Patent Application
20070291382
The following description may be further understood with reference to the accompanying drawings in which:
The drawings are shown for illustrative purposes only.
Optical scanning applications typically require that a mirror be attached to a shaft of a motor either directly or indirectly. For example, clamp-like parts have been employed that function to support the mirror as well as to attach it to the shaft. Inseparable cradle-and-clamp designs that are built into or onto the mirror have also been employed. In some cases, the mirror is cemented into a transverse slot in the shaft or a mounting structure.
Although it is generally desirable to minimize mass and therefore inertia of a rotor and load assembly in a limited rotation motor system, applicant has discovered that a shape memory alloy may be used to provide effective removable fastening of a load onto a shaft without adversely affecting inertia in accordance with certain embodiments of the invention. Shape memory alloys, such as nickel titanium alloys (sometimes referred to as Nitinol after their discovery by the Naval Ordnance Laboratory in 1962), are known to provide changes in shape that are dependent on temperature. In general, such alloys may include for example, nickel titanium, nickel titanium niobium, nickel titanium iron, nickel aluminum, indium titanium, copper zinc, copper tin, copper aluminum nickel, gold cadmium, silver cadmium, iron platinum, manganese copper, iron manganese silicon, and further alloys of the above elements and combinations. Shape memory alloys typically change up to 5% in size when heated from a martensite (cooled) condition to an austenite (heated) condition. Although shape memory materials have been used and suggested for applications in medical devices, electrical conductors, fasteners and shaft mounted components, such materials have not be used for limited rotation motors where the bond strength versus inertia tradeoff has been considered too demanding for such a fastener.
Applicant has discovered, however, that combining the use of a shape memory material with a tapered mounting structure provides limited rotation motor systems with improved bandwidth. It is generally desirable that the mirror be attached in a way that permits easy assembly and/or removal. This is necessary to ease system assembly and alignment, and also to accommodate replacement of the mirror with one of a different size or reflectivity range, or to allow replacement of a damaged mirror in situ. The mounting means must also assure proper geometrical alignment of the mirror as mounted to the shaft, at least in the direction normal to the mirror surface. It is of important that the inertia of the mount itself not compromise the performance of the system in dynamic applications, and be robust in proportion to the shock and vibrational environment of static systems.
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Different applications may require different degrees of locking of the taper versus the collar. For example, it might be desired that the direction perpendicular to the face of the mirror be hand-re-adjustable with respect to the angular position of the shaft during assembly and alignment of the optical system of which it is a part prior to heating of the collar to room temperature. This application would result in a relatively large taper angle. If the application, on the other hand, required that the optical system of which it is a part must withstand large accelerations, such as those during launch of a space vehicle, a relatively small taper angle may be used.
The angle of taper and length of engagement are chosen over a range of angles and lengths as a compromise between the need for a self-locking fit, and the desire for easy release when required. The size and materials for the shape memory alloy may then be chosen to provide only the additional needed force to maintain the desired bond strength. A preferred range of useful angles for locking is between 0.03 and 0.07 inches per inch (between about 0.9° to about 2.1°). Tapers at the smaller-taper end of the range tend to grip very tightly, and at the upper end to release easily. It is also within the scope of the invention to design the taper angle and engagement length so that the tapers lock so tightly as to become essentially permanently affixed with a minor amount of force applied by the collar, and, conversely, to release so easily that they must be tightly fastened together using the shape memory collar to transmit significant torque.
In order to maximize the stiffness and minimize the inertia of the assembly, the plug and recess preferably occupy volume inside the bearing that supports the output. It is, however, within the scope of the invention that the unit and it's mating shaft portion be positioned anywhere along the shaft axis.
The inner diameter of the collar may be removed from the shaft by cooling the collar to a temperature that cause the shape memory material to enter the martensite phase, for example, by application of liquid nitrogen to the collar.
The end of the shaft or post is equipped with a concentric hollow recess in the embodiment of
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For example, such limited rotation motors may be used in a laser drilling system for producing vias (or holes) in printed circuit boards (PCBs). The system may include a pair of galvanometer based X-Y scanners as well as an X-Y stage for transporting the PCB, and a scan lens that provides for parallel processing of circuit board regions within the field covered by the scanners and lens. The X-Y stage transports the circuit board along rows and columns needed for entire coverage. The circuit board is typically substantially larger than the scan field.
