1. Field of the Invention
This invention relates to ultrasonic horns for ultrasonic bonding of materials such as composite multiple-layer webs, and in particular, a method and system for directly measuring and controlling the amplitude of an ultrasonic horn during processing of the material being bonded.
2. Description of Prior Art
Ultrasonic bonders are known in the art. See, for example, U.S. Pat. No. 4,713,132 to Abel et al. which teaches a method and apparatus for ultrasonic bonding of a moving web, and U.S. Pat. No. 5,591,298 to Goodman et al. which teaches a machine for ultrasonic bonding utilizing a stationary ultrasonic horn. Stationary ultrasonic horn bonders are limited to operating on webs traveling at low speeds, in part, because, at higher web speeds, the web being bonded tends to pile up, or bunch up, at the leading edge of the stationary ultrasonic horn. In addition, the amplitude of a stationary ultrasonic horn during normal production of ultrasonically bonded materials is normally controllable only indirectly. Certain problems associated with material handling by stationary ultrasonic horn bonding equipment are addressed by U.S. Pat. No. 5,817,199 to Brennecke et al. which teaches the use of a rotating ultrasonic horn in combination with an anvil roll to ultrasonically bond web materials together. However, no method for directly controlling the amplitude of either a stationary or rotating ultrasonic horn during ultrasonic bonding of the web material is taught or suggested by the prior art known to me.
The use of light as a means for measuring the physical attributes of various types of objects is well known to those skilled in the art. For example, U.S. Pat. No. 4,046,477 to Kaule teaches an interferometric method and apparatus for sensing surface deformation of a workpiece subjected to acoustic energy in which the surface of the workpiece is illuminated by a laser beam which is reflected therefrom and passed through an optical beam splitter to produce a measuring beam portion and a reference beam portion. The measuring beam portion after reflection at a mirror is transmitted to photoelectric means while the reference beam portion is time delayed by means of an optical delay path and then brought to interfere with the measuring beam portion at the photoelectric means.
U.S. Pat. No. 3,918,816 to Foster et al. teaches a method and apparatus for dimensional inspection of a tire involving mounting of the tire for rotation and impinging on its tread surface a laser beam, analyzing the backscattered radiation to determine the position in space of the point of impingement, and selectably scanning or positioning the laser to measure various positions on the tire surface.
U.S. Pat. No. 4,086,808 to Camac et al. teaches a method and apparatus for measuring and monitoring vibrational or similar motion in mechanical elements in which retroreflectors on the elements are illuminated with monochromatic light, such as a laser, and the reflected beams form an interference pattern. Shifts in the interference fringes correspond to motion which changes the relative length of the paths of reflected light, and these shifts are counted or analyzed to monitor such motion.
U.S. Pat. No. 4,659,224 to Monchalin teaches the use of a laser beam and an interferometer of the confocal Fabry-Perot type for non-contact reception of ultrasonic waves wherein the interferometer detects the frequency shift caused by the Doppler effect in an incident layer beam as a result of ultrasonic deformations of a workpiece.
U.S. Pat. No. 4,619,529 to Iuchi et al. teaches an interferometric contact-free measuring method for sensing, by a laser beam, motional surface deformation of a workpiece subject to an ultrasonic vibration in which the laser beam is split into a measuring beam incident upon a measuring point on the workpiece and a reference beam incident upon a reference point close to the measuring point, and the two beams, after reflection, are brought into a common optical detector.
It is one object of this invention to provide a method for measuring the amplitude of stationary and rotating ultrasonic horns.
It is another object of this invention to provide a method for measuring the amplitude of stationary and rotating ultrasonic horns during production of an ultrasonically bonded web material.
It is a further object of this invention to provide a system for directly controlling the amplitude of stationary and rotating ultrasonic horns during ultrasonic bonding of a web material.
These and other objects of this invention are addressed by a system for directly controlling the amplitude of an ultrasonic horn comprising an ultrasonic horn, non-contact measurement means for directly measuring an amplitude of the ultrasonic horn, and control means for modulating the amplitude of the ultrasonic horn in communication with the non-contact measurement means. In accordance with one preferred embodiment of this invention, the non-contact measurement means comprises a non-contact amplitude sensor and a data acquisition and analysis system, which data acquisition and analysis system is operatively connected to the non-contact amplitude sensor and determines the amplitude of the ultrasonic horn.
A method for directly controlling the amplitude of an ultrasonic horn in accordance with this invention comprises the steps of detecting the surface motion of an ultrasonic horn with a non-contact amplitude sensor resulting in generation of a signal corresponding to said surface motion, transmitting said signal to a data acquisition and analysis system in which the signal is processed, resulting in a determination of the amplitude of the ultrasonic horn, transmitting said amplitude determination to an ultrasonic horn controller, and adjusting the amplitude of the ultrasonic horn to a desired level. In accordance with one preferred embodiment, the amplitude sensor is a high intensity light source from which a high intensity light beam is transmitted onto a surface of an ultrasonic horn, thereby generating a plurality of reflected light beams. A portion of the reflected light beams is passed through a lens, forming a light spot which is projected onto a detector. The detector produces an output signal proportional to the strength of the light spot and the location of the light spot on the detector. The displacement of the light spot on the detector is then determined. This displacement corresponds to the amplitude of the ultrasonic horn. In accordance with one particularly preferred embodiment, the ultrasonic horn is a rotating ultrasonic horn and the light source is disposed perpendicular to the axis of the rotation of the rotating ultrasonic horn.
A system for ultrasonic bonding in accordance with this invention comprises an ultrasonic horn in contact with a material to be bonded and non-contact means for measuring the amplitude of the ultrasonic horn. In accordance with one embodiment of this invention, the non-contact means comprises a light source which transmits a high intensity light beam onto a surface of the ultrasonic horn. A lens is positioned to receive a portion of the plurality of reflected light beams reflected off the surface and to project the portion of the plurality of reflected light beams as a light spot onto a detector positioned to detect the light spot. The detector produces an output signal proportional to the strength and location of the light spot on the detector. Translation means are provided for converting the displacement of the light spot on the detector into an actual horn displacement. In accordance with a preferred embodiment, the ultrasonic horn is a rotating ultrasonic horn and the light source is disposed perpendicular to the axis of rotation of the rotating ultrasonic horn.
In accordance with one embodiment of this invention, the non-contact amplitude sensor is another optical displacement sensor, of the fiber optic displacement sensor type, using a high intensity light beam, generally of non-coherent light, which relies on a change of the field of the emitter light beam as reflected off the moving, or displaced, surface of the horn to change the intensity of light received at the photodetector. Such fiber optic displacement sensors are commercially available, as from Mechanical Technology Inc. of Albany, N.Y.
In accordance with one embodiment of this invention, the non-contact amplitude sensor is a non-contact displacement measuring device employing an eddy current principle. In accordance with another embodiment of this invention, the non-contact amplitude sensor is a non-contact inductive measuring device. In accordance with yet another embodiment, the non-contact amplitude sensor is a non-contact capacitive displacement measuring device.