Bearings and supports

Details Bearings and supports Bearings and supports

1999-02-12

2001-07-17

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S323050, C310S323090, C310S323140, C310S323170

Reexamination Certificate

active

06262514

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates to machine components incorporating bearings, supports, guides and the like. It also describes the use of such components in a drive mechanism particularly applied to the control of elongate prismatic objects, such as wire electrodes for electro-discharge machining and rod electrodes for electro-discharge texturing.
BACKGROUND ART AND SUMMARY OF INVENTION
All drive mechanisms traditionally involve some form of bearing or support which serves to maintain the object in question in place by supporting its weight and/or constraining its movement along an appropriate path. Traditional bearings, supports and guides are characterized by static or dynamic errors such as backlash, hysteresis, dead zones, radial and axial play, vibration and stick-slip motion at low sliding velocities.
The present invention seeks to provide devices characterized by extremely high resolution and small time constant in which errors such as backlash, radial and axial play, dead zones and stick-slip motion at low sliding velocities are alleviated. The invention is also directed to the provision of a compact device that occupies little physical space and which can be manufactured at relatively low cost.
The applications of for which the invention is suited are many and varied. They include precision measuring systems for dimension and error control, multi-functional measuring devices and various types of supports for precision engineering, including devices used in superfinishing operations.
The applications which are at present most apparent to the applicant are electro-discharge machining (EDM) and electro-discharge texturing (EDT). In these operations, an electrode is placed a short distance from a workpiece and a high voltage is applied. As the distance is reduced, a spark will eventually be generated. This spark will erode the workpiece is the very localised area around the electrode tip. In EDM, a thin wire electrode is used, and the process can produce narrow holes in relatively hard electrically conductive materials to a significant depth. EDT is the term usually used to refer to texturing steel or aluminium rolls as a finishing operation to produce surface roughness on steel or aluminium sheet that is produced. Somewhat larger electrodes are used, in an array that is scanned over the surface of the roll in a spiral pattern, texturing the roll as it passes.
In both processes, the electrode is consumed and the position of what remains must therefore be continuously adjusted, as well as to accommodate the gradually receding workpiece. This is usually achieved by monitoring the electrical potential of the electrode relative to the workpiece. For example, if the nominal discharge voltage is V
0
, an electrode voltage of about 30% of V
0
indicates satisfactory machining. A drop to below 10% indicates a short circuit, meaning that the electrode must be raised relative to the workpiece. A rise to near 100% indicates an open circuit with no discharge taking place.
Existing EDM and EDT machines support the electrode by using bearings positioned near the workpiece so as to guide and support the tip. The electrode is held and moved by a servo means, which is large and of a significant mass in order to limit vibration. This inevitably introduces static and dynamic errors (backlash, hysteresis, dead zones, radial and axial play, vibration, etc.) and the classical approach to eliminating these is to increase the accuracy and stiffness of system elements. This sharply increases the cost of the devices. Further gains in accuracy of positioning is gradually reaching its economically acceptable limits.
Where multiple electrodes are required, such as in EDT and EDM as applied to the repeatable preparation of arrays of holes, existing machines simply attach a plurality of electrodes to a single servo. It has not hitherto been practical to move each electrode independently, since the massive servo is simply too large to duplicate in the space available. This means that the electrodes must be positioned according to the progress of the slowest electrode, with the majority of electrodes at any one time being at a non-ideal position. This is clearly undesirable.
This invention eliminates neither the servo nor the bearing, but integrates both into an active bearing by forming piezoelectric motors into the bearing structure. Thus, one or both elements are made from piezoelectric material or constitute part of a piezoelectric transducer.
This invention introduces the concept of active bearings, supports and guides, including fixed and moving elements which transmit forces from one to another, thereby to impart relative motion between the elements. This relative motion is achieved by transforming high frequency mechanical oscillations of one or both elements into continuous or step motion of the travelling element. Torque or forces are generated in the contact zone between both elements, which excludes errors, common to applications requiring external drives. In essence, the drive means is integrated into the bearing, this eliminating at a stroke the errors produced by interaction at that bearing.
Almost all machines include a driven member connected to a rotary drive member. The driven member must be supported, and hence a bearing or such is provided. The classical approach to reducing or eliminating static and dynamic errors of bearings, supports and guides (backlash, hysteresis, dead zones, radial and axial play, vibration, etc.) is to increase the accuracy and stiffness of system elements. This sharply increases the cost of the devices. Further gains in accuracy of high precision elements is gradually reaching its economically acceptable limits. The approach to this problem given here is to integrate a mechanical system with electronics and control. Further to reducing the cost and increasing the final accuracy, this alternative introduces new properties in the existing systems.
This invention eliminates neither the drive unit nor the bearing, but integrates both into an active bearing by forming piezoelectric motors into the bearing structure. Thus, one or both elements are made from piezoelectric material or constitute part of a piezoelectric transducer. To achieve rotation or translational motion, high frequency oscillations are generated in the contact zone between the two elements.
Thus, in one aspect the present invention provides a machine including a drive member and a driven member in mutual contact, the drive member including a transducer element comprising a piezoelectric element and a control means adapted to supply a signal to the piezoelectric element thereby to cause vibration thereof, wherein vibration of the piezoelectric element causes motion of the driven member relative to the drive member, and the driven member is at least predominantly supported by the transducer.
It is normally preferred if the driven member is wholly supported by the transducer. However, significant improvements can still be obtained even if only part of the weight thereof is supported.
The present invention also provides a machine including a drive member and a driven member in mutual contact, the drive member including a transducer element comprising a piezoelectric element and a control means adapted to supply a signal to the piezoelectric element thereby to cause vibration thereof, wherein vibration of the piezoelectric element causes motion of the driven member relative to the drive member, and movement of the driven member takes place along a route constrained by the transducer element.
The development of active bearings was made possible through the application of piezoactive materials and of various methods of transforming high frequency multi-component mechanical oscillations into continuous or step motion. An object of this invention is to integrate unique properties of piezoactive transducers and actuators (high resolution, low time constant, easy control of forms, types and parameters of oscillation, possibility to generate multi-component static, quasi-static and

Affiliated with

Also associated with

Rating

Bearings and supports does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bearings and supports, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bearings and supports will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2539276