Patent Publication Number: US-2023154442-A1

Title: Universal joint, coupling rod appratus, and musical instrument pedal device

Description:
FIELD 
     The present disclosure relates to a universal joint, a coupling rod apparatus, and a musical instrument pedal device. 
     DESCRIPTION OF RELATED ART 
     Methods for playing a bass drum by operating left and right pedal devices using two foots are known. For example, operating one pedal device using the left foot produces rotation of a rotary shaft of the other pedal device, which is located at a position separated from the first pedal device. Then, when a beater fixed to the rotary shaft of the other pedal device is rotated, the beater strikes the bass drum. The left and right pedal devices are used, with the rotary shafts of the pedal devices coupled to each other by a coupling rod. In this case, the positions of the left and right pedal devices often differ depending on the physical attribute and preference of a user. Thus, in order for the left and right pedal devices to be flexibly located, a universal joint capable of coupling the coupling rod to the rotary shafts is used with the coupling rod and the rotary shafts angled. 
     The universal joint includes two yokes respectively connected to two rotary members, a spider rotationally coupled to the two yokes, and bearings used to couple the two yokes to the spider. The spider is coupled to the two yokes by the bearings such that the spider is rotatable about two axes, which are orthogonal to each other. The universal joint is configured to change the coupling angle between the coupling rod and the rotary shaft and transmit rotation about the axes between the coupling rod and the rotary shaft. 
     For example, the following universal joints applied to a drum twin pedal or the like have been proposed. The specifications of U.S. Pat. Nos. 7,633,000, 8,556,735, and 6,878,068 each disclose a universal joint that includes two yokes, an annular spider disposed outside the two yokes, and four bearings. The specification of U.S. Pat. Nos. 8,110,731 or 7,641,560 discloses a universal joint that includes two yokes, a block-shaped spider disposed inside the two yokes, and four bearings. 
     The spider disclosed in U.S. Pat. No. 7,633,000 is a single component. The spider disclosed in U.S. Pat. No. 8,556,735 is formed by coupling two segments to each other. The spiders disclosed in the two documents each include four holes that radially extend through the spider and are arranged at regular intervals. The four holes of the spider each include a bearing and a shaft. The shaft is press-fitted into the inner ring of the bearing and the holes in a yoke tip. The outer ring of the bearing is fixed in the holes of the spider. The spider of U.S. Pat. No. 6,878,068 includes a spider body and four lid members coupled to the spider body. The spider disclosed in this document also includes four holes that radially extend through the spider and are arranged at regular intervals. The four holes of the spider each include a bearing and a protrusion of a yoke tip. The inner ring of the bearing is fixed to the protrusion at the yoke tip. The outer ring of the bearing is fixed in the holes of the spider. 
     The spider disclosed in U.S. Pat. No. 8,110,731 includes a hole which is located in each of four side surfaces that are coupled to the yoke and in which a bearing is arranged. The yoke includes threaded holes at positions corresponding to the holes in the spider. The inner ring of the bearing is fixed to the tip of a threaded pin fastened to the threaded holes in the yoke. The outer ring of the bearing is fixed in the holes of the spider. The spider disclosed in U.S. Pat. No. 7,641,560 includes a threaded hole in each of four side surfaces that are coupled to the yoke. The yoke includes threaded holes at positions corresponding to the threaded holes of the spider. The inner ring of the bearing, together with a ring-shaped spacer, is fixed to a side surface of the spider by a screw. The outer ring of the bearing is fixed to the threaded holes of the yoke. 
     The spiders disclosed in U.S. Pat. Nos. 7,633,000, 8,556,735, and 6,878,068 are annular bodies having a larger outer diameter than the yoke. That is, these spiders are relatively large in size and weight. Thus, a larger rotational moment force tends to be generated when a rotational force is transmitted between the two yokes. For this reason, in the twin pedal using the universal joints disclosed in U.S. Pat. Nos. 7,633,000, 8,556,735, and 6,878,068, when a bass drum is played, the feeling felt when a pedal is depressed with the left foot or when the depressed left pedal returns tends to be different from the feeling felt when a pedal is operated with the right foot. Thus, playing the bass drum using the left and right pedal devices produces a feeling of awkwardness. Accordingly, a good feeling during operation is not obtained. In addition, in the spider disclosed in U.S. Pat. Nos. 7,633,000 or 8,556,735, the positional accuracy and the dimensional accuracy are strictly required for the four bearing-fixing holes in a single component or two segments. This is because, when the bearings are simultaneously fixed in the four holes, the bearing to be disposed in the holes cannot be fixed if the diameter of one hole is relatively large or the position of one hole is shifted. The spider disclosed in U.S. Pat. No. 6,878,068 has a complicated structure due to a relatively large number of components used for the spider. 
     In the universal joint disclosed in U.S. Pat. No. 8,110,731, when the threaded pin is tightened, an axial load tends to be applied to the inner ring of the bearing. Thus, depending on the degree of tightening of the threaded pin, the bearing may be locked. In the universal joint disclosed in U.S. Pat. No. 7,641,560, the inner and outer rings of the bearing are intentionally twisted in order to eliminate backlash. However, this may also cause the bearing to be locked by an axial load depending on the degree of tightening of a screw or the dimensional accuracy of the components. Further, in the universal joint disclosed in U.S. Pat. No. 7,641,560, since the outer ring of the bearing is fixed to the yoke, the rotational moment force tends to be larger than in the universal joint disclosed in U.S. Pat. No. 8,110,731, in which the outer ring of the bearing is fixed to the spider. 
