Anisotropic damper

Abstract: An anisotropic damper using an elastic member (7) having an E value two times or more larger than that of an elastic member (1) for damping the vibration in the vertical direction to a portion for supporting the rotary part (8) of an optical disk (3) or the like and a mechanical chassis (2) mounting an optical pickup (4) and to the portion for damping the vibration in the planar direction, and comprising two types of elastic members for controlling the fluctuation in the relative distance between the optical pickup and the disk.

Description: The present invention relates to a damper for reducing vibrations through vibration suppression or vibration isolation by using an elastic body for acoustic equipment, video equipment, information equipment, or various types of precision instruments, particularly for an apparatus using an optical disk medium such as a CD, CD-ROM optical disk, or magneto optical disk. A conventional damper for supporting a mechanical chassis of an optical disk unit and so on is a damper comprising one type of elastic body having an E value (dynamic compression elastic modulus) of 9.8x10 0 N/m 2 (1.0x10 4 kg/cm 2 ) or less as shown in Fig. 5 or Fig. 6 of the accompanying drawings, that is a damper is generally used which comprises an elastic body constituted by holding a rotary part 8 of a medium disk 3 and a mechanical chassis 2 mounting an optical transmitter or optical receiver (hereinafter referred to as optical pickup 4) on the face side and fixing them to a box 5 with a screw 6 or the like as shown in Fig. 7. The conventional damper comprising one type of elastic body has a shape shown in Fig. 5 or 6, and the ratio between spring constants in the directions vertical to and parallel with the plane of the disk 3 is between approximately 0.5 and 2 times even if spring constants are changed. Conventionally, the characteristic requested for a damper is to provide an effect of the reduction of transmissibility of vibration acceleration by suppressing vibration so that the relative distance between the disk 3 and the optical pickup 4 can be kept constant, specifically by keeping the natural frequency due to the damper at square root of 0.5 or less to a desired frequency and therefore a spring constant to the total weight of the mechanical chassis 2, disk 3, and optical pickup 4 is obtained. However, the rotating disk 3 produces vibration in the direction vertical to the rotation axis due to weight imbalance caused by dimensional tolerance, machining error or the like, namely in the direction parallel with the disk. Unless the damper has only a low elasticity to the vibration, the mechanical chassis itself greatly vibrates. To stop the vibration, it is necessary to control the vibration with a force larger than the angular moment due to the weight imbalance. To control the vibration, it is preferable to use a method of fixing the mechanical chassis to the box 5. However, if the ratio between spring constants of the damper in the directions vertical to and parallel with the plane of the disk 3 is within a range from approximately 0.5 to 2 times, it is impossible to stop the vibration. On the contrary, vibration having a frequency close to the natural frequency due to the damper, that is resonance, occurs and a worse result occurs. Attention is also drawn to GB-A-452858, disclosing a damper consisting of two materials having different elastic moduli. The damper does not have the shape of a hollow cylinder. The present invention provides an anisotropic damper for supporting a mechanical chassis which is disposed in an apparatus for storing or regenerating data in a non-contact disk information medium such as an optical disk or a magneto optical disk, the apparatus having a rotary motor unit for a medium disk, an optical transmitter or an optical receiver, said damper is a hollow cylinder of which upper and lower parts are increased in diameter and a central part is reduced in diameter so as to serve as a section to be installed to the mechanical chassis or a box chassis; characterized in that: said damper is formed by combining two or more types of elastic bodies having different E values (dynamic compression elastic modulus); a first low-elastic body supporting the mechanical chassis in a direction normal to a face of the disk and damping vibration in the direction normal to the face of the disk; a section installed to the mechanical chassis or a box chassis being wholly or partially formed by a second high-elastic body; the second high-elastic body supporting the mechanical chassis in a direction parallel with the face of the disk, thereby damping vibration in the direction parallel with the face of the disk; whereby the second high-elastic body has an E value two times or more larger than an E value of the first low-elastic body. Therefore, the present invention makes it possible to restrain the fluctuation in the relative distance between an optical unit for writing or reading data in the direction vertical to a disk face and the disk, by forming a part or the whole of a damper for holding a mechanical chassis with a low-elasticity body, and by restraining the self-producing vibration produced due to disk rotation in the disk face direction. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of an anisotropic damper according to the present invention in which the whole of the setting part comprises a high-elasticity body; Figure 2 is a longitudinal sectional view of an anisotropic damper according to the present invention in which a part of the setting part comprises a high-elasticity body; Figure 3 is a sectional view of an anisotropic damper according to the present invention in Fig. 2 in which the support part in the direction vertical to the disk face is decreased in diameter; Figure 4 is a transverse sectional view of the part for setting an anisotropic damper according to the present invention in which a part of the setting part comprises a high-elasticity body and it is radially divided into a plurality of pieces; Figure 5 is a longitudinal sectional view of a conventional damper; Figure 6 is a longitudinal sectional view of a conventional damper in which the support part in the direction vertical to a disk face is decreased in diameter; and Figure 7 is a longitudinal sectional view of a mechanical chassis supported with a damper. The present invention uses a damper for supporting a mechanical chassis without greatly changing the shape of a conventional damper. The present invention is described below in accordance with the embodiments shown in Figs. 1 and 2. The elastic body used for the part for supporting it in the direction vertical to the plane of disk 3 (see Fig. 7) is a rubber-like elastic body having an E value of 9.8x10 0 N/m 2 (1.0x10 4 kg/cm 2 ) or less (hereinafter referred to as low-elasticity body 1). The E value of 9.8x10 0 N/m 2 (1.0x10 4 kg/cm 2 ) or less corresponds to 70 hardness or less in terms of the JIS (Japan Industrial Standards) rubber hardness class A . Therefore, the rubber-like elastic body has a general rubber elasticity. Moreover, the elastic body used for the mechanical chassis serving as a part for supporting it in the direction parallel with the disk, or for the whole 7a or a part 7b of the cylindrical portion installed to the box chassis is an elastic body (hereinafter referred to as high-elasticity body 7) having an E value two times or more larger than the E value of the low-elasticity body. A damper of the present invention is characterized by combining and integrating the low-elasticity body 1 and the high-elasticity body 7 having different E values from each other, and thus by suppressing by a low-elasticity body the vibration from the outside to the inside of a mechanism causing fluctuation in the relative distances between an optical pickup 4 and the disk 3 when writing or reading data in the direction vertical to the plane of the disk 3 and the vibration due to the natural vibration of the disk face from the inside to the outside of the mechanism in the direction vertical to the disk plane, and by damping by means of the high-elasticity body 7 the self-producing vibration caused by disk rotation in the disk face direction. A material having a loss factor of tan δ =0.01 or more and a high internal damping property is effective as a high-elasticity body used for this. Another embodiment as shown in Fig. 3 is characterized by forming a low-elasticity body into a hollow cylinder in which upper and lower parts 1a and 1b are increased in diameter and a central part 1c is decreased in diameter so that the low-elasticity body is inserted into and engaged with a hole formed in the mechanical chassis 2 of an optical disk unit, by improving the vibration isolation characteristics in the vertical direction by decreasing the spring constant in the direction vertical to the disk face, by disposing the high-elasticity body 7b to the axis side of the central small-diameter part 1c, and thereby by forming a composite elastic body with improved vibration isolating characteristics in the direction parallel with the disk face. The damper shown in Fig. 4 is characterized by dividing a high-elasticity body used for the whole or a part of the side central small-diameter part 1c serving as a portion installed to a mechanical chassis for supporting it in the direction parallel with the plane of the disk 3 or a box chassis into a plurality of pieces, and by radially disposing them in the low-elasticity body 1 so that crushing in the direction vertical to an axis can be easily performed and each chassis can be easily engaged with a installing hole. A composite damper of the present invention is manufactured by a method of forming a low-elasticity body and a high-elasticity body with a thermosetting or thermoplastic member by a metal mold which is a well known art and then of bonding the low-elasticity body and high-elasticity body, a method of forming either a low-elasticity body or high-elasticity body by a metal mold and then of inserting it into the remaining elastic body forming mold, or an insert-forming or double injection molding method of forming a low-elasticity body and a high-elasticity body with a thermoplastic member in accordance with injection forming. A damper is manufactured by increasing the upper and lower parts 1a and 1b of an elastic body in diameter and decreasing the central part 1c of the elastic body in diameter, using the high-elasticity body 7b having an E value two times or more larger than the E value of the upper and lower parts of