Lock pin mechanism

A lock pin assembly for a collar bracket which is capable of engaging and releasing a member to be fixed. The lock pin is generally of cylindrical shape having, at one end, a neck portion of a small diameter, a pair of parallel excisions adjacent to the neck portion, the boundary between the neck portion and the excisions forming a shoulder, and, at the opposite end, a tapered tip. The collar bracket is provided with a pair of outwardly extending flanges, each having a hole for housing a pair of respective lock pins in opposite orientation. The lock pins are freely rotatable in the flange holes and are biased rearward by springs. A plate with a U-shaped cut-out is provided adjacent each flange for engaging the shoulder of each respective lock pin when the lock pin is moved forward against its bias and then rotated. When the lock pin is moved inward and rotated to such position, its tapered tip engages the member to be fixed.

BACKGROUND OF THE INVENTION 
The present invention relates to a lock pin assembly, and more particularly 
to a lock pin which is freely rotatable and which may engage or release a 
member to be fixed by the insertion or withdrawal of the tip portion of 
the lock pin into a hole in the member to be fixed. 
In a stand which consists of a plurality of tubular members, such as the 
musical instrument stand shown in FIG. 1, it is necessary to provide a 
reinforcing member for the assembly. It is desirable that the reinforcing 
member be easily and simply installed or detached to facilitate assembly 
and dismantling of the stand. The lock pin assembly of the present 
invention provides this feature. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a lock pin assembly is provided 
on a collar bracket which is capable of engaging and releasing a member to 
be fixed through the rotation of the lock pin. The lock pin has a neck 
portion of a small diameter, a pair of parallel excisions adjacent to the 
neck portion, the boundary between the neck portion and the excisions 
forming a shoulder, and a tip portion of decreasing diameter at the 
opposite end of the lock pin. The tip portion of the lock pin is inserted 
into an engagement hole in the member to be fixed. The lock pin is freely 
rotatable in an aperture provided in the collar bracket. The collar 
bracket includes a plate with a U-shaped cut-out portion which cooperates 
with the shoulder of the lock pin to lock the lock pin in the engage 
position. The lock pin is biased rearwardly in the disengage position by a 
spring in the bracket. The lock pin is moved from the engage to the 
disengage position by appropriate rotation so that the parallel excisions 
of the lock pin line up with the cut-out portion of the plate, thereby 
releasing the shoulder and allowing the lock pin to move rearwardly. 
Other features of the invention will be apparent from the following 
description of a preferred embodiment of the invention considered with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The stand structure shown in FIG. 1 may be used as a stand for a musical 
instrument such as a keyboard. The stand has been constructed so as to be 
easily assembled and dismantled for stage performance. 
As shown in FIG. 1, the stand comprises tubular members 10, a respective 
bracket 11 for each of the pairs of the legs of the stand, connective 
brackets 12 for coupling horizontal ones of the tubular members to the leg 
portion of the stand, sliders 13 for holding items, and at least one 
reinforcement rod member 20. 
As previously mentioned, the lock pin assembly of the present invention may 
be utilized for securing and releasing the reinforcement rod member 20 to 
the stand structure. Obviously, however, the lock pin assembly of the 
present invention may also be utilized in a wide variety of other 
applications; i.e., the invention may be used for joining to any type of 
structure, not related to musical instruments, supports or stands. In the 
following discussion, the reinforcement rod member is used as an example 
of a member to be fixed by the lock pin. 
Referring now to FIG. 2, the reinforcing rod member 20 is used as a brace 
for the reinforcement of two tubular members 10, which have been connected 
at a right angle by a bracket 12. Reinforcing rod member 20 comprises a 
reinforcing rod 21 and a respective collar bracket 22 for securing each 
end of the reinforcing rod 21 to the respective tubular members 10. In the 
example shown, the collar bracket 22 is fixed to tubular member 10, and 
rod 21 is the member to be fixed to collar bracket 22. 
Referring now to FIG. 3, collar bracket 22 is, broadly, a split ring, split 
at opening 23, with aligned flanges 24 provided on both sides of opening 
23. Flanges 24 are drawn together by a tightening bolt 25 to securely fix 
collar bracket 22 to any given location along tubular member 10. 