     SUMMARY 
     It is an objective of the present disclosure to provide a universal joint, a coupling rod apparatus, and a musical instrument pedal device that are capable of reducing a rotational moment force and reducing manufacturing burdens. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     According to an aspect of the present disclosure, a universal joint is provided. The universal joint includes two yokes respectively connected to two rotary members, a spider rotationally coupled to the two yokes, and a bearing disposed at a portion that couples the two yokes to the spider, the bearing rotationally supporting the spider. The spider is configured to be arranged in a space defined by inner surfaces of the two yokes and allow an outer ring of the bearing to be fixed to the spider. 
     According to another aspect of the present disclosure, a universal joint is provided. The universal joint includes two yokes respectively connected to two rotary members, the yokes each including an insertion hole into which a corresponding one of the rotary members is inserted, a spider rotationally coupled to the two yokes. At least one of the two yokes includes a fastener that fixes the rotary member to the insertion hole and a pushing member disposed in the insertion hole. The pushing member, when pushed by the fastener, presses the rotary member against a wall surface of the insertion hole and fixes the rotary member to the wall surface. The pushing member is configured to come into planar contact with the rotary member. 
     According to a further aspect of the present disclosure, a coupling rod apparatus is provided. The coupling rod apparatus is configured to couple a first device, where first rotation is produced, to a second device, where second rotation is produced, and transmit the first rotation to the second device. The coupling rod apparatus includes a universal joint connected to at least one of the first device and the second device and coupling rods coupled to the first device and the second device by the universal joint. The universal joint includes two yokes respectively connected to two rotary members, a spider rotationally coupled to the two yokes, and a bearing disposed at a portion that couples the two yokes to the spider, the bearing rotationally supporting the spider. The spider is configured to be arranged in a space defined by inner surfaces of the two yokes and allow an outer ring of the bearing to be fixed to the spider. 
     According to yet another aspect of the present disclosure, a musical instrument pedal device is provided. The musical instrument pedal device includes pedal devices, the musical instrument pedal device being used with rotary shafts of the pedal devices coupled to each other by a universal joint. The universal joint includes two yokes respectively connected to two rotary members, a spider rotationally coupled to the two yokes, and a bearing disposed at a portion that couples the two yokes to the spider. The bearing rotationally supporting the spider. The spider is configured to be arranged in a space defined by inner surfaces of the two yokes and allow an outer ring of the bearing to be fixed to the spider. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of a twin pedal in which a musical instrument pedal device according to the present disclosure is employed. 
         FIG.  2    is a perspective view of the coupling rod that is disposed on the twin pedal of  FIG.  1   , the coupling rod including universal joints according to the present disclosure. 
         FIG.  3    is a perspective view of a universal joint of  FIG.  1   . 
         FIG.  4    is an exploded perspective view of the universal joint of  FIG.  1   . 
         FIG.  5    is a perspective view of the first yoke included in the universal joint of  FIG.  1   . 
         FIG.  6    is a front view of the universal joint of  FIG.  1   , as viewed in the axial direction of the rotary shaft. 
         FIG.  7    is a front view showing the universal joint of  FIG.  1   , with the rotary shaft tilted about the axis. 
         FIG.  8    is a front view showing the universal joint of  FIG.  1   , with the tilt of the rotary shaft about the axis corrected when pushed by the pushing member. 
         FIG.  9    is a cross-sectional view taken along line  9 - 9  in  FIG.  6   . 
         FIG.  10    is a cross-sectional view taken along line  10 - 10  in  FIG.  6   . 
     
    
    
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     This description provides a comprehensive understanding of the methods, apparatuses, and/or systems described. Modifications and equivalents of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted. 
     Exemplary embodiments may have different forms, and are not limited to the examples described. However, the examples described are thorough and complete, and convey the full scope of the disclosure to one of ordinary skill in the art. 
     In this specification, “at least one of A and B” should be understood to mean “only A, only B, or both A and B.” 
     An embodiment of universal joints  30 ,  40 , a coupling rod apparatus  22 , and a twin pedal  20  according to the present disclosure will now be described with reference to  FIGS.  1  to  10   . The twin pedal  20  corresponds to a musical instrument pedal device. 
     As shown in  FIG.  1   , the twin pedal  20  includes two pedal devices  21 L,  21 R that are operated with left and right feet, respectively, and a coupling rod apparatus  22  that couples the pedal devices  21 L,  21 R to each other. The left pedal device  21 L (first device) includes a left pedal  23 L and a rotary shaft  24 L (rotary member) that rotates when the left pedal  23 L is depressed. The right pedal device  21 R (second device) includes a right pedal  23 R, a first rotary shaft  24 R 1  that rotates when the right pedal  23 R is depressed, and a second rotary shaft  24 R 2  (rotary member). The second rotary shaft  24 R 2  is coupled to the rotary shaft  24 L of the left pedal device  21 L by the coupling rod apparatus  22 . The twin pedal  20  is used with the rotary shaft  24 L of the left pedal device  21 L coupled to the second rotary shaft  24 R of the right pedal device  21 R. 
