Abstract:
The invention provides a novel jackhammer that utilizes ultrasonic and/or sonic vibrations as source of power. It is easy to operate and does not require extensive training, requiring substantially less physical capabilities from the user and thereby increasing the pool of potential operators. An important safety benefit is that it does not fracture resilient or compliant materials such as cable channels and conduits, tubing, plumbing, cabling and other embedded fixtures that may be encountered along the impact path. While the ultrasonic/sonic jackhammer of the invention is able to cut concrete and asphalt, it generates little back-propagated shocks or vibrations onto the mounting fixture, and can be operated from an automatic platform or robotic system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. provisional patent application Ser. No. 60/765,153, filed Feb. 3, 2006, which application is incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected to retain title. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to devices that utilize ultrasonic and/or sonic vibrations, and more specifically to devices that use such vibrations for impact, probing, analysis or exploration purposes. 
     BACKGROUND OF THE INVENTION 
     Jackhammers are often used to open up or fracture a hard surface, such as concrete cement and rock formations. They are widely used in construction sites for preparation work, demolition and removal of concrete slabs, bricks and rocks as well as conducting maintenance or repair of plumbing or electrical wiring by electrical utility companies. Conventional jackhammers, also called pneumatic hammers, use compressed air to drive a metal piston up and down inside a cylinder. As the piston moves downward, it pounds the drill bit in the distal direction and into the target surface, e.g., the pavement, before reversing its direction and moving upward. 
     There are many drawbacks associated with the use of a pneumatic jackhammer that limit its applications. One of these drawbacks is the enormous acoustic noise that makes its use outside normal work hours nearly prohibitive in residential neighborhoods. Another drawback involves the violent back-pulsations during the operation of a pneumatic jackhammer, which require large axial forces and large holding torques during operation. In addition, the back-pulsations that propagate into the hand and body of the operators can cause severe damage and pose serious work hazards. Reported incidents include the dislocation and extraction of dentures from the operators&#39; mouths. The cutting action by a pneumatic jackhammer is indiscriminate and every object it encounters along its path will be damaged. In utilities maintenance work, for example, this drawback becomes critical since it is imperative for workers to avoid damaging wires, plumbing conduits, reinforcement rebar and other fixtures. 
     These and other drawbacks such as high power consumption not only limit the conventional jackhammer&#39;s use in construction and utility maintenance, but also in medical surgeries, robotic operations, archeology, and geological explorations including space expeditions. Specifically for space expeditions, since many planets or other celestial bodies do not have as large an atmospheric pressure as is present on the Earth, it would be difficult to produce the type of pneumatic forces that are generated on the Earth to drive a conventional jackhammer. Therefore, the need for a new kind of jackhammer is widely felt across many industries and research fields. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus aimed at providing fracturing impact that spares flexible structures by the use of ultrasonic and sonic vibrations. In one aspect, the invention relates to an apparatus that includes a piezoelectric actuator configured to generate vibrations at a resonance ultrasonic frequency, and a solid impactor configured to be displaced by the vibrations generated by the piezoelectric actuator for causing structural breakage in a target. The actuator of the apparatus may include a backing and a piezoelectric stack that are held in compression by a mechanical element. The apparatus may further include one or more horns for amplifying the vibrations generated by the actuator. In an embodiment, at least a portion of the impactor tapers towards its distal end. 
     In one feature, the impactor is rigidly connected to the actuator such that the impactor vibrates at substantially the same ultrasonic frequency as the actuator, e.g., at a frequency between about 20 kHz and about 40 kHz. In one embodiment, the impactor is also interchangeable with at least another impactor. 
     In another feature, the apparatus of the invention also has a mass configured to oscillate between the actuator and the impactor, such that the impactor vibrates at a frequency lower than the ultrasonic frequency of the actuator, e.g., between about 5 kHz and about 10 kHz. 
     In still another feature, the housing that encloses the actuator remains substantially motionless during operation of the apparatus. 
     In one further feature, the apparatus of the invention further includes a sensor in physical contact with the impactor, the sensor configured to measure properties of an object in contact with the impactor. In one embodiment, the apparatus further includes a control system configured to receive signals from the sensor. 
     In a second aspect, the invention relates to an apparatus that includes an actuator configured to generate vibrations, an impactor configured to be displaced by the vibrations generated by the actuator, and a handle configured to remain substantially motionless during operation of the apparatus. In one embodiment, the actuator is configured to generate vibrations at an ultrasonic frequency, and the handle is rigidly connected to a nodal plane of the actuator. 
     In another aspect, the invention relates to an apparatus that includes: 
     a piezoelectric actuator configured to generate vibrations at an ultrasonic frequency; 
     an impactor; and 
     a mass configured to oscillate between the actuator and the impactor, the mass having a selected magnitude such that it causes the impactor to vibrate at a frequency lower than the ultrasonic frequency. 
