or side of the base body, reliably avoids hard impacts when the component is placed onto the printed circuit board.
The refinement of the base part of the bearing member being cast or molded in a receiving groove of the base body; produces uniform deformation conditions over the entire extent of the bearing member which is, the example, annular. As a result of the bearing member being molded in the groove, a secure connection and a highly accurate arrangement are achieved.
The rectangular cross section of receiving groove can be produced easily by injection-molding means and produces good adhesion properties with respect to the elastomeric bearing member. These adhesion properties are increased if the base body is reinforced, for example with glass fibers, the ends of which project slightly into the receiving groove, thus making it more difficult for the molded-in bearing member to be torn out. The flush alignment of the outside with the base body results in an optimum support for the bearing rib.
The support member of the bearing member has the result of increasing the supporting force with increasing deformation, so that the bearing ribs are subjected to less deformation and the position deviations of the component with respect to the pipette, in particular the vertical position of the component, can be kept within tighter tolerances. Moreover, the lower support surfaces result in secure contact between a component and the bearing rib even if the component has a convex surface.
The refinement of the support member and bearing member being a single piece allows the support member to be produced in a single operation, together with the bearing member, without additional sprue points.
As a result of the refinement of the support member having structure and cross-section similar to the bearing member and extending within the space enclosed by the bearing member, the advantages of the design of the bearing member are also utilized by the support member, in particular with regard to the deformation and adhesion conditions.
The refinement of the support member extending inward from the annular bearing member like a radial spoke results in advantageous casting conditions, in which the support webs can easily be branched off from the bearing member.
The support ribs which slope obliquely downward fit optimally to, for example, a component with a convex suction face. Thus, as the pressure increases, a contact area which continuously grows in achieved without there being any possibility of leakage along the outer bearing rib.
The invention is explained in more detail below with reference to an exemplary embodiment which is illustrated in the drawing.
REFERENCES:
patent: 4795548 (1989-01-01), Meinel et al.
patent: 4799722 (1989-01-01), Marzinotto
patent: 4828304 (1989-05-01), No et al.
patent: 4925225 (1990-05-01), Dost
patent: 5125152 (1992-06-01), Grasmueller et al.
patent: 5685513 (1997-11-01), Tsukushi
patent: 5882055 (1999-03-01), Smith
patent: 1196336 (1965-07-01), None
patent: 94 06 244 (1994-10-01), None
patent: 0 277 731 (1988-08-01), None
patent: 1230461 (1960-09-01), None
patent: 2248221 (1992-04-01), None
Patent Abstract of Japan for Japanese 04 007900 of Jan. 13, 1992.
Kramer Dean J.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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