     Beaters  26 ,  27  that strike a bass drum BD are attached to the first and second rotary shafts  24 R 1 ,  24 R 2 , respectively. In the twin pedal  20 , when the right pedal  23 R is operated with the right foot, the beater  26  rotates together with the first rotary shaft  24 R 1  of the right pedal device  21 R and the bass drum BD is struck by the beater  26 . When the left pedal  23 L is operated with the left foot, the rotary shaft  24 L of the left pedal device  21 L rotates. The rotation is transmitted to the second rotary shaft  24 R 2  of the right pedal device  21 R through the coupling rod apparatus  22 . When the second rotary shaft  24 R 2  is rotated, the beater  27  rotates together with the second rotary shaft  24 R 2  and the bass drum BD is struck by the beater  27 . That is, the coupling rod apparatus  22  is used to transmit, to the second rotary shaft  24 R 2  of the right pedal device  21 R, the rotation of the rotary shaft  24 L produced by the depression of the left pedal  23 L. 
     As shown in  FIGS.  1  and  2   , the coupling rod apparatus  22  includes the left universal joint  30  and the right universal joint  40 . The left universal joint  30  is connected to the rotary shaft  24 L of the left pedal device  21 L. The right universal joint  40  is connected to the second rotary shaft  24 R 2  of the right pedal device  21 R. In addition, the coupling rod apparatus  22  includes a rod assembly  50  (rotary member) that couples the left and right universal joints  30 ,  40  to each other. The rod assembly  50  is formed by connecting multiple coupling rods to each other. Further, the length of the entire rod assembly  50  is configured to be adjusted. 
     The rod assembly  50  includes a first coupling rod  51  (rotary member) coupled to the left universal joint  30  and a second coupling rod  52  (rotary member) coupled to the right universal joint  40 . The second coupling rod  52  has a hexagonal cross-section including an upper surface  52   a  that is wider than the other surfaces. The first coupling rod  51  is tubular and is capable of accommodating the second coupling rod  52 . The second coupling rod  52  is disposed in the first coupling rod  51  in a slidable manner in the axial direction of the first coupling rod  51 . 
     The rod assembly  50  also includes an adjuster  54  used to adjust the length of the entire rod assembly  50 . The adjuster  54  has a bolt  55  used to fix the second coupling rod  52  into the first coupling rod  51 . The adjuster  54  is configured to press a pressing plate  57  against the upper surface  52   a  of the second coupling rod  52  by tightening the bolt  55 . That is, by operating the bolt  55 , the position of the second coupling rod  52  relative to the first coupling rod  51  is changed to adjust the length of the entire rod assembly  50  and the adjusted length is fixed. 
     The rod assembly  50  also includes a memory lock  58  that stores the length of the entire rod assembly  50 . For example, a state used for transportation, in which the second coupling rod  52  is pulled out of the first coupling rod  51 , may be changed to a use state, in which the second coupling rod  52  is inserted into the first coupling rod  51 . In this case, attaching the memory lock  58  to the second coupling rod  52  allows the rod assembly  50  to be easily restored to its original length prior to transportation. 
     The memory lock  58  has a tubular shape with a flat upper surface and is attached to the second coupling rod  52 . A bolt  56  is fastened to the upper surface of the memory lock  58 . The memory lock  58  is configured to directly press the tip of the bolt  56  against the upper surface  52   a  when the bolt  56  is tightened. That is, by operating the bolt  56 , the position of the memory lock  58  relative to the second coupling rod  52  is changed or the position of the memory lock  58  is fixed. 
     The structures of the universal joints  30 ,  40  will now be described with reference to  FIGS.  3  to  8   . The same parts of the right universal joint  40  in the left universal joint  30  will not be described in detail. 
     As shown in  FIGS.  3  and  4   , the universal joint  40  includes a first yoke  41  connected to the second rotary shaft  24 R 2  of the right pedal device  21 R and a second yoke  42  connected to the second coupling rod  52  of the rod assembly  50 . The first yoke  41  rotates together with the second rotary shaft  24 R 2 . The second yoke  42  rotates together with the second coupling rod  52 . The universal joint  40  further includes a spider  43  rotationally coupled to the first and second yokes  41 ,  42  and four bearings used to couple the first and second yokes  41 ,  42  to the spider  43 . The four bearings include two first bearings  44  disposed at a portion that couples the first yoke  41  to the spider  43  and two second bearings  45  disposed at a portion that couples the second yoke  42  to the spider  43 . The two first bearings  44  share an axis C 1  and rotationally support the spider  43  at two positions on the axis C 1 . Likewise, the two second bearings  45  share an axis C 2  and rotationally support the spider  43  at two positions on the axis C 2 . 
     The spider  43  is coupled to the first and second yokes  41 ,  42  by the four bearings such that the spider  43  is rotatable about the two axes C 1 , C 2 , which are orthogonal to each other. Since the spider  43  is coupled to the first and second yokes  41 ,  42  in this manner, the universal joint  40  is configured to change the coupling angle between the second coupling rod  52  and the second rotary shaft  24 R 2 . In addition, the universal joint  40  is configured to transmit rotation about the axes between the second coupling rod  52  and the second rotary shaft  24 R 2 . 
     The structures of the first and second yokes  41 ,  42  will now be described in detail. The same parts of the first yoke  41  in the second yoke  42  will not be described in detail. 
     As shown in  FIGS.  4  to  6   , the first yoke  41  includes a tubular yoke body  41   a  to which the second rotary shaft  24 R 2  is connected, and two (upper and lower) arms  41   b  to which the first bearings  44  are respectively attached. The yoke body  41   a  includes an insertion hole  41   c  having a substantially T-shaped cross-section. The upper half of the insertion hole  41   c  has a rectangular cross-section. The lower half of the insertion hole  41   c  has a substantially semi-circular cross section. 