     In one embodiment, the impactor vibrates at an operating frequency that is sonic. 
     The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. 
         FIG. 1  illustrates a perspective view of basic embodiment of the ultrasonic/sonic jackhammer according to the invention. 
         FIG. 2  illustrates a perspective view of an alternative embodiment of the invention where the handles are disposed at a more weight-balanced position. 
         FIG. 3  illustrates a cross-sectional view of the embodiment illustrated in  FIG. 1  along the lines  3 - 3 . 
         FIG. 4  illustrates a cross-sectional view of one embodiment of the ultrasonic/sonic jackhammer according to the invention, where a free-oscillating mass is utilized. 
         FIG. 5  is a cross-sectional view of part of the device showing schematically one way to configure the horn, the free-oscillating mass and the impactor, according to one embodiment of the invention. 
         FIG. 6  is a perspective view of one embodiment of the invention with multiple piezoelectric stacks. 
         FIG. 7A  is a perspective view of one embodiment of the invention with multiple horns. 
         FIG. 7B  is a perspective view of one embodiment of the invention with multiple input paths for the horn. 
         FIG. 8A  is a perspective view of a robotic system equipped with an apparatus of the invention. 
         FIG. 8B  is a close-up view of a portion of the robotic system of  FIG. 8A , showing the jackhammer system of the invention. 
         FIG. 9  is a perspective view of an envisioned application of the invention in space exploration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a new type of jackhammer that utilizes ultrasonic and/or sonic vibrations to power the impacting bit for fracturing relatively brittle surfaces such as rocks and concrete. The new jackhammer disclosed herein uses a hammering mechanism that fractures brittle structures without causing damage to embedded flexible/ductile materials and structures. Further, the new jackhammer generates minimal back-pulsation that propagates back onto the mounting fixture, and requires little axial force or holding torque. As a result, it enables uses in conjunction with lightweight platforms such as those provided by certain robots and rovers in space missions, and also eliminates risks of injury to the operator. The present invention provides embodiments where the handle or the casing of the jackhammer remains virtually vibration-free during operation. Furthermore, apparatuses of the invention are significantly quieter than pneumatic systems, allowing uses in residential areas even at late hours or weekends while minimally perturbing the neighborhood. In particular, the invention provides jackhammer embodiments that make sounds inaudible to ordinary human ears, i.e., of ultrasonic frequencies. 
     Referring to  FIG. 1 , a basic setup for the present invention is now described. In one embodiment, an ultrasonic/sonic apparatus  10  is provided as a new generation of jackhammer. The apparatus  10  includes an actuator  12  for pulse generation, and an impactor  14  at the distal end of the apparatus for fracturing a target. The actuator is an ultrasonic transducer that typically includes a backing (not shown), a piezoelectric stack  16  and a horn  18  that amplifies the displacement generated by the stack. The piezoelectric stack  16  is capable of generating vibrations at an ultrasonic frequency. According to one feature of the invention, a free-oscillating mass is optionally provided to oscillate between the actuator  12  and the impactor  14  in order to reduce the frequencies of impacts by the apparatus. In the particular embodiment illustrated in  FIG. 1 , the optional mass  30  resides inside a cylindrical housing  20 , but is not visible in  FIG. 1 . The impactor  14  is the part that delivers impact into the target. It can be made of any material with sufficient stiffness such as metals and ceramics, and can assume a variety of shapes such as those resembling a drilling bit. Typically, the impactor is solid. In a preferred embodiment, it resembles the shape of a chisel with sides tapering toward its distal extremity. A pair of handles  22  is optionally provided. In the embodiment shown in  FIG. 1 , the handles  22  are mounted to a housing  62  that encloses the piezoelectric stack  16 . 
       FIG. 2  illustrates an alternative embodiment where the piezoelectric stack  16 , which constitutes a large portion of the weight of the apparatus  10 , has been moved towards the middle of the apparatus  10  such that the handles  22  outside the stack are positioned at a more weight-balanced spot. As shown in  FIG. 2 , the horn  18  can include a tapering rod for effective amplification of the vibrations. 
     Referring to  FIG. 3  where a cross-sectional view of the apparatus  10  of the invention is provided, the actuator is driven at the resonance frequency of the piezoelectric stack  16 , and one or more stress bolts  24  hold the stack in compression to prevent fracture during operation. The power supply is not specifically shown here, and can be a battery or AC source. As is well known, a piezoelectric material can convert an applied electrical field into a mechanical change in dimension. For electric fields applied at high frequency, a piezoelectric material can produce a change in dimension (or a vibration) at a correspondingly high frequency. To operate large impactors, a high power piezoelectric actuator is used. The backing  26  helps to maintain forward propagation of vibrations generated by the actuator. The horn  18  amplifies the vibrations introduced by the stack  16  as long as the interface area between the stack  16  and the horn  18  is larger than the interface area between the horn  18  and the impactor  14 . To that end, the horn  18  is preferred to be stepped, but it can also be of other geometries including tapered or exponential. The stack  16 , the horn  18 , and the impactor  14  may be coupled to one another in any conventional manner. In one embodiment, the impactor  14  and the horn  18  are manufactured as one integral piece. The stack  16  comprises a plurality of piezoelectric segments each of which is disposed between two electrodes. The driving field may be applied as an electrical potential between the two electrodes disposed on each side of a piezoelectric segment. In this manner, an appreciable resultant response can be obtained using a relatively low potential across any individual piezoelectric segment. 
