Joints and connections – Having a cam – wedge – or tapered portion
Reexamination Certificate
1999-05-14
2001-08-21
Kim, Harry C. (Department: 3629)
Joints and connections
Having a cam, wedge, or tapered portion
C403S231000
Reexamination Certificate
active
06276867
ABSTRACT:
This invention relates to devices for forming a joint between two members and particularly, but not exclusively, to camming elements for such devices.
A known joint forming device disclosed in GB 2241299B comprises an elongate fastening element in the form of a metal pin which is secured to a major surface of one joint member and a rotatable metal camming element which is fitted to the other joint member. The camming element defines a centrally disposed cavity and an opening in its peripheral wall which allows a head portion of the pin to be inserted into the hollow region. A slot extends from the opening around the periphery of the camming element. The slot is sized to receive a neck portion of the pin such that the camming element can be rotated about its axis of rotation with the head inserted in the cavity. The camming element defines respective camming surfaces adjacent each side of the slot for engaging the head of the pin. The camming surfaces are adapted such that as the camming element is rotated in one direction, the pin is pulled longitudinally towards the axis of rotation of the camming element.
The camming surfaces of known camming elements typically have a lengthwise profile adapted to provide a two-phase tightening action.
FIG. 1
is a graph illustrating the relationship between rotation of the camming element and longitudinal movement of the fastening element in a conventional joint forming device and showing the two-phase tightening action. Longitudinal movement in mm is indicated along the vertical axis and rotation in degrees is indicated along the horizontal axis. In the first phase, a relatively “coarse movement” of the pin is provided by portions of the camming surfaces having a relatively steep, or tight, curve, i.e. a curvature adapted to provide a relatively large amount of longitudinal movement of the fastening element for a relatively small amount of rotation of the camming element. The relationship between the rotation of the camming element and the longitudinal movement caused is non-linear and is typically in excess of 0.5 mm for each 10° of rotation. This “coarse movement” is provided for closing a gap between the two panels and causing them to be pulled together, a movement often referred to as pull-up. The second phase of pin movement is caused by portions of the camming surfaces having a relatively flatter curve. The second-phase movement increases the compressive force on the joint and the reduced curvature of the camming surfaces imparts a degree of self-locking, often referred to as lock-up, to the joint forming device. It will be appreciated that the steeper the curve of the camming surfaces at the point of engagement with the head portion of the pin, the more likely it is that the camming element will back-off, i.e. rotate in the sense opposite to the sense in which it is rotated in order to tighten the joint when the panels are loaded in use. Accordingly, camming elements designed to provide the above-mentioned two-phase pin movement are intended to be rotated sufficiently during tightening of the joint to ensure engagement between the head portion of the pin and the flatter portions of the camming surfaces to obtain so-called lock-up.
In the use of the camming element which is the subject of
FIG. 1
, the camming element is rotated approximately 50 degrees from the position in which the head portion of the pin is inserted into the hollow region before the camming surfaces engage the head portion. The camming element must then be rotated a further 75 degrees before effective locking of the joint is obtained.
There are several disadvantages with these conventional joint forming devices and their camming elements.
One disadvantage is that relatively high turning forces are required to rotate the camming element during the pull-up phase. It will be appreciated that the cam is relatively highly ‘geared’ during the pull-up phase and the steeper the curve of the camming surfaces, the more torque input is required from the user. It is desirable to reduce the effort required of the user.
A further problem associated with this design is that in order to cope with the relatively high forces acting on it, the camming element must be heavily built. If the camming element is not made strong, it may burst under the loads imposed on it; the phenomenon of cam bursting will be familiar to those skilled in the art.
It will be appreciated that such camming elements are produced in vast quantities usually by means of diecasting techniques. Diecasting metals are relatively expensive and it is therefore desirable to reduce the weight of metal required for each camming element as much as possible without significantly reducing the strength thereof.
A further disadvantage of the known joint forming device is that it lacks tolerance. That is, if the recesses and bores in which the device parts are fitted are not made accurately, it may not be possible to form a reliable joint.
In more detail, in use the camming element is usually fitted into a recess in a major surface of a first joint member. This recess is communicated with the edge by means of a bore which extends from the recess to the edge. This arrangement allows the head portion of the pin to be inserted into the camming element so that it can be engaged by the camming surfaces on rotation of the camming element.
If the camming element is located too close to the edge of the joint member it may prove impossible to tighten the joint since only a small portion of the length of each camming surface will be effective on rotation of the tightening element. This results in very little pulling force being applied to the fastening element so that there is little compression in the joint and thus the joint is weak.
If the camming element is located too far away from the edge of the joint member, unless an undue amount of force is applied, it is only possible to obtain a small amount of rotation of the camming element in the tightening direction. In this case it is not usually possible to rotate the camming element sufficiently for the head portion to engage the portion of the cam which provides lock-up. The result is that there is no effective locking action and the camming element will tend to back-off if the joint is loaded which results in a weak joint.
It is an object of the invention to at least partially overcome the above-described problems.
The invention provides a camming element for a device for forming a joint between two members, the camming element comprising a body which has an axis of rotation and defines a generally centrally disposed cavity for receiving a head portion of an elongate fastening element, an opening through which said head portion can be inserted into said cavity and a slot extending from said opening about said body for receiving a neck portion of said fastening element when, in use, the camming element is rotated in one direction about said axis of rotation with said head portion received in said cavity, said body further defining at least one camming surface which is adapted for engaging said head portion and in the lengthwise direction thereof has an arcuate profile which is configured such that rotation of the camming element in said one direction causes longitudinal movement of said fastening element towards said axis of rotation and said slot being adapted to permit said rotation in said one direction through an angle of at least 190 degrees.
The invention also includes a camming element for a device for forming a joint between two members, the camming element having an axis of rotation and comprising at least one camming surface which in the lengthwise direction thereof has an arcuate profile, the or each said camming surface being arranged for engaging a head portion of an elongate fastening element such that rotation of the camming element in one direction causes longitudinal movement of the fastening element towards said axis of rotation and said arcuate profile being configured to provide a constant relationship between the amount of said longitudinal movement and said
Fitzpatrick ,Cella, Harper & Scinto
Kim Harry C.
Titus International PLC
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