     A pushing member  46  having a substantially U-shaped cross-section and a flat positioning member  47  having a flat square column are accommodated in the upper part of the insertion hole  41   c.  The pushing member  46  includes a bottom wall  46   a  and two side walls  46   b  extending upward from the opposite side edges of the bottom wall  46   a , respectively. A pushing portion  46   d  having a flat surface  46   c  protrudes from the outer surface of the bottom wall  46   a.  The pushing member  46  is disposed in the insertion hole  41   c , with the pushing portion  46   d  facing downward. 
     The positioning member  47  is disposed in a space between the opposite side walls  46   b  of the pushing member  46 . A threaded hole  47   a  is formed at the center of the positioning member  47 . An insertion hole  41   d  through which a bolt  60  (fastener) is inserted is formed at the center of the upper portion of the yoke body  41   a.  The bolt  60  is inserted through the insertion hole  41   d  and fastened to the threaded hole  47   a  of the positioning member  47 . In this state, the tip of the bolt  60  is in contact with the inner surface of the bottom wall  46   a  of the pushing member  46 . 
     The second rotary shaft  24 R 2  has a substantially circular cross-section with a flat upper surface  28 . The upper surface  28  of the second rotary shaft  24 R 2  is shaped in correspondence with the pushing portion  46   d  of the pushing member  46  accommodated in the insertion hole  41   c  of the yoke body  41   a.  Thus, when the bolt  60  is fastened so that the bottom wall  46   a  of the pushing member  46  is pushed by the tip of the bolt  60 , the upper surface  28  of the second rotary shaft  24 R 2  is pushed by the pushing portion  46   d  of the pushing member  46 . This causes the second rotary shaft  24 R 2  to be pressed against the wall surface  41   e  of the insertion hole  41   c  and thus fitted to the yoke body  41   a  of the first yoke  41 . 
     In this case, the pushing member  46  is pushed from above against the second rotary shaft  24 R 2 , with the flat surface  46   c  in planar contact with the upper surface  28 . That is, the flat surface  46   c  of the pushing member  46  is a contact surface that comes into planar contact with the second rotary shaft  24 R 2  and has a first width W 1 . The pushing member  46  includes rounded corners  46   e  respectively located at the opposite ends of the flat surface  46   c  in the width direction. The upper surface  28  of the second rotary shaft  24 R 2  is a contact surface that comes into planar contact with the pushing member  46  and has a second width W 2 . The second width W 2  is greater than the first width W 1 . The first and second widths W 1 , W 2  are dimensions in a direction orthogonal to an axis C 3  of the bolt  60  and an axis C 4  of the second rotary shaft  24 R 2  when the pushing member  46  is in planar contact with the second rotary shaft  24 R 2 . 
     As shown in  FIGS.  4 ,  5 ,  9 , and  10   , the arms  41   b  extend from the upper and lower portions of the first yoke  41 , respectively, toward the side opposite the opening of the insertion hole  41   c  of the yoke body  41   a.  A fixing hole  41   f  is formed in the vicinity of the tip of each arm  41   b.  Each fixing hole  41   f  is used to fix the corresponding first bearing  44  together with a ring-shaped collar  49 . Press-fitting the tips of fixing pins  48  respectively into the fixing holes  41   f  causes an inner ring  44   a  of each first bearing  44  and the corresponding collar  49  to be fixed between the head of the fixing pin  48  and the arm  41   b.  In this state, the fixing pin  48  fixes the inner ring  44   a  of the first bearing  44  to the inner surface of the arm  41   b  in the axial direction of the first bearing  44 . In the second yoke  42 , the same method is employed to cause an inner ring  45   a  of each second bearing  45  and the corresponding collar  49  to be fixed between the head of a fixing pin  48  and an arm  42   b.  In the present embodiment, the first bearings  44  and the second bearings  45  are ball bearings in which balls  44   c,    45   c  are disposed between inner rings  44   a,    45   a  and outer rings  44   b,    45   b,  respectively. 
     The structure of the spider  43  will now be described in detail. 
     As shown in  FIGS.  3  and  4   , the spider  43  includes multiple components and has a substantially hexahedral shape. The spider  43  is divided into a spider body  61  and a first lid  62  by first dividing surfaces  61   a,    62   a,  and is divided into the spider body  61  and a second lid  63  by second dividing surfaces  61   b,    63   a.  The spider  43  is configured to allow the outer rings  44   b,    45   b  of the four bearings  44 ,  45  to be fixed to the spider  43  by coupling the spider body  61  to the first and second lids  62 ,  63 . To couple the spider body  61  to the first and second lids  62 ,  63 , a bolt  70  (fixing member) is used. In addition, the spider  43  is sized such that the spider  43  can be disposed in a space S defined by the inner surfaces of the first and second yokes  41 ,  42 . 
     As shown in  FIGS.  4 ,  9 , and  10   , the spider body  61  is shaped such that the portions to which the first and second lids  62 ,  63  and the four bearings  44 ,  45  are coupled are removed from the spider  43 , which is substantially hexahedral. Thus, the spider body  61  is U-shaped in a side view and ring-shaped in a front view with reference to the direction in which the first and second lids  62 ,  63  are coupled to the spider body  61 . 