     In operation, the impactor  14  vibrates at ultrasonic or sonic frequencies. In an embodiment, the impactor  14  is rigidly connected to the horn  18 . As a result, it vibrates at substantially the same ultrasonic or sonic frequency as the actuator, e.g., between about 20 kHz and about 40 kHz. In another embodiment, the impactor  14  is connected to the horn  18  in a manner that the impactor can be removed and interchanged with another impactor. Impact delivered by the impactor tends to comprise a small displacement but at a higher frequency, and causes structure breakage in relatively brittle targets such as ice, bricks, and rocks. The impact does not cause substantial damage to relatively flexible or ductile structures including wood, plastic and metal structures. Neither does the impact hurt soft human tissues upon momentary contact. 
     Referring now to  FIG. 4 , according to one aspect of the invention, the ultrasonic apparatus  10  can also incorporate a free-oscillating mass  30  that bounces between the tip of the horn  18  and the chiseling impactor  14 . As a result, the impactor  14  vibrates at a frequency lower than the resonance frequency of the actuator, typically at sonic frequencies, although the mass and the impactor can be selected of sufficiently light-weight structures and the gap between the mass and the impactor fixed so that the impactor may still vibrates at an ultrasonic frequency albeit lower than the original one emitted by the actuator. In one embodiment, the impactor vibrates at an operating frequency between about 5 kHz and about 10 kHz. The impact of the free-oscillating mass creates stress pulses that propagate to the interface between the impactor and the target surface onto which the jackhammer is placed. The target, e.g., a rock, fractures in the impact location when its ultimate strain is exceeded at the rock/impactor interface. 
     U.S. Pat. No. 6,617,760 issued to Peterson et al. describes details regarding the free-oscillating mass and is incorporated herein by reference in its entirely. There are many ways to incorporate the free-oscillating mass between the ultrasonic actuator and the impactor. Referring to  FIG. 4 , the impactor  14  has a stem  32  that is slidingly inserted inside a bore  34  at the tip of the horn  18 . The free-oscillating mass  30  is a circular or an annular element resembling a donut with an opening to fit around the impactor stem  32 . The free-oscillating mass is therefore confined to oscillate along the impactor stem  32 . As another example, referring now to  FIG. 5 , the free-oscillating mass  30  in this case is solid and is disposed between the tip  35  of the horn  18  and the impactor  14 . Specifically, the horn tip  35  has a diameter larger than the portion  36  leading to the tip, and the stem of the impactor  14  has a cylindrical housing  38  that is topped with a shoulder  40  that makes the opening of the housing  38  smaller than the diameter of the horn tip  35  such that it won&#39;t slip out. As a result, the free-oscillating mass  30  is trapped in between the horn and the impactor. 
     Regardless whether the ultrasonic/sonic jackhammer uses the free-oscillating mass or not, it can use multiple piezoelectric stacks and/or multiple horns. Referring to  FIG. 6 , these multiple piezoelectric stacks, in this particular example, three of them ( 40   a ,  40   b  and  40   c ), are disposed side by side in between the backing  42  and the top portion  44  of the horn  46 . Two mechanical elements, e.g., stress bolts  48   a  and  48   b , span the same length and hold the stacks in compression. As described earlier, the horn  46  amplifies the power—in this case, by virtue of having a much wider cross sectional area on the top portion  44  than the rest of it. Each of the multiple piezoelectric stacks  40   a - 40   c  is substantially identical and, in operation, driven to vibrate at the same resonance frequency. The power of all the piezoelectric stacks is combined and transmitted to the impactor through the horn and the optional free-oscillating mass. 
