PIEZOELECTRIC VIBRATION GENERATOR AND VIBRATORY PARTS FEEDER INCORPORATING THE SAME

Abstract: A piezoelectric vibration generator (3) interconnecing a base (1) and a vibratory conveyor table (2) of a piezoelectrically driven vibratory parts feeder includes a pair of resilient plate members (5, 10) joined together at their lower ends and disposed in a configuration substantially folded about the joint therebetween. The vibration generator of the folded configuration has a relatively small length and hence is capable of reducing the overall height of the vibratory parts feeder. A further advantage attained by the folded vibration generator (3) is that the amplitude of vibrations is not limited depending upon the distance between the base (1) and the vibratory conveyor table (2).

Description: The present invention relates to a piezoelectric vibration generator having piezoelectric elements attached to opposite surfaces or sides of a resilient plate for generating slight vibratory motion, and also to a vibratory parts feeder incorporating such piezoelectric vibration generator for feeding small parts or articles in a predetermined supplying direction. Typical piezoelectrically driven vibratory parts feeders of the type described are disclosed in Japanese Patent Laid-open publication (JP-A) No. 62-4118, 62-4119 and 62-4120. The disclosed parts feeders include a base and a vibratory conveyor table supported on the base by means of a plurality of properly spaced apart and obliquely disposed piezoelectric vibration generators. Each of the piezoelectric vibration generators comprises a leaf spring secured at a lower end to the base and carrying on its opposite surfaces a pair of piezoelectric elements, and an elongate resonant or amplitude enhancing member extending continuously and upwardly from the upper end of the leaf spring and secured at its upper end to the vibratory conveyor table. The amplitude enhancing member has a stiffness smaller than the stiffness of the leaf spring and hence is bendable easier than the leaf spring. When the piezoelectric elements are driven by an alternating voltage, the leaf spring is caused to shorten and lengthen alternately, thus producing longitudinal vibrations whose amplitude is in turn enhanced by the amplitude enhancing member. The thus enhanced vibratory impulses are imparted to the vibratory conveyor table, causing small parts or articles to move in a predetermined supplying direction along a path defined on the upper surface of the covnveyor table. The amplitude enhancing member is formed either as a separate connecting member which is structurally independent of the leaf spring, or as an upper extension of the leaf spring which is integral with the leaf spring. With the provision of the amplitude enhancing member, relatively large vibratory impulses can be imparted to the vibratory conveyor table. However, the amplitude of vibrations thus obtained is still limited to a certain level as the overall length of the vibration generator is determined depending upon the distance between the base and the vibratory conveyor table. It is therefore likely to occur that a desired amplitude of vibration cannot be produced from the prior art vibration generator. Another difficulty associated with the prior art vibratory parts feeder is that the amplitude enhancing member, which extends upwardly from the upper end of the leaf spring and has a smaller stiffness than the leaf spring, must be rigid enough to withstand the loads imparted thereon from the vibratory conveyor table. Since the stiffness of the amplitude enhancing member is inversely proportionate to the amplitude of vibrations produced from the vibration generator, setting of the amplitude of vibrations requires a fine adjustment of the stiffness of the amplitude enhancing member, which is tedious and time-consuming. Furthermore, the prior art vibratory parts feeder is relatively large in height as the leaf spring and the amplitude enhancing member extend linearly between the base and the vibratory conveyor table. JP-A-62-4119, on which the preamble of claim 1 is based, discloses a piezoelectric vibration generator comprising: - at least a pair of resilient plate members, said pair or each said pair of resilient plate members comprising a first resilient plate member and a second resilient plate member joined together at their one ends; and first and second piezoelectric elements attached, respectively, to a front surface and a rear surface of one of said resilient plate members. JP-A-62-4119 also discloses a piezoelectrically driven vibratory parts feeder, on which the preamble of claim 10 is based. The piezoelectrically driven vibratory parts feeder incorporates one or more piezoelectric vibration generators. However, in the piezoelectric vibration generator of JP-A-62-4119 the first and second resilient members are arranged linearly, one after another. Therefore, the piezoelectrically driven vibratory parts feeder of JP-A-4119 has a large height. Furthermore, it is difficult to adjust the amplitude of the vibrations of the piezoelectric vibration generator of JP-A-62-4119. With the foregoing difficulties in view, the present invention seeks to provide a piezoelectric vibration generator for a vibratory parts feeder, which is capable of producing a desired amplitude of vibrations irrespective