     The first dividing surface  61   a  of the spider body  61  includes a first accommodation portion  61   d   1  (recess) in which the outer rings  44   b  of the two first bearings  44  are arranged. In the spider  43 , the first accommodation portion  61   d   1  is shaped in correspondence with the first lid  62  and the first bearings  44 . The two inner end surfaces of the first accommodation portion  61   d   1  have an arcuate shape so as to partially coincide with the outer circumferential surfaces of the outer rings  44   b  of the first bearings  44 . 
     The second dividing surface  61   b  of the spider body  61  includes a second accommodation portion  61   d   2  (recess) in which the outer rings  45   b  of the two second bearings  45  are arranged. In the spider  43 , the second accommodation portion  61   d   2  is shaped in correspondence with the second lid  63  and the second bearings  45 . The two inner end surfaces of the second accommodation portion  61   d   2  have an arcuate shape so as to partially coincide with the outer circumferential surfaces of the outer rings  45   b  of the second bearings  45 . 
     A first insertion hole  62   b  through which the bolt  70  is inserted and a second insertion hole  62   c  having a larger diameter than the first insertion hole  62   b  are formed at the center of the first lid  62 . The second insertion hole  62   c  connects to the first insertion hole  62   b.  The first dividing surface  62   a  of the first lid  62  includes a recessed first contact portion  62   d  with which the outer rings  44   b  of the two first bearings  44  are brought into contact. The first contact portion  62   d  has an arcuate shape so as to partially coincide with the outer circumferential surfaces of the outer rings  44   b  of the first bearings  44 . 
     A threaded hole  63   c  to which the tip of the bolt  70  is fastened is formed at the center of the second lid  63 . The second dividing surface  63   a  of the second lid  63  includes a recessed second contact portion  63   d  with which the outer rings  45   b  of the two second bearings  45  are brought into contact. The second contact portion  63   d  has an arcuate shape so as to partially coincide with the outer circumferential surfaces of the outer rings  45   b  of the second bearings  45 . The second lid  63  is the same as the first lid  62  except that the second lid  63  has the threaded hole  63   c  instead of the first and second insertion holes  62   b,    62   c.    
     The spider body  61 , the first lid  62 , and the second lid  63  are coupled to each other in a state of being arranged on a straight line L 1  that is orthogonal to the axis C 1  of the first bearing  44  and the axis C 2  of the second bearing  45 . The first and second lids  62 ,  63  are coupled to the spider body  61  at positions facing the spider body  61 . The second lid  63  is coupled to the spider body  61  in an orientation different from that of the first lid  62  by  90  degrees. The spider body  61 , the first lid  62 , and the second lid  63  are coupled to each other by the bolt  70  in the direction orthogonal to the axes C 1 , C 2 . The bolt  70  is arranged such that an axis C 5  of the bolt  70  coincides with the straight line L 1 , with the first and second lids  62 ,  63  fixed to the spider body  61 . 
     The operation of the universal joints  30 ,  40  will now be described. First, the operation in the method for coupling the universal joints  30 ,  40  will be described with reference to  FIGS.  4 ,  9 , and  10   . 
     As shown in  FIGS.  4 ,  9 , and  10   , the fixing pins  48  are used to fix the inner rings  44   a  of the first bearings  44  to the inner surface of the first yoke  41  in the axial direction of the first bearings  44  and attach the first bearings  44  to the inner surface of the first yoke  41 . Likewise, the fixing pins  48  are used to fix the inner rings  45   a  of the second bearings  45  to the inner surface of the second yoke  42  in the axial direction of the second bearings  45  and attach the second bearings  45  to the inner surface of the second yoke  42 . 
     Next, the first yoke  41  to which the first bearings  44  are attached and the second yoke  42  to which the second bearings  45  are attached are coupled to the spider body  61 . The first bearings  44  of the first yoke  41  are first fitted into the first accommodation portion  61   d   1  of the spider body  61 . Then, the first lid  62  is fitted into the first accommodation portion  61   d   1  so as to cover the two first bearings  44  arranged in the first accommodation portion  61   d   1 . Likewise, the second bearings  45  of the second yoke  42  are fitted into the second accommodation portion  61   d   2  of the spider body  61 . Then, the second lid  63  is fitted into the second accommodation portion  61   d   2  so as to cover the two second bearings  45  arranged in the second accommodation portion  61   d   2 . 
     Subsequently, the bolt  70  is used to fix the first and second lids  62 ,  63  to the spider body  61 . The bolt  70  is fastened to the threaded hole  63   c  of the second lid  63  until a head  70   a  is brought into contact with a step  62   e  at the boundary between the first insertion hole  62   b  and the second insertion hole  62   c.  Tightening the bolt  70  fixes the first and second lids  62 ,  63  to the spider body  61 . This causes the outer rings  44   b  of the first bearings  44  to be held by the first lid  62  and the spider body  61 . As a result, the outer rings  44   b  of the two first bearings  44  are fixed on the first dividing surface  61   a  of the spider body  61  and the first dividing surface  62   a  of the first lid  62 . Likewise, the outer rings  45   b  of the second bearings  45  are held by the second lid  63  and the spider body  61 . As a result, the outer rings  45   b  of the two second bearings  45  are fixed on the second dividing surface  61   b  of the spider body  61  and the second dividing surface  63   a  of the second lid  63 . In this manner, the outer rings  44   b,    45   b  of the first and second bearings  44 ,  45  are fixed to the spider  43 , and the spider  43  is coupled to the first and second yokes  41 ,  42  by the first and second bearings  44 ,  45 . 
