JP3110900B2 - Belt hanging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for automatically operating a transmission belt between a plurality of pulleys in a manufacturing process or the like.

[0002]

2. Description of the Related Art Power transmission belts are manufactured, for example, during the manufacturing process.
It must be hung at least once between pulleys. By applying an annular belt between a pair of pulleys (usually two, but sometimes three or more) and applying a certain tension, the cover winding process of winding the cloth on the surface is possible. It measures the length, elongation and strength. Even when using the manufactured belt, depending on the application, it may be necessary to hang the belt many times between the same pulleys.

In such a case, a set of pulleys on which a transmission belt is hung is generally variable in positional relationship with each other, that is, the distance between the shafts can be changed. When the belt is put on or taken off, the distance between the shafts is shortened (the pulleys are brought closer to each other) to facilitate the work, and when tension is applied for manufacturing, measurement and use, the distance between the shafts is increased.

[0004] On the other hand, with respect to a side on which a transmission belt is hung between pulleys in an approaching state with a reduced inter-axis distance, that is, a so-called belt hanger, one having the following function is conventionally known. That is, by grasping the top of the belt, the belt is carried from the receiving position (the position where the belt is supplied) to the position of the pulley (the position where the belt surrounds a set of pulleys to be wrapped). . When the belt is positioned around the pulley, the belt is properly wrapped and tensioned by increasing the center distance of the pulley as described above.

[0005]

The above-mentioned conventional belt hanging apparatus has the following disadvantages. That is, a) Since the transmission belt is moved to the position of the pulley by grasping only the uppermost portion, it is difficult to accurately transport the belt to the most desirable position outside the pulley. This is because gripping only a part of the annular belt cannot sufficiently prevent the belt from swinging. Further, since the belt is not entirely restrained but only a part thereof, it is impossible to make the belt sideways. Therefore, when the pulleys are arranged horizontally (horizontally) even in the approaching state, or when the pulley arrangement surface is horizontal (the axis of each pulley is vertical), the belt is hung by such a conventional device. Is impossible.

B) Since the power transmission belt is carried to the pulley position without being particularly deformed (that is, the power transmission belt remains circular except for a slight change in shape due to the effect of gravity), the belt having a short circumference is hung between a plurality of pulleys. Is difficult. If the diameter (inner diameter) of the circular belt is less than the outer dimension (or the diameter of the circumscribed circle) between the pulleys in the approaching state, for example, an operator can help with the hand and extend the belt into an oval shape. Unless it is deformed, it is impossible to hang the belt between the pulleys.

[0007] An object of the present invention is to be able to accurately convey a transmission belt to an optimum position around the pulley regardless of the arrangement of the pulley, and to automatically hang the transmission belt having a shorter circumference than the pulley diameter. The present invention is to provide a belt hanging device capable of performing the above-mentioned operations.

[0008]

According to the present invention, there is provided a belt hooking device comprising: a) a pair of rods having a groove in which a belt can be inserted inside along a longitudinal direction; b) close to a common tangent of an approaching pulley. The pair of bars are opened and closed between a position substantially parallel (each bar is substantially parallel to each common tangent line) (which is in a closed state) and a position having a greater distance (open state). An opening and closing mechanism, c) a holder to which the rod and the opening and closing mechanism are attached, and d) a moving mechanism to move the holder from the belt receiving position to a position outside the pulley.

In the moving mechanism of this device, d-1) a swing arm is provided rotatably with respect to the fixed member, and d-2) a tip of the swing arm is perpendicular to the turning surface of the arm. The above holder is rotatably mounted via a simple spindle,
d-3) Fixing member so that the holding member rotates in the opposite direction by the same angle as the turning angle of the arm (in other words, so that the relative rotation amount of the holding member with respect to the arm matches the relative rotation amount of the fixing member with respect to the arm). It is more preferable to connect the holder and the holder.

[0010]

The belt hanger of the present invention hangs the transmission belt between predetermined pulleys by handling as follows.

The pair of rods described in a) is opened by the opening and closing mechanism in b), and is first placed together with the holder in c) at the belt receiving position.