       FIG. 7A  illustrates a multi-horn configuration with multiple input paths for the reception of ultrasonic vibrations. Specifically in the illustrated embodiment, three piezoelectric stacks ( 50   a ,  50   b  and  50   c ) are each compressed between a backing ( 52   a ,  52   b  and  52   c ) and a horn ( 54   a ,  54   b  and  54   c ) by a stress bolt ( 56   a ,  56   b  and  56   c ). All of the horns ( 54   a ,  54   b  and  54   c ) converge into a single impactor  58 , combining the energy from the multiple piezoelectric stacks ( 50   a ,  50   b  and  50   c ). Preferably, each horn is stepped to increase the impact.  FIG. 7B  illustrates another configuration that serves a similar purpose. In this case, a forked or branched horn is provided with multiple input energy paths (two of the four are labeled as  54   a  and  54   b ) that converge into one single output path  59 , before connecting to the impactor (not shown). Each fork ( 54   a ,  54   b  and so on) of the horn has a geometry similar to its counterpart in  FIG. 7A , and is stepped to amplify vibration generated upstream by the piezoelectric stacks ( 50   a ,  50   b  and so on). 
     As shown in  FIG. 7A , in one embodiment of the invention, all the horns ( 54   a - 54   c ) attach or contact the impactor  58  at a curved, upper surface of the impactor  58 . This curved surface orients various horns ( 54   a - 54   c ) to angle toward each other rather than to run parallel to each other. The energy from these horns ( 54   a - 54   c ), which are angled with respect to each other, combine inside the impactor  58 . As shown in  FIG. 7B , in another embodiment of the invention, each fork ( 54   a ,  54   b  and so on) of the forked or branched horn is angled relative to the others (rather than being oriented parallel to another fork). The multiple forks meet at an intersecting location, where power provided by each fork is combined with that of the others so as to flow through the remainder of the forked horn. 
     Referring back to  FIG. 4 , the ultrasonic actuator  12  has a nodal plane  60  where there is substantially no vibration when the actuator is being driven to vibrate at its resonance frequency. This can be understood by considering that at any instant, there are vibrations going in one direction on one side of the plane and vibrations going in the other direction on the other side and they cancel each other out at the nodal plane. This neutral nodal plane  60  is typically found in between the bottom of the piezoelectric stack  16  and the top of the horn  18 , or somewhere proximate. Referring back to  FIG. 1 , in a preferred embodiment, the outside housing  62  for the ultrasonic/sonic jackhammer is mounted to the actuator at its nodal plane  60  so that the housing remains substantially motionless even during operation. Handles  22  can be further affixed to the housing  62  so that the handles also remain substantially motionless during operation, eliminating potential hazard for the operator and enabling integration with lightweight platforms and robots. Of course, the handles can be affixed directly to the actuator, and as long as they are somehow rigidly connected to the nodal plane of the actuator, the handles will remain substantially motionless during operation. In addition, the attachment of handles to a nodal plane, or to a housing connected to the actuator at a nodal plane will eliminate the loss of energy associated with motion of the handles. If the handles do not move, no mechanical energy will flow through them to some object or some person holding the handles. 
     The ultrasonic/sonic jackhammer can be used to screen the drilling location benefiting from the inherent probing capability of the piezoelectric actuator to operate as a sounding mechanism and as a mechanical impedance analyzer. A variety of sensors  70  ( FIG. 3 ) can be embedded in or disposed on the impactor, i.e., in physical contact with the impactor, to measure mechanical and electrical properties of the object that is in contact with the impactor. A control system is used to receive signals from the sensors and to produce valuable information on the soil or rock that is being worked on. The jackhammer system can further incorporate remote sensors, such as one or more accelerometers positioned away from the point of contact by the impactor for analyzing elastic wave changes in the medium that is being worked on. U.S. Pat. No. 6,863,136 issued to Bar-Cohen et al. describes details of the use of sensors including the use of sensor ceramics in the ultrasonic actuator, and is incorporated herein by reference in its entirety. These probing capabilities and the ability to carry sensors on the impactor can be used to optimize the drilling or exploration plan and to conduct in-situ data acquisition and analysis. 
     Referring to  FIGS. 8A and 8B , since the new jackhammer  10  does not introduce major back propagated vibrations onto the mounting fixtures, it can be mounted onto a robotic arm  80  and operated automatically from a rover  82  in planetary in-situ tasks. This application is shown graphically in  FIG. 8A , with a close-up view of the jackhammer mounted on a robotic arm shown in  FIG. 8B . Specifically, the ultrasonic/sonic jackhammer is shown to be used for cleaving fresh surfaces of rocks. Another potential application for the new jackhammer  10  is future construction and development of infrastructures as shown graphically in  FIG. 9 . If men want to eventually inhabit planets such as Mars, the ability to construct underground water reservoirs, housing, roads, and whatever men are accustomed on the Earth is critical. Given the fact that the atmospheric pressure on Mars is about one hundredth of the level on earth it would be difficult to produce the type of pneumatic forces that are generated on earth, and the disclosed ultrasonic/sonic jackhammer offers an important alternative. 
     While the present invention has been particularly shown and described with reference to the structure and methods disclosed herein and as illustrated in the drawings, it is not confined to the details set forth and this invention is intended to cover any modifications and changes as may come within the scope and spirit of the following claims.