of the distance between a base and a vibratory conveyor table of the parts feeder. The present invention further seeks to provide a piezoelectric vibration generator which is rigid enough to withstand the loads imparted thereon from the vibratory conveyor table of a vibratory parts feeder incorporating the vibration generator. The present invention further seeks to provide a piezoelectric vibration generator for a vibratory parts feeder, which is small in height and hence is capable of reducing the overall height of the vibratory parts feeder. The present invention further seeks to provide a piezoelectric vibration generator for producing slight vibrations whose amplitude can be adjusted easily without the necessity of a fine adjustment of the stiffness of the vibration generator. The present invention further seeks to provide a piezoelectrically driven vibratory parts feeder which is relatively low in height and can easily be incorporated in a processing machine. According to a first aspect of the present invention there is provided a piezoelectric vibration generator comprising: - at least a pair of resilient plate members, said pair or each said pair of resilient plate members comprising a first resilient plate member and a second resilient plate member joined together at their one ends; and first and second piezoelectric elements attached, respectively, to a front surface and a rear surface of one of said resilient plate members; said piezoelectric generator being characterised in that said pair or each said pair of resilient plate members is/are disposed in a configuration substantially folded about the joint between the first resilient plate member and the second resilient plate member; and in that at least one of said resilient plate members is adjustable in length. According to a second aspect of the present invention there is provided a piezoelectrically driven vibratory parts feeder comprising: - a stationary base; a vibratory conveyor table; and at least one piezoelectric vibration generator comprising: - at least a pair of resilient plate members, said pair or each said pair of resilient plate members comprising a first resilient plate member and a second resilient plate member joined together at their one ends; and first and second piezoelectric elements attached, respectively, to a front surface and a rear surface of one of said resilient plate members; wherein said at least one piezoelectric vibration generator interconnects said base and said vibratory conveyor table and is operable to impart vibratory impulses to said vibratory conveyor table, and wherein an other end of said first resilient plate member is connected to said base, and an other end of said second resilient plate member is connected to said vibratory conveyor table; said piezoelectrically driven vibratory parts feeder being characterised in that said pair or each said pair of resilient plate members is/are disposed in a configuration substantially folded about the joint between the first resilient plate member and the second resilient plate member; and in that at least one of said resilient plate members is adjustable in length. Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example. Figure 1 is a front elevational view, with parts cut away for clarity, of a vibratory parts feeder incorporating piezoelectric vibration generators according to the present invention; Figure 2 is a plan view, with parts cut away for clarity, of the vibratory parts feeder shown in Figure 1; Figure 3 is an enlarged exploded perspective view of one of the piezoelectric vibration generators shown in Figure 9; Figure 4 is a perspective view showing a modified resonant member of the piezoelectric vibration generator; Figure 5 is a view similar to Figure 12, but showing another modification of the resonant member; Figure 6 is a plan view, with parts cut away for clarity, of a modified vibratory parts feeder; Figure 7 is a front elevational view of the vibratory parts feeder shown in Figure 6; and Figures 8A through 8C are enlarged front elevational views respectively showing different brackets used for the attachment of the piezoelectric vibration generator to a base of the vibratory parts feeder shown in Figure 6. Figures 1 and 2 show a piezoelectrically driven vibratory parts feeder incorporating piezoelectric vibration generators according to the present invention. The illustrated parts feeder is of the vibratory feeder bowl type but the present invention is also applicable to a vibratory parts feeder of the linear vibratory feeder type. Figures 1 and 2 show a vibratory parts feeder according to the present invention. The parts feeder includes a horizontal base 17 firmly connected to the upper end of a vertical supporting post 18, a circular vibratory conveyor table 19 disposed above the base 17 and carrying thereon a parts feeder bowl 20, and a plurality (four in the illustrated embodiment) of piezoelectric vibration generators 3f interconnecting the base 17 and the vibratory conveyor table 19. The base 17, as shown in Figure 2, is in the shape of a windmill having four identical rectangular wings 17a. Each of the piezoelectric vibration generators 3f includes a vertically disposed first resilient plate member 5f firmly connected at its upper end to one of two adjacent sides of each respective rectangular wing 