     In this case, the direction in which the bolt  70  is tightened is orthogonal to the direction in which the fixing pins  48  are press-fitted (i.e., the axes C 1 , C 2  of the first and second bearings  44 ,  45 ). The load produced when the first and second lids  62 ,  63  are coupled to the spider body  61  using the bolt  70  acts in the direction orthogonal to the axes C 1 , C 2  of the first and second bearings  44 ,  45 . Thus, at the portion that couples the first and second yokes  41 ,  42  to the spider  43 , the load produced by tightening the bolt  70  is less likely to act in the same direction as the axes C 1 , C 2  of the first and second bearings  44 ,  45 . Accordingly, during coupling of the universal joints  30 ,  40 , the inner rings  44   a  and  45   a  and the outer rings  44   b  and  45   b  of the first and second bearings  44 ,  45  are less likely to be twisted by the tightening of the bolt  70 . 
     In addition, the spider  43  of each of the universal joints  30 ,  40  is sized such that the spider  43  can be disposed in the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . That is, the spider  43  is sized such that the spider  43  can be disposed in a space having a smaller size than the first and second yokes  41 ,  42 . Thus, the universal joint  30 ,  40  have a reduced rotational moment force generated when a rotational force is transmitted between the first and second yokes  41 ,  42 . Accordingly, in the twin pedal  20  using the universal joints  30 ,  40 , the following advantage is achieved when the bass drum BD is played. The feeling felt when the left pedal  23 L is depressed with the left foot or when the depressed left pedal  23 L returns is less likely to be different from the feeling felt when the right pedal  23 R is operated with the right foot. This eliminates a feeling of awkwardness when the bass drum BD is played using the left and right pedal devices  21 L,  21 R. As a result, a good feeling during operation is obtained. 
     The operation produced when the second rotary shaft  24 R 2  of the pedal device  21 R is connected to the universal joint  40  will now be described with reference to  FIGS.  6 ,  7 , and  8   . 
       FIG.  6    shows a state in which the second rotary shaft  24 R 2  is not tilted about the axis (C 4 ) before the bolt  60  is tightened. In this state, the flat surface  46   c  of the pushing member  46  and the upper surface  28  of the second rotary shaft  24 R 2  are substantially parallel to each other. This allows the flat surface  46   c  of the pushing member  46  to easily come into planar contact with the upper surface  28  of the second rotary shaft  24 R 2  by tightening the bolt  60 . As shown in  FIG.  8   , when the pushing member  46  is pushed from above against the second rotary shaft  24 R 2 , the second rotary shaft  24 R 2  is pressed against the wall surface  41   e  of the insertion hole  41   c.    FIG.  7    shows a state in which the second rotary shaft  24 R 2  is tilted about the axis (C 4 ) before the bolt  60  is tightened. In this state, the flat surface  46   c  of the pushing member  46  and the upper surface  28  of the second rotary shaft  24 R 2  are not parallel to each other. 
     In the present embodiment, the second width W 2  of the upper surface  28  of the second rotary shaft  24 R 2  is greater than the first width W 1  of the flat surface  46   c  of the pushing member  46 . Further, the rounded corners  46   e  are respectively disposed at the opposite ends of the flat surface  46   c  in the width direction. Thus, when the bolt  60  is tightened from the state shown in  FIG.  7   , the upper surface  28  of the second rotary shaft  24 R 2  is pushed by one of the corner portions  46   e  of the flat surface  46   c.  This causes the second rotary shaft  24 R 2  to rotate about the axis (C 4 ) in the direction represented by the arrow in  FIG.  7    until the flat surface  46   c  of the pushing member  46  comes into planar contact with the upper surface  28  of the second rotary shaft  24 R 2 . As a result, even when the flat surface  46   c  of the pushing member  46  is not parallel to the upper surface  28  of the second rotary shaft  24 R 2 , the pushing member  46  and the second rotary shaft  24 R 2  are smoothly brought into planar contact with each other as shown in  FIG.  8   . That is, even in a state where the second rotary shaft  24 R 2  is tilted about the axis (C 4 ), the tilt of the second rotary shaft  24 R 2  about the axis (C 4 ) is corrected when the second rotary shaft  24 R 2  is pushed by the pushing member  46 . 
     Accordingly, the present embodiment provides the following advantages. 
     (1) The spider  43  is sized such that the spider  43  can be disposed in the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . That is, the spider  43  is sized such that the spider  43  can be disposed in a space having a smaller size than the first and second yokes  41 ,  42 . Thus, the universal joints  30 ,  40  have a reduced rotational moment force generated when a rotational force is transmitted between the first and second yokes  41 ,  42 . 
     (2) The outer rings  44   b,    45   b  of the first and second bearings  44 ,  45  are fixed to the spider  43  by coupling multiple components to each other in the direction orthogonal to the axes C 1 , C 2  of the first and second bearings  44 ,  45 . The load produced by coupling the components acts in the direction orthogonal to the axes C 1 , C 2  of the first and second bearings  44 ,  45 . Thus, at the portion that couples the first and second yokes  41 ,  42  to the spider  43 , the load is less likely to act in the same direction as the axes C 1 , C 2  of the first and second bearings  44 ,  45 . This facilitates coupling of the universal joints  30 ,  40  without locking the first and second bearings  44 ,  45 . As a result, manufacturing burdens are reduced. 
