Patent Application
20090062024
This invention is generally related to mounting structures, and more particularly to mounting structures for lightweight, limited rotation mechanical parts.
Limited rotation mechanical parts are used in many products. For example, limited rotation oscillatory motors (galvanometers) are used to rotate mirrors in discreet steps to direct light beams in optical scanners. High frequency limited rotation exerts considerable torque on the rotating parts during acceleration and deceleration. Consequently, the rate of rotation is limited by the first torsional resonance frequency of the rotating assembly, which is at least in-part a function of shape and mass. Shape is often constrained by the function of the part, e.g., the required dimensions of the mirror. However, various techniques are known for reducing mass, and thereby increasing the first torsional resonance frequency. For example, a prior art optical scanner as illustrated in
One technically difficult aspect of manufacturing a mirror and coupling assembly is bonding the mirror (101) to a shaft coupling (105) with adequate strength. In order to couple the mirror to a motor, the base of the mirror is first bonded into a transverse slot (101C) in the shaft coupling (105). The shaft coupling is then mounted on the motor shaft. Alternatively, the motor shaft itself includes a transverse slot adapted to receive the mirror.
The transverse slot (101C) is defined by flanges (107A, 107B). Since flange (107B) necessarily protrudes beyond the plane of the reflective surface (101B) of the mirror (101), it is not practical to finalize the polishing of the reflective surface subsequent to mounting the mirror into the transverse slot. For that reason, it is common practice to finish polishing the reflective surface before mounting. This is problematic because any stresses induced by the mounting and bonding process can distort the reflective surface of the mirror. For example, bonding temperatures may be limited to about 160° C. in order to avoid stressing the mirror. While the depth (106) of the mating surface might be increased to enhance bonding, that would undesirably increase the length of the portion of the finished assembly which is cantilevered from the motor. An improved mirror mounting technique would therefore be desirable.
In accordance with one embodiment of the invention, apparatus for mounting a mirror to a limited rotation motor comprises: a disk segment having an edge adapted to be aligned with a plane defined by a reflective surface of the mirror, the disk segment having a mating surface against which a prepared base surface of the mirror is secured, the disk segment being adapted to be coupled to the motor.
In accordance with another embodiment of the invention, a method for mounting a mirror to a limited rotation motor comprises: securing a disk segment to the mirror, the disk segment having an edge adapted to be aligned with a plane defined by a reflective surface of the mirror, and a mating surface against which a prepared base surface of the mirror is secured, the disk segment being adapted to be coupled to the motor.
One of the advantages of the invention is that the mirror can be finished after the mirror has been attached to the disk segment. Prior art mounting systems protrude beyond the plane defined by the reflective surface of the mirror. Such protrusion impedes access to the reflective surface. Consequently, prior art systems mount finished mirrors, which are susceptible to heat and stress caused by the mounting technique. Since the disk segment does not protrude beyond the plane define by the reflective surface of the mirror, the mirror may be processed for stress-relief and the reflective surface may be polished subsequent to mounting on the disk segment. This is particularly advantageous because attaching the mirror to the disk segment before the mirror is finished enables use of attachment techniques that require relatively high heat and other conditions that would be damaging to a finished mirror.
Another one of the advantages of the invention is that the length of the overall mirror assembly may be reduced. At least some prior art mounting systems utilize a transverse slot which receives the base of the mirror. The strength of the joint formed in the transverse slot is at least in-part a function of slot depth. However, increasing slot depth tends to increase the length of the overall assembly for a mirror of given length. This is problematic because the assembly is cantilevered from the motor, and increasing the length therefore increases susceptibility to vibration. At least one embodiment of the present invention mitigates this problem by securing the mirror to the disk segment on a planar prepared base surface, i.e., without flanges. Use of such a joint is enable because the mirror is mounted prior to finishing, such as by soldering or brazing, which are relatively strong but would possibly damage a finished mirror.
Referring to
After the mirror has been attached to the alignment pin and disk segment, the mirror can be finished. For example, the mirror may be processed for stress-relief, and the reflective surface may be polished. Polishing of the reflective surface (301B) is facilitated by the alignment of the flat edge (206) of the disk segment with the plane defined by the reflective surface of the mirror. In particular, the disk segment (203) does not impede access to the reflective surface by polishing equipment because the disk segment does not protrude beyond the plane defined by the reflective surface. This is particularly advantageous because attaching the mirror to the disk segment before the mirror is finished enables use of attachment techniques that require relatively high heat and other conditions that would be damaging to a finished mirror.
After the mirror has been finished, the mirror/disk segment sub-assembly is mounted on the shaft coupling (205). The shaft coupling includes a half-blind hole positioned to receive the stub of the alignment pin which protrudes from the disk segment. The half-blind hole of the shaft coupling may, but need not necessarily, be formed along the axis of rotation of the shaft coupling. Once the mirror/disk segment sub-assembly is aligned with the shaft coupling by the pin, the sub-assembly is secured to the shaft coupling.
Any of various means known in the art may be utilized to secure the sub-assembly to the shaft coupling. In the illustrated embodiment, a threaded clamp ring is utilized. In particular, the threaded clamp ring is mated to corresponding threads on outer, arcuate surfaces of the disk segment and shaft coupling. It will be appreciated that in order to avoid cross-threading, the threads of the disk segment must be aligned with the threads of the shaft coupling. Consequently, the rotational alignment of the disk segment relative to the shaft coupling is defined by the threads of the disk segment and the shaft coupling.
Referring now to
The shaft coupling (205) is adapted to be mounted to the motor with a rotational position selectable at the time of mounting, i.e., the mirror can be oriented relative to the motor in any of various positions. In the illustrated embodiment, the shaft coupling (205) defines a male taper which corresponds to a female taper defined by the motor shaft, thereby permitting a press-fit in a selected orientation. This feature advantageously permits rotational alignment in situ, which may facilitate mirror replacement in addition to simplifying manufacture.
Various materials may be utilized to form the parts of the mirror mount. Because of the advantages associated with low mass, low density materials may be preferable. Since limited rotation mirrors are commonly manufactured from Beryllium, at least at the present time, the alignment pin, clamp ring, disk segment, and shaft coupling should presently be manufactured from compatible materials, i.e., materials of sufficiently high Young's Modulus which have a coefficient of thermal expansion that is similar to that of the mirror material. Titanium, stainless steel and Beryllium are examples of some materials from which the parts may be manufactured. It should also be noted that although the various parts are illustrated as being separate, some parts could be formed as a single integral part. For example, combinations of two or more of the mirror, alignment pin and disk segment could be cast or machined from a single block of material. Silver-copper and silver-tin-copper alloys are examples of soldering and brazing materials which may be utilized.
While the invention is described through the above exemplary embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while the preferred embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the invention should not be viewed as limited except by the scope and spirit of the appended claims.