the elastic body for the inside of the central part 1c, by forming the high-elasticity body 7b into a ring shape by means of injection molding, by inserting the annular high-elasticity body into a low-elasticity body forming metal mold, and then by injection-molding the upper and lower parts 1a and 1b of the low-elasticity body. As the elastic body material, styrene-based thermoplastic elastomer JIS A with Hs of 40 hardness and E value of 50 kg/cm 2 is used for the low-elasticity body material of the large-diameter parts 1a and 1b. As other low-elasticity body materials, the following are given: natural rubber, chloroprene rubber, butyl rubber, silicone rubber, urethane rubber and thermoplastic elastomer (styrene, olefin, polyester, or urethane based). Elastomer with an E value of 9.8x10 0 N/m 2 (1.0x10 4 kg/cm 2 ) or less is preferably used. As the material of the high-elasticity body of the small-diameter part 7b, polypropylene (PP) with E of 1.96x10 1 N/m 2 (2.0x10 4 kg/cm 2 ) is used and dampers were manufactured from three types of elastic bodies tan δ =0.005, tan δ =0.01, and tan δ =0.05. As other high-elasticity body materials, the following resins are given: the above elastomer, and polyethylene (PE), polyvinylchloride (PVC), polystyrene (PS), acrylonitrile, butadiene, styrene resin (ABS), polyamide (PA), polyacetal (POM), polycarbonate (PBT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), epoxy resin (EP), silicone resin (SI), and polyurethane (PUR). Vibration tests were performed using the embodiments 1 to 4 of the present invention which are composite elastic bodies manufactured as described above and comparative example 1 (conventional product) entirely made of the same elastic body. The material of the comparative example 1 is butyl rubber and has the shape shown in Fig. 5 which is the same as that in Fig. 2. The vibration test was performed by supporting a 150g mechanical chassis at four points with dampers, by exciting the chassis with the frequency of 100 Hz at which a disk resonates, and by measuring the acceleration on the mechanical chassis to the excitation acceleration of the vibration. Thus, the acceleration on the mechanical chassis to the excitation acceleration was obtained as a ratio (%). The results obtained are shown in Table 1 below. By the measurement results in Table 1, it is found that the comparative example 1 and the embodiments 1, 2, and 3 have the same transmissibility of vibration in the direction vertical to the disk. However, in the case of the embodiment 4 having the shape shown in Fig. 3, the low-elasticity body was radially divided and arranged. Therefore, the natural frequency was lowered and thereby the transmissibility of vibration was also lowered, and the vibration isolating effect was improved. As the measuring result of the acceleration ( G value) according to a mechanical deflection test in the direction parallel with a disk, mechanical deflection occurred because the spring constant in the direction parallel with the disk was small, so a large G value resulted. In the case of the embodiment 1, as the spring constant was large, mechanical deflection was suppressed and the G value could be reduced to approximately 1/3 of the G value of a conventional damper. In the case of the embodiments 2, 3, and 4, the G value could be further reduced because a material having a large loss factor was used for the high-elasticity body. Moreover, the G values in the direction parallel with a disk were measured when the ratio between E values of the high-elasticity body and low-elasticity body is 2, 20, and 200 times in the case of the shape shown in Fig. 2. A sample having the same shape and the ratio between E values of high- and low-elasticity bodies which is 1.5 times was used for the comparative example 2. The results obtained are shown in Table 2 below. In Table 2, it is impossible to accurately read data from a disk because the comparative example 2 has a large G value equal to that of the comparative example 1 entirely made of the same elastic body and the mechanical deflection is large. In the case of the embodiment 5 in which the E value of the high-elasticity body is two times that the low-elasticity body, the G value due to mechanical deflection was halved compared to the case of the comparative example 2 and no erroneous operation was observed. Moreover, when the E value is 20 times that of embodiment 6 and 30 times that of embodiment 7, the G value was reduced and preferable results were obtained. From the above results, it is found that mechanical deflection can be reduced by setting the E value of the high-elasticity body to a value two times or more larger than that of the low-elasticity body and automatic vibration of a high-double-speed mechanics can be controlled. Embodiments of the present invention are described above. However, these embodiments are just examples. The present invention allows other various shapes corresponding to the shapes (boss, pin, or setting) of the counterparts. A damper according to the present invention makes it possible to realise the same vibration isolating effect in the direction vertical to a disk face as that of a conventional damper and suppress the vibration in the disk face direction by a combined structure with the high-elasticity