17a, and an obliquely disposed second resilient plate member 10f connected at its lower end to the lower end of the first resilient plate member 5f via a rectangular connector block 21, the upper end of the second resilient plate member 10f being firmly secured to the peripheral surface of the circular vibratory conveyor table 18. The first resilient plate member 5f carries on its opposite surfaces or sides a pair of piezoelectric elements 7, 8. In operation, an alternating voltage is applied to the piezoelectric elements 7, 8 to shorten and lengthen the piezoelectric elements 7, 8 and, consequently, the first resilient plate member 5f, thereby producing slight longitudinal vibrations on the first resilient plate member 5f. The thus produced longitudinal vibrations are amplified or enhanced by the second resilient plate member 10f and then imparted to the vibratory conveyor table 19, thereby causing small parts or articles to move upwardly along a helical spiral feed path or track provided in the non-illustrated vibratory feeder bowl. The amplitude of vibrations to be imparted to the vibratory conveyor table 19 can be adjusted accurately and easily by changing the length and/or the thickness of the second resilient plate member 10f. The second resilient plate member 10f may be notched when a fine adjustment of the amplitude of vibrations is necessary. Since the vibration generator 3f has a folded configuration, the overall length or longitudinal extent of the vibration generator 3f is relatively small. Consequently, a substantial reduction of the overall height of the vibratory parts feeder can be attained. Furthermore, loads acting on the second resilient plate member 10f are efficiently absorbed by such folded configuration of the vibration generator 3f and hence the vibration generator 3f is subjected to only a small bending moment. The vibration generator 3f is therefore durable in construction. As shown in Figure 3, attachment of the upper end of the first resilient plate member 5f to the base 17 is performed by means of a pair of screws 22 which pass successively through spring washers 23, washers 24, holes in a presser plate 25, and holes in the plate member 5f and are threaded into threaded holes in the base 17. Likewise, the lower end of the plate member 5f is connected to the connector block 21 by a pair of screws 26 that pass successively through spring washers 23, washers 24, holes in another presser plate 25, holes in the plate member 5f, and transverse holes in the connector block 21 and are threaded into threaded holes in a retainer plate 27. The retainer plate 27 may be omitted when the transverse holes in the connector block 21 are internally threaded. The connector block 21 further has a threaded longitudinal hole 28 into which a screw 29 is threaded to attached the lower end of the second resilient plate member 10f to the connector block 21. The screw 29 passes successively through a spring washer 23, a washer 24, a hole in the presser plate 30, and a lower hole in the second resilient plate member 10f. The upper end of the second resilient plate member 10f is secured by a screw 29 that passes through a spring washer 23, a washer 24, a hole in another presser plate 30, and an upper hole in the plate member 10f. Each of the first and second resilient plate members 5f, 10f is formed of a flat rectangular resilient plate of metal or synthetic resin. The second resilient plate member 10f lies in a vertical plane extending tangentially with respect to the peripheral surface of the circular vibratory conveyor table 19. The first resilient plate member 5f lies in a plane extending at an angle α of about 90 degrees, as shown in Figure 2. This angle α can be varied by displacing the first resilient plate member 5f along the side of the rectangular wing 17a. When the first resilient plate member 5f is displaced inwardly of the base 17, the angle α becomes greater than 90 degrees. Conversely, the angle α becomes smaller than 90 degrees as the plate member 5f is displaced outwardly of the base 17. The adjustment of the angle α is performed in such a manner as to enable the second resilient plate member 10f to be attached to the peripheral surface of the circular vibratory conveyor table 19. As shown in Figure 1, the second resilient plate member 10f is inclined with respect to the vertical (indicated by the phantom line L) at an angle of ϑ. This angle ϑ is nearly equal to the angle of inclination of a helical spiral feed path or track provided in the parts feeder bowl 20 but, in practice, it is experimentally determined with reference to the angle of inclination of the helical spiral feed path. The angle ϑ can be varied either by changing the length of the second resilient plate member 10f, by displacing the position of the joint between the first and second resilient plate members 5f, 10f inwardly or outwardly of the base 17, or by displacing the first resilient plate member 5f inwardly or outwardly of the base 17. The change of the length of the second resilient plate member 10f can be achieved simply by replacing the plate member 10f with another plate member whose length is different to the length of the plate member 10f. Alternatively, it is possible to use a second resilient plate member which is adjustable in length, such as shown in Figures 4 and 5. The plate member 