Such limited rotation motors may also be used in multi-layer drilling systems in accordance with another embodiment of the invention. The operations may include hole punching (or percussion drilling) where one or more laser pulses form a single hole within an effective spot diameter without relative movement of the beam with respect to object, or may include trepanning (which does involve relative movement between the beam and the object during the drilling operation). During trepanning, a hole having a diameter substantially larger than a spot diameter is formed. A substrate is laser drilled from a top surface of the substrate to an exposed bottom surface of the substrate using a plurality of laser pulses that are preferably trepanned in a circle, but other trepanning patterns, such as ovals and squares, may be used. For example, a trepanning pattern of movement of the laser focal spot is one in which the beam spot starts in the center of the desired via, and gradually spirals outwardly to an outer diameter of the via. At that point the beam is caused to orbit around the via center for as many revolutions as is determined necessary for the particular via. Upon completion, the focal spot is caused to spiral back to the center and thereafter awaits the next command. An example of a trepanning velocity is 3 millimeters per second. In such drilling applications, it is sometimes advantageous to provide rapid point to point positioning of the beam with a rapid settling time irrespective of the trajectory between the points.
The overall drilling system throughput can be affected by many factors such as the required number of holes within a field, hole size, stage speed, etc. System bandwidth improvements may be generally useful within a substrate drilling system, and such improvements may be particularly advantageous in substrate drilling systems wherein trepanning or similar motion is used for hole formation. Limited rotation motors discussed above may also be employed for drilling other substrates such as electronic packages, semiconductor substrates, and similar workpieces.
Such limited rotation motors may also be employed in substrate marking employing lasers, or laser marking, of for example, semiconductors, wafers and the like on either front or backsides of the substrates. The marks produced by the laser (such as a diode pumped solid state laser), whether on a front or back side, may be formed as a 1D or 2D matrix, and in compliance with various industry standards. The performance of such a system may depend, at least in part, on marking speed, density, and quality, and improvements in limited rotation motor performance may improve marking speed, density and quality. Marking speed over a field, as measured in mm/sec for example, is a function of the laser repetition rate, spot size, and the speeds of the one or motors (e.g., low and fast scan direction motors) used in the system.
In accordance with further embodiments, systems of the invention may be provided for other high speed marking applications in the electronic industry such as, for example, marking of packages or devices in trays, or other similar workpieces.
Limited rotation motors as discussed above may also be employed in laser trimming systems in accordance with further embodiments of the invention. One or more embodiments of the present invention may be used in a laser trimming system, or in a substrate micromachining system. For example, such a system may provide a method for high-speed, precise micromachining an array of devices (such as resistors), with each of the devices having at least one measurable property (such as resistance). The method includes the steps of: a) selectively micromachining a device in the array to vary a value of a measurable property; b) suspending the step of selectively micromachining; c) while the step of selectively micromachining is suspended, selectively micromachining at least one other device in the array to vary a value of a measurable property; and d) resuming the suspended step of selectively micromachining to vary a measurable property of the device until its value is within a desired range. At least one of the steps of selectively micromachining may include the steps of generating and relatively positioning a laser beam to travel in a first scanning pattern across the devices, superimposing a second scanning pattern with the first scanning pattern and irradiating at least one device with at least one laser pulse.
A micromachining system in accordance with another embodiment of the invention may provide for a fast scan pattern to be carried out using with an acousto-optic deflector, superimposed on a second, lower speed scan pattern that is carried out using a limited rotation motor as discussed above. Generally, the access or retrace time of the acousto-optic deflector is on the order of tens of microseconds. In certain embodiments improved motor speed will directly result in improved trimming speed.
In accordance with further embodiments of the invention, mirrors and other optical elements may be easily and readily mounted to and removed from limited rotation motor shafts using a mirror mounting system of the invention. For example, as shown in
The use of such a collar and removal tool significantly facilitates removal and replacement of optical elements in remote field locations since only the tool, coolant fluid and a replacement collar need to be present at the remote location.
Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the invention.