body 7. A low-elasticity body provides a preferable effect by decreasing the E value of a rubber-like elastic body to 9.8x10 0 N/m 2 (1.0x10 4 kg/cm 2 ) or less in order to decrease the natural frequency of the damper. In the case of a high-elasticity body, a force for suppressing vibration, that is the vibration suppression effect, is obtained without resonating with the vibration in the disk face direction by setting the E value of the high-elasticity body to a value two times or more larger than that of the low-elasticity body. For example, when the spring constant ratio according to a shape is increased up to two times and the E value is increased up to two times, the total spring constant ratio is increased up to four times. Therefore, the natural frequency can be obtained by square root, and thus it is increased up to two times. Thereby, it is possible to lower the natural frequency in the direction vertical to the disk face and to raise the natural frequency in the direction of the disk face at both sides of a desired frequency. Moreover, by setting tan δ of the high-elasticity body to 0.01 or more, it is possible to damp the self-producing vibration inside of the high-elasticity body and to further improve the vibration suppressing effect. Furthermore, by forming a low-elasticity body into a hollow cylinder, it is possible to easily decrease the spring constant and improve the vibration suppression characteristics in the direction vertical to a disk face, without reducing the vibration suppressing effect in the disk face direction by the high-elasticity body. Therefore, a damper according to the present invention is most suitable for vibration suppression and vibration isolation of acoustic equipment, video equipment, information equipment, or various types of precision instruments, particularly an apparatus using an optical disk medium such as a CD, CD-ROM optical disk, or magneto optical disk. Moreover, when mounting a damper according to the present invention on a unit, a high-elasticity body is divided into a plurality of pieces to be disposed in the radial direction. The high-elasticity body can be easily mounted because a spring crushed in the direction vertical to the damper axis is deformed as a low-elasticity body, and only a small force is required compared to a high-elasticity body which is not divided. Furthermore, it is possible to insert-form a damper of the present invention by means of a general injection molding machine or to double-injection molding the damper with a plurality of metal molds by using a thermoplastic member as a material of a low-elasticity body and high-elasticity body, to realise an automated and labour saving process, and thus to decrease the manufacturing process cost.

Claims: An anisotropic damper for supporting a mechanical chassis (2) which is disposed in an apparatus for storing or regenerating data in a non-contact disk information medium such as an optical disk or a magneto optical disk, the apparatus having a rotary motor unit (8) for a medium disk (3), an optical transmitter or an optical receiver (4), said damper being a hollow cylinder of which upper and lower parts are increased in diameter and a central part is reduced in diameter so as to serve as a section to be installed to the mechanical chassis (2) or a box chassis; characterized in that : said damper is formed by combining two or more types of elastic bodies (1,7) having different E values; a first low-elastic body (1) supporting the mechanical chassis (2) in a direction normal to a face of the disk (3) and damping vibration in the direction normal to the face of the disk (3); a section installed to the mechanical chassis (2) or a box chassis being wholly or partially formed by a second high-elastic body (7); the second high-elastic body (7) supporting the mechanical chassis (2) in a direction parallel with the face of the disk (3), thereby damping vibration in the direction parallel with the face of the disk (3); whereby the second high-elastic body (7) has an E value two times or more larger than an E value of the first low-elastic body (1), wherein the E-value is the dynamic compression elastic modulus. An anisotropic damper as claimed in claim 1, characterized in that the low-elasticity body (1) has an E value 9.8x10 0 N/m 2 or less and a loss factor of 0.01 or more. An anisotropic damper as claimed in claim 1 or 2, characterized in that the high-elastic body (7) is formed as one cylinder. An anisotropic damper as claimed in any of claims 1 to 3, characterized in that the low-elastic body (1) and the high-elastic body (7) are made of a thermosetting member or a thermoplastic member and integrated into one piece by one of a bonding method, an insert-molding method or a double injection molding method. An anisotropic damper as claimed in any of claims 1 to 4, characterized in that the low-elastic body (1) has a hardness of 70 or less in terms of the JIS rubber hardness class A.

Inventors: ITAKURA MASAYUKI, KIDOKORO YUKIHIRO, ITAKURA, MASAYUKI, KIDOKORO, YUKIHIRO, Itakura, Masayuki, c/o Polymatech Co., Ltd., Kidokoro, Yukihiro, c/o Polymatech Co., Ltd.
Applicants: POLYMATECH CO LTD, POLYMATECH CO., LTD.
Application year: 1997
Main classification: G11B33
IPC codes: F16F15, G11B19, F16F3, F16F1, G11B33