     (3) The first dividing surface  61   a  of the spider body  61  includes the recessed first accommodation portion  61   d   1 , in which the outer rings  44   b  of the first bearings  44  are arranged. Further, the second dividing surface  61   b  of the spider body  61  includes the recessed second accommodation portion  61   d   2 , in which the outer rings  45   b  of the second bearings  45  are arranged. This structure allows for coupling of the universal joints  30 ,  40  with the first and second bearings  44 ,  45  arranged in the spider  43 . As a result, the universal joints  30 ,  40  have a compact shape in the vicinity of the portion that couples the first and second yokes  41 ,  42  to the spider  43 . This further reduces the rotational moment force. 
     (4) The spider  43  is formed by coupling the spider body  61  to the first and second lids  62 ,  63 . In this structure, first, the first and second bearings  44 ,  45  are respectively arranged in the first and second accommodation portions  61   d   1 ,  61   d   2  of the spider body  61 . Then, the first and second lids  62 ,  63  are coupled to the spider body  61  so as to cover the first and second bearings  44 ,  45  in the first and second accommodation portions  61   d   1 ,  61   d   2 . This allows the outer rings  44   b,    45   b  of the first and second bearings  44 ,  45  to be fixed to the spider  43  at the same time when the spider  43  is manufactured by coupling multiple components. Accordingly, the efficiency of coupling the universal joints  30 ,  40  is improved. As a result, manufacturing burdens are further reduced. 
     (5) The two first bearings  44 , which share the axis C 1 , are fixed at two positions on the axis C 1  by the first dividing surfaces  61   a,    62   a  of the spider  43 . Further, the two second bearings  45 , which share the axis C 2 , are fixed at two positions on the axis C 2  by the second dividing surfaces  61   b,    63   a  of the spider  43 . In this structure, the number of bearings  44  that need to be positioned relative to the spider  43  is reduced by half as compared with a conventional structure in which a component of the spider  43  has four holes used to fix bearings. Accordingly, even if the dimensional accuracy of the components is lower than that of the conventional spider, the outer rings  44   b  of the bearings  44  are easily pressed against and fixed to the spider  43 . This further reduces manufacturing burdens. 
     (6) The first lid  62  is fitted into the first accommodation portion  61   d   1  so as to cover the two first bearings  44  arranged in the first accommodation portion  61   d   1 . Likewise, the second lid  63  is fitted into the second accommodation portion  61   d   2  so as to cover the two second bearings  45  arranged in the second accommodation portion  61   d   2 . In this structure, the first lid  62 , which is used to fix the two first bearings  44  to the spider  43 , is a single component. Likewise, the second lid  63 , which is used to fix the two second bearings  45  to the spider  43 , is a single component. Thus, as compared with when each of two bearings is fixed using a different lid, the number of components is reduced and the structures of the universal joints  30 ,  40  are simplified. This further improves the efficiency of coupling the universal joints  30 ,  40 . 
     (7) The spider body  61 , the first lid  62 , and the second lid  63  are coupled to each other in a state of being arranged on the straight line L 1 , which is orthogonal to the axis C 1  of the first bearings  44  and the axis C 2  of the second bearings  45 . This structure allows the center of gravity of the spider  43  to be set in the vicinity of the center of the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . Accordingly, since the center of gravity is set in the vicinity of the center of the universal joints  30 ,  40 , the rotational moment force in the universal joints  30 ,  40  is further reduced. 
     (8) The first and second lids  62 ,  63  are coupled to the spider body  61  at positions facing the spider body  61 . This easily makes the center of gravity of the spider  43  closer to the center of the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . 
     (9) The bolt  70  is arranged such that the axis C 5  of the bolt  70  coincides with the straight line L 1 , with the first and second lids  62 ,  63  fixed to the spider body  61 . In this structure, the arrangement of the bolt  70 , the spider body  61 , and the lids  62 ,  63  on the same straight line makes the center of gravity of the spider  43  closer to the center of the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . Accordingly, since the center of gravity is made closer to the center of the universal joints  30 ,  40 , the rotational moment force in the universal joints  30 ,  40  is further reduced. 
     (10) The fixing pins  48  are used to fix the inner rings  44   a  of the first bearings  44  to the inner surface of the first yoke  41  in the axial direction of the first bearings  44 . Likewise, the fixing pins  48  are used to fix the inner rings  45   a  of the second bearings  45  to the inner surface of the second yoke  42  in the axial direction of the second bearings  45 . In this structure, the direction in which the inner rings  44   a,    45   a  of the first and second bearings  44 ,  45  are fixed to the inner surfaces of the first and second yokes  41 ,  42  is orthogonal to the direction in which the outer rings  44   b,    45   b  of the first and second bearings  44 ,  45  are fixed to the spider  43 . That is, during coupling of the universal joints  30 ,  40 , load is less likely to act in the same direction on the inner rings  44   a,    45   a  and the outer rings  44   b,    45   b  of the first and second bearings  44 ,  45 . This facilitates coupling of the universal joints  30 ,  40  without twisting the inner rings  44   a,    45   a  and the outer rings  44   b,    45   b  of the first and second bearings  44 ,  45 . As a result, manufacturing burdens are further reduced. 
     (11) A method may be employed to fix a rotary member to the wall surface of an insertion hole of a yoke by directly pressing the tip of a fastener (e.g., screw or bolt) against the rotary member. In the present disclosure, the pushing member  46  is pushed from above against the second rotary shaft  24 R 2  by the bolt  60 , with the flat surface  46   c  in planar contact with the upper surface  28 . In this case, an axial force produced by the bolt  60  is transmitted to the second rotary shaft  24 R 2 , in a state where the pushing member  46  pushed by the bolt  60  is in planar contact with the second rotary shaft  24 R 2 . This allows the second rotary shaft  24 R 2  to be pressed against and fixed to the wall surface  41   e  of the insertion hole  41   c.  In this case, as compared with the conventional fixing method, an axial force produced by the fastener is transmitted to a wider area of the rotary member. This ensures that the second rotary shaft  24 R 2  is fixed to the insertion hole  41   c  of the first yoke  41 . 
     (12) The upper surface  28  of the second rotary shaft  24 R 2  is a contact surface that comes into planar contact with the pushing member  46  and has a second width W 2 , which is greater than the first width W 1  of the flat surface  46   c.  In this structure, when an axial force produced by the bolt  60  causes the pushing member  46  to be pushed against the second rotary shaft  24 R 2 , the corners  46   e  at the opposite ends of the flat surface  46   c  in the width direction push the upper surface  28  of the second rotary shaft  24 R 2 . Thus, even when the second rotary shaft  24 R 2  is tilted about the axis C 4 , the pushing member  46  and the second rotary shaft  24 R 2  are smoothly brought into planar contact with each other. That is, even when the second rotary shaft  24 R 2  is tilted about the axis (C 4 ), the tilt of the second rotary shaft  24 R 2  about the axis (C 4 ) is corrected when the second rotary shaft  24 R 2  is pushed by the pushing member  46 . This improves the efficiency of fixing the second rotary shaft  24 R 2  to the insertion hole  41   c  of the first yoke  41  using the bolt  60 . 
     In addition, the pushing member  46  includes the rounded corners  46   e,  which are respectively located at the opposite ends of the flat surface  46   c  in the width direction. In this structure, the rounded shapes of the corners  46   e  of the pushing member  46  allow the corners  46   e  of the pushing member  46  to smoothly contact the second rotary shaft  24 R 2 . That is, this structure limits situations in which the corners  46   e  of the pushing member  46  are caught by the upper surface  28  of the second rotary shaft  24 R 2 . Thus, the pushing member  46  smoothly pushes the second rotary shaft  24 R 2 . Accordingly, the pushing member  46  and the second rotary shaft  24 R 2  are easily brought into planar contact with each other. 
     The above embodiment may be modified as follows. 
     In the present embodiment, the spider  43  is supported by the two first bearings  44  at two positions on the axis C 1  of the first bearings  44  and by the two second bearings  45  at two positions on the axis C 2  of the second bearings  45 . Instead, for example, two bearings respectively arranged on the two axes C 1 , C 2 , which are orthogonal to each other, may be fixed to the spider  43 . That is, the universal joints  30 ,  40  may be coupled by fixing two bearings having no shared axis to the spider  43 . 
     In the present embodiment, the spider  43  is substantially hexahedral. Instead, the spider  43  may have another three-dimensional (e.g., spherical or polyhedral) shape as long as the spider  43  is shaped so as to be rotatable in the space S, which is defined by the inner surfaces of the first and second yokes  41 ,  42 . 
     In the present embodiment, a structure may be employed in which the first lid  62  is divided into two lid pieces and the two lid pieces are coupled to the spider body  61  so as to respectively cover the two first bearings  44  arranged in the first accommodation portion  61   d   1 . The second lid  63  may also be divided into two lid pieces and coupled to the spider body  61  in the same manner. 
     In the present embodiment, the bolt  70  is used to fix the first and second lids  62 ,  63  to the spider body  61 . Instead, a fixing pin may be used. In this case, after the fixing pin is inserted through the first insertion hole  62   b  and the second insertion hole  62   c,  the tip of the fixing pin is press-fitted into a fixing hole of the second lid  63 . Instead of the bolt  70  or a fixing member (e.g., fixing pin), magnets, adhesives, tapes, or the like may be used to fix the first and second lids  62 ,  63  to the spider body  61 . 
     In the present embodiment, the fixing pins  48  are used to fix the inner rings  44   a ,  45   a  of the first and second bearings  44 ,  45  on the inner surfaces of the first and second yokes  41 ,  42 . Instead, bolts may be used. In this case, the first and second bearings  44 ,  45  are fixed to the inner surfaces of the first and second yokes  41 ,  42  by forming threaded holes in the inner surfaces of the first and second yokes  41 ,  42  and fastening the bolts to the threaded holes. 
     In the present embodiment, the pushing portion  46   d  may be omitted from the pushing member  46 . In this case, the bottom wall  46   a  of the pushing member  46  is made flat for the bottom wall  46   a  to come into planar contact with the upper surface  28  of the second rotary shaft  24 R 2 . 
     In the present embodiment, the first bearing  44  and the second bearing  45  do not have to be ball bearings. Instead, the first bearing  44  and the second bearing  45  may be any rolling bearings in which rolling elements other than balls are disposed between the inner ring and the outer ring. 
     In the present embodiment, the corners  46   e  of the pushing member  46  do not have to be rounded and may be chamfered to have an obtuse angle. 
     In the present embodiment, the musical instrument pedal device is applied to the twin pedal  20 , including the two pedal devices  21 L,  21 R respectively operated by the left and right feet. Instead, the musical instrument pedal device may be applied to a drum system for playing a remote bass drum. 
     Various changes in form and details may be made to the examples above without departing from the spirit and scope of the claims and their equivalents. The examples are for the sake of description only, and not for purposes of limitation. Descriptions of features in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined differently, and/or replaced or supplemented by other components or their equivalents. The scope of the disclosure is not defined by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.