When the belt comes inside the rods, the pair of rods is closed by the opening / closing mechanism (into the closed state described above), and the belts are fitted into the grooves inside each. Accordingly, the positional relationship between the pair of bars is such that each bar is located immediately outside the common tangent of the plurality of pulleys in the approaching state and is substantially parallel to each tangent (actually, at this point, the bars are still in position). The position is far from the pulley, but it will be in such a state if it moves as described below), so the belt will be a length that includes the common tangential portion along the inside of these rods from the original circle. It can be deformed into a circular or osby shape.

[0013] The holder is moved by the moving mechanism of d), and the transmission belt is conveyed to the outside of the plurality of pulleys brought into the approach state. The belt is sandwiched between the pair of rods, and is held in such a state that a large part (that is, the above-described common tangential part) of the entire circumference is fitted into the groove inside the rod, so that the movement of the belt is It does not sway or fall off in between, and is securely carried with the rod to the appropriate position outside the pulley. In addition, since it is formed in a shape including a common tangential portion of a plurality of pulleys to be hung (as described above, an oval shape or an oval shape along the arrangement of the pulleys), the outer portion between the pulleys that cannot be hung as it is circular Also, this movement makes it possible to position without problems.

[0014] While the position between the pulleys is changed (change in the distance between the shafts), the holder, the rod, and the like are kept at the above-mentioned movement destination, and after the shafts are opened and the belt is slightly tensioned. Then, the rod is opened by the opening / closing mechanism, separated from the belt, and returned to the original position together with the holder by the moving mechanism.

In the belt hanging device according to the second aspect, the holding tool including the bar and the opening / closing mechanism does not change the direction of the holding tool itself (so-called parallel movement) due to the structure of the moving mechanism.
Move by turning movement. That is, when the swing arm of d-1) is turned by a predetermined angle, the holder rotatably attached to the tip of the arm as in d-2) is the same as the arm turning by the connection shown in d-3). This is because they rotate in the opposite direction by an angle. The holder revolves around the rotation center (fixed member) of the arm with the arm by an angle (θ), so to speak, and at the end of the arm, rotates by (-θ) with respect to the arm. The angle of the holder does not change.

[0016] A moving mechanism by swinging a swing arm or the like is simpler than a linear moving mechanism using a ball screw, a rack and pinion, or the like. Usually, the related equipment must be arranged radially. However, when the holder (functional object) moves without changing the orientation as in this device, each related equipment including the pulley can be arranged in parallel. That is,
For example, since the direction of the belt and the direction of the pulley at the receiving position are parallel to each other, the (longitudinal direction of) the conveyor or the like that supplies the belt to the receiving position is parallel to the axial direction of the pulley of the inspection device or the like. Can be placed in This means that related equipment can be efficiently and compactly laid out in a certain space.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. The example shown in FIGS. 1 to 4 is for a cover winding machine 1 in which a cover cloth A is wound on a surface of a rubber belt B in a process of manufacturing a transmission wrapped V-belt or the like. In this example, a large number of unvulcanized rubber belts B to be wound around the cover are wound one by one between the pulleys 2U and 2D of the cover winding machine 1 by the belt hanging device 30, and the lower pulley 2
By lowering the position of D, an appropriate tension is applied to the belt B.

As shown in FIG. 1, the cover winding machine 1 includes a pulley 2U / 2D connected to a driving means (not shown), a belt hanging device 30 and the like, and a cover cloth A on a belt B on the pulleys 2U / 2D. Rolls 3.3a,
Detector 1 for detecting seam (described later) for cover cloth A
0, a stretching device 5 for spreading the cloth A with a pin for the detection thereof, a supply conveyor 40 for the belt B (see FIG. 3), and the like. Hereinafter, first, the cover winding machine 1 will be entirely described with reference to FIG.

In the cover winding machine 1, the operation of wrapping the surface of the belt B with the belt-shaped cover cloth A is performed over the circumference of the belt B, and the ends of the cloth A are overlapped by several to several tens of millimeters and joined. . By the way, in order to supply the cover cloth A to such a cover winding machine 1, a seam (joint part where cloths are overlapped at the time of manufacturing the cloth A; hereinafter, referred to as a material seam) is present in the cloth A itself. You have to be careful about the position. Since the cloth A is a so-called bias cloth in which fibers are obliquely passed while being a long strip-shaped thing,
It is difficult to eliminate such a material seam in terms of manufacturing, but if this seam overlaps or is too close to the seam between the ends of one circumference wound around the belt B, the seam will be too short. Is very different from other parts in the vicinity of the point where the belt is approached, which is not preferable in terms of the quality of the belt B.