On the opposite side of the collar bracket 22 from opening 23, a pair of 
lock pins 30 are held opposed to and movable toward each other, freely 
rotatable in respective fixing flanges 26 and 27 for the engagement of 
reinforcing rod 21. 
Reinforcing rod 21 terminates in a widened end piece 28a with opposite 
flats that seat loosely against flanges 26 and 27. An engagement hole 29 
extends through end piece 28a which can be disposed between flanges 26 and 
27 of the collar bracket, and the lock pins 30 can extend into both ends 
of the engagement hole 29. 
As is evident from FIG. 4, lock pin 30 includes a neck portion 32, a main 
body 33, and a shoulder therebetween. The neck portion 32 has a diameter 
which is smaller than that of the main body 33. The main body 33 has a 
tapered end 34 which is inserted into engagement hole 29 of reinforcing 
rod 21 for engaging the reinforcing rod 21. In addition, lock pin 30 has, 
on main body 33, adjacent to the shoulder, a pair of excisions 35 which 
form parallel flats on opposite sides of the lock pin. 
As shown in FIG. 3, a head knob 31 is attached to the neck portion 32 of 
lock pin 30. The lock pins 30 are held in freely rotatable manner in the 
holes 28 of respective flanges 26 and 27 of the collar bracket 22. The 
lock pin is rearwardly biased by means of a spring 40. 
On the same side of collar bracket 22 as flanges 26 and 27, a respective 
plate 45 having a U-shaped cut-out portion 46 is provided. The lock pin 
may be moved forward through hole 28 when excisions 35 are lined up and 
coincide with notched cut-out portion 46 of the respective plate 45. Plate 
45 also includes an installing hole 48 through which a bolt 49 extends to 
fasten plate 45 to the respective flange of collar bracket 22. Bolt 49 
cooperates with abutments 36, 37 of head knob 31 of the lock pin to serve 
as a stop for the rotation of lock pin 30 as lock pin 30 is rotated from 
an engaged to released position. 
FIGS. 5 and 6 are cross sectional views of the assembly with the head knob 
31 of lock pin 30 removed. FIG. 5 shows pin 30 in engagement hole 29 of 
reinforcing rod 21. FIG. 6 shows lock pin 30 withdrawn from engagement 
hole 29 of reinforcing rod 21. As shown in FIGS. 5 and 6, the excisions 35 
which are provided adjacent to the shoulder of the main body of lock pin 
30 are shaped and sized to pass through cut-out part 46 of plate 45 when 
lock pin 30 is rotated to the appropriate position. 
FIG. 5 shows the lock pin with the excisions 35 aligned with cut-out 
portion 46. Since lock pin 30 is biased rearward by the force of spring 
40, it moves rearward so that tip 34 of lock pin 30 recedes from 
engagement hole 29 and reinforcing rod 21 is released. 
FIG. 6 shows the engagement position of the assembly in which lock pin 30 
has been pushed forward and rotated. As shown, excisions 35 are not 
aligned with cut-out portion 46. As a result, the shoulder of the lock pin 
is engaged by plate 45 to effect locking. In this position, tip 34 of lock 
pin 30 protrudes forward into engagement hole 29 to engage reinforcing rod 
21. 
Abutments 36 and 37 on head knob 31 of lock pin 30 limit the rotation of 
the lock pin between its engagement and release positions by the 
cooperation of abutments 36 and 37 with stopper bolt 49. 
Accordingly, as is evident from the above description, the present 
invention allows the engagement and release of a member to be fixed in a 
simple and easy manner merely by the rotation and forward or rearward 
movement of a lock pin. As a result, the assembly or dismantling of an 
structure, such as a stand for a musical instrument as shown in the 
preferred embodiment, can be effected quickly and easily. 
Although the present invention has been described in connection with a 
preferred embodiment thereof, many other variations and modifications will 
now become apparent to those skilled in the art. It is preferred, 
therefore, that the present invention be limited not by the specific 
disclosure herein, but only by the appended claims.