10f' shown in Figure 4 includes a channel shaped elongate holder 31 adapted to be connected at its one end to the vibratory conveyor table 19 (Figure 1 ), and an elongate slide 32 slidably received in a longitudinal guide channel in the holder 31 and having a longitudinal groove 33. A lock screw 34 passes through a longitudinal slot in the holder 31 and through the longitudinal groove 33 in the slide 32 and is threaded into a threaded hole (not shown) formed in the bottom wall of the holder 31. When the screw 34 is loosened, the slide 32 is movable along the guide channel in the holder 31 to thereby change the overall length of the plate member 10f'. The slide 32 is locked in position against displacement by tightening the screw 34 until the slotted upper wall of the holder 31 is resiliently flexed inwardly toward the bottom wall, thus gripping the slide 32 by and between the upper and bottom walls of the holder 31. A modified second resilient plate member 10f'' shown in Figure 5 includes a pair of flat rectangular plate elements 35, 35 interconnected at their one ends by a stud screw 36. The overall length of the plate member 10f'' can be varied by turning at least one plate element 35 in either direction. Figures 6 and 7 show the manner in which the position of the joint between the first and second resilient plate members 5f, 10f is displaced inwardly and outwardly with respect to the vertical support post 18 for adjustably changing the angle of inclination of the second resilient plate member 10f. In the illustrated embodiment, the adjustment of this inclination angle is achieved by utilizing a mounting bracket 37 which is detachably connected by screws 38 to the base 17 and to which the upper end of the first resilient plate member 5f is firmly secured. The mounting bracket 37 has a length L1 as shown in Figure 8A. When the angle of inclination of the plate member 10f is to be changed, the mounting bracket 37 is replaced by another mounting bracket 39 which has a smaller length L2 than the mounting bracket 37, as shown in Figure 8B. As an alternative, the mounting bracket 37 may be replaced with a mounting bracket 40 having a sloped surface 41 on which one side of the first resilient plate member 5f is disposed flatwise when the plate member 5f is connected at its upper end to the base 17. The vibratory parts feeders shown in Figures 1 to 7 are advantageous over the prior art vibratory parts feeders in that when an adjustment of the amplitude and direction of vibrations is necessary, the angle of inclination of the second resilient plate member 10f can be easily adjusted to a desired value either by replacing the second resilient plate member 10f with another one having a different length, or by changing the length of the second resilient plate member 10f', 10f'', without the necessity of replacement of the first resilient plate member on which the piezoelectric elements 7, 8 are attached. Furthermore, such adjustment can be carried out easily because the second resilient plate member 10f is attached to the peripheral surface of the vibratory conveyor table 19 and hence is easily accessible.

Claims: A piezoelectric vibration generator (3f) comprising:- at least a pair of resilient plate members (5f, 10f ), said pair or each said pair of resilient plate members (5f, 10f) comprising a first resilient plate member (5f) and a second resilient plate member (10f) joined together at their one ends; and first and second piezoelectric elements (7, 8) attached, respectively, to a front surface and a rear surface of one of said resilient plate members (5f, 10f); said piezoelectric generator being characterised in that said pair or each said pair of resilient plate members (5f, 10f) is/are disposed in a configuration substantially folded about the joint between the first resilient plate member (5f) and the second resilient plate member (10f); and in that at least one of said resilient plate members (5f, 10f) is adjustable in length. A piezoelectric vibration generator (3f) according to claim 1, wherein said pair or each said pair of resilient plate members (5f, 10f) is disposed with a longitudinal axis of said first resilient plate member (5f) at an angle to a longitudinal axis of said second resilient plate member (10f). A piezoelectric vibration generator (3f) according to claim 1 or 2, said first resilient plate member (5f) of said pair or of each said pair of resilient plate members having one face lying in a plane extending at an angle to a face of the second resilient plate member (10f). A piezoelectric vibration generator (3f) according to claim 3, said angle being equal or nearly equal to 90 degrees. A piezoelectric vibration generator (3f) according to any preceding claim, said first and second resilient plate members of said pair or of each said pair of resilient plate members (5f, 10f) having the same thickness. A piezoelectric vibration generator (3f) according to any preceding claim, said first and second resilient plate members (5f, 10f) of said pair or of each said pair of resilient plate members having different lengths. A piezoelectric vibration generator (3f) according to claim 6, the second resilient plate member (10f) being longer than said first resilient plate member (5f). A piezoelectric vibration generator (3f) according to any preceding claim, said second resilient plate member (10f') of said pair or each said pair of resilient plate members including an elongate holder (31), a slide (32) movably received in said holder (31), and a fastener (34) for locking the slide (32) in position against displacement relative to said holder (31). A piezoelectric vibration generator (3f) according to any of claims 1 to 7, said second resilient plate member (10f'') of said pair or each said pair of resilient plate members including a pair of elongate plate elements (35, 35), and a stud screw (36) interconnecting one ends of said plate elements (35). A piezoelectrically driven vibratory parts feeder comprising:- a stationary base (17); a vibratory conveyor table (19); and at least one piezoelectric vibration generator (3f) comprising : - at least a pair of resilient plate members (5f, 10f), said pair or each said pair of resilient plate members (5f, 10f) comprising a first resilient plate member (5f) and a second resilient plate member (10f) joined together at their one ends; and first and second piezoelectric elements (7, 8) attached, respectively, to a front surface and a rear surface of one of said resilient plate members (5f, 10f); wherein said at least one piezoelectric vibration generator (3f) interconnects said base (17) and said vibratory conveyor table (19) and is operable to impart vibratory impulses to said vibratory conveyor table (19), and wherein an other end of said first resilient plate member (5f) is connected to said base (17), and an other end of said second resilient plate member (10f) is connected to said vibratory conveyor table (19); said piezoelectrically driven vibratory parts feeder being characterised in that said pair or each said pair of resilient plate members (5f, 10f) is/are disposed in a configuration substantially folded about the joint between the first resilient plate member (5f) and the second resilient plate member (10f); and in that at least one of said resilient plate members (5f, 10f) is adjustable in length. A piezoelectrically driven vibratory parts feeder according to claim 10, said vibratory conveyor table (19) being disposed above said base (17), the other ends of said first and second resilient plate members (5f, 10f) being secured, respectively, to an outer side surface of said base (17) and an outer side surface of said vibratory conveyor table (19). A piezoelectrically driven vibratory parts feeder according to claim 10 or 11, said first resilient plate member (5f) of said pair or each said pair of resilient plate members having a longitudinal axis extending substantially vertically and having one face lying in a first vertical plane, said second resilient plate member (10f) of said pair or each said pair of resilient plate members having a longitudinal axis extending at a first angle to the vertical and having one face lying in a second vertical plane extending at a second angle to said first vertical plane. A piezoelectrically drive vibratory parts feeder according to claim 12, said second angle being equal or nearly equal to 90 degrees. A piezoelectrically drive vibratory parts feeder according to claim 12 or 13, further including changing means for changing said first angle, said changing means comprising a mounting bracket (37; 39; 40) secured to said outer side surface of said base (17) and supporting thereon said other end of said first resilient plate member (5f) of said pair or each said pair of resilient plate members. A piezoelectrically driven vibratory parts feeder according to claim 14, said mounting bracket (40) having a sloped surface (41) supporting thereon said one face of said first resilient plate member (5f). A piezoelectrically driven vibratory parts feeder according to any of claims 10 to 15, said second resilient plate member (10f) of said pair or of each said pair of resilient plate members being adjustable in length. A piezoelectrically driven vibratory parts feeder according to claim 16, said second resilient plate member (10f') of said pair or of each said pair of resilient plate members including an elongate holder (31), a slide (32) movably received in said holder (31), and a fastener (34) for locking the slide (32) in position against displacement relative to said holder (31). A piezoelectrically driven vibratory parts feeder according to claim 16, said second resilient plate member (10f'') of said pair or each said pair of resilient plate members including a pair of elongate plate elements (35, 35), and a stud screw (36) interconnecting one ends of said plate elements (35). A piezoelectrically driven vibratory parts feeder according to any of claims 10 to 18, said resilient plate members (5f, 10f) of said pair or each said pair of plate members having the same thickness. A piezoelectrically driven vibratory parts feeder according to any of claims 10 to 19, said first and second resilient plate members (5f, 10f) of said pair or each said pair of resilient plate members having different lengths. A piezoelectrically driven vibratory parts feeder according to claim 20, said second resilient plate member (10f) being longer than said first resilient plate member (5f).

Inventors: KAMISHIMA, YOICHI, KAWAGOE, KAZUO, MASUDA, TAKESHI, OKABE, SAKIICHI, YAGI, SUSUMU
Applicants: YOSHIDA KOGYO K.K.
Application year: 1989
Main classification: B65G27
IPC codes: B65G27, B06B1, H02N2