Therefore, in the portion of the cover winding machine 1 where the cover cloth A is supplied, the next cut (cutting) position (scheduled cut position; the end of winding on a certain belt B and the winding on the next belt B) The detection device 10 detects whether or not there is a material seam in a specified dimensional range immediately before and immediately after (at the boundary between the start and the time when the belt B is wound around the seam). At the time of the detection, the cloth A in the area is spread by the spreading device 5 without wrinkles or the like. If it is known that there is a material seam within the dimensional range, the cover winding machine 1 cuts off a part of the cloth A by an appropriate amount with a cutting blade so that the position of the seam is far from the planned cut position. .

The material seam detecting device 10 mainly includes a main body portion and a position adjusting portion. As shown in FIG. 1, the main body portion has a cover cloth A placed on a vertical flat surface 11, , While detecting the displacement of the roller 12 in the horizontal direction while rolling the roller 12, the presence or absence of a joint is known. In order to increase the accuracy by detecting the displacement of the roller 12 in order to increase the accuracy, the roller 12 is moved in the middle of the swing arm 13 that swings around the pin 14.
The sensor 17 for detecting displacement is attached to the arm 1
3 near the swing end. Reference numeral 20 in the figure denotes an air cylinder that moves the swing arm 13 and the pin 14 to the left and right in the figure and presses the roller 12 onto the cloth A.
Reference numeral 5 denotes an air cylinder which moves up and down (vertically) the above portion in order to roll the roller 12 on the cloth A.

On the other hand, the position adjustment portion of the detection device 10 is the position (height) of the flat surface 11 that defines the range of the detection target.
Is adjusted to match the next cut scheduled position in the cover cloth A. As shown in the figure, a vertical guide rod 27 (two on the front side and the other side) and a long And a drive means (not shown) for the same. The base 24 to which the main body is assembled is engaged with the guide rod 27 so as to be able to move up and down in the guide portion 24a.
It is fastened to a part of the belt 28 by b. By driving the belt 28 by an amount corresponding to the measured length of the belt B, the base 24 is moved up and down along the guide rod 27 together with the main body of the apparatus 10 to an appropriate height. The length of the belt B is determined by moving the pulley 2D and applying a predetermined tension to the belt B as described later.
-The cover winding machine 1 automatically measures from the distance between 2D.

As shown in FIG. 1, the stretching device 5 for stretching the cover cloth A on the flat surface 11 in the above detection prevents the cloth A from returning backward just before the cutting blade 4 (upstream side). While the leaf spring 6 is arranged, the blade 7a is attached to a part of the rotatable roll 7 on the base 24 around which the cloth A is wound, and the roll 7 is turned in the reverse direction of the cloth A toward it. A compressed air blowing nozzle 8 is provided to rotate. If the compressed air is blown out from the nozzle 8 until immediately after the cloth A is pulled out while the belt A is pulled out by the rotation of the belt B by the pulleys 2U and 2D, the back-prevention force of the leaf spring 6 and the frictional force from the roll 7 are used. , Cloth A
Can be spread without slack or wrinkles.

To wind the cover cloth A around the belt B in the cover winding machine 1, first, a pair of pulleys 2U
Shrink the space between D and hang the belt B on them. Next, the interval between the pulleys 2U and 2D is widened to give a predetermined tension to the belt B, the tip of the cover cloth A is adhered from the outside, and the pulleys 2U and 2D (one of them) are driven to drive the belt B.
Circulate. Cover cloth A with belt B circulation
The cover cloth A is wound around the entire surface of the belt B by the rolls 3.3a and the like.

The lower pulley 2D of the pulleys 2U and 2D can be moved up and down as indicated by phantom lines. When the pulley 2D is above and close to the pulley 2U, the belt B is easily applied between the pulleys 2U and 2D, and when the position of the pulley 2D is lowered, tension can be applied to the applied belt B. . As a moving mechanism (not shown) of the pulley 2D, for example, a bearing box of the pulley 2D is engaged with a vertical feed screw which is driven to rotate by a motor having a rotation speed detecting means. The belt pulling device 30 to be described later positions one belt B outside the pulleys 2U and 2D so that the upper pulley 2
If it does not meet U, the lower pulley 2D descends and the belt B
And the circumference of the belt B can be known from the position (pulley interval; for example, it can be determined from the number of rotations of the motor).

A belt B is attached to the pair of pulleys 2U and 2D.
The cover winding machine 1 is provided with a belt hanging device 30 and a belt supply conveyor 40 as devices on the side where the belt is wound. One belt B conveyed to a predetermined receiving position by the conveyor 40 is grasped by the belt hanging device 30 and conveyed to the outer peripheral positions of the pulleys 2U and 2D.

The belt supply conveyor 40 is configured as shown in FIGS. That is, the roller 4 at one end
A conveyor belt 41 is stretched between the roller 2 and the other roller (not shown), and an oscillating hanger 43 is provided at the tip end thereof. If the conveyor belt 41 is circulated while the hanger 43 is set to the solid line position on the right side in the figure, the belt B hanging on the hanger 43 is sent from the right until it hits the protrusion 43a of the hanger 43. When the conveyor 40 detects that the belt B has reached the position, the conveyor 40 stops the circulation of the conveyor belt 41, and moves the hanger 43 to the left side of the drawing by the air cylinder 43b to move the leading belt 41 to the virtual line position, that is, It moves to the receiving position by the belt hanging device 30.

The belt hanging device 30 handles the belt B which has reached the receiving position in FIG. 3, and the structure is as follows. That is, first, as shown in FIG. 2, a clamp bar 31 which is a pair of rods capable of sandwiching the belt B is provided.
Is attached to the holder 33 swingably via the pin 31a. Each bar 31 has a base 31b directly connected to a pin 31a.
A groove 31d (see FIG. 4) into which the belt B can be fitted is formed on the inner side (the sides facing each other). The size of the bar 31 is slightly longer so that the large and small belts B having different sizes can be grasped. Further, an opening / closing mechanism 32 is provided between the bases of both bars 31 and the holder 33 so as to open and close the bars 31 around the pins 31a. The mechanism 32 includes an air cylinder 32a connected to the both bars 31 and a synchronization link 32b and a guide pin 32c for opening and closing the both bars 31 symmetrically.
And a pin guide plate 32d. Then, as shown in FIGS. 3 and 4, in order to move the above-described portion from the receiving position to the positions of the pulleys 2U and 2D, the moving device 34 including the swing arm 36 is assembled together with the holder 33.

According to the opening / closing mechanism 32, the clamp bar 31 opens and closes as shown in FIG. That is, when the air cylinder 32a is extended, the bar 31 opens as shown by the imaginary line in the figure, and the belt B in the natural state, that is, the supply conveyor 4
0 (see FIG. 3), it may be located outside the belt B in a state of being hung on the hanger 43, but when the cylinder 32a is contracted, it is closed as shown by the solid line in the drawing, and the belt B is deformed into an oval shape while the groove portion 31d Hold inside. When the bars 31 are closed, the pulleys 2U and 2D close to each other.
(Also shown by phantom lines in FIG. 2), which are located almost parallel to the outside near each common tangent,
The belt B held in the form of an oval has an oval shape along the outside of the pulleys 2U and 2D.

The structure of the moving mechanism 34 will be described below in detail with reference to FIGS. First, a fixing column 35a is provided vertically upward on a frame 35 that is a fixed member. A bearing 36a is attached to the support 35a.
The swing arm 36 is attached rotatably via a,
The expansion and contraction of the air cylinder 36b allows it to pivot in a horizontal plane. At the tip of the arm 36, a support shaft 37 is provided vertically downward.
The holder 33 is attached so as to be freely rotatable horizontally via 7a. As a result, the holder 33 and the clamp bar 31 attached to the holder 33 are turned or revolved by the arm 36 and rotate at the tip thereof.

The moving mechanism 34 further fixes the pulley 38 a with teeth on the fixed support 35 a on the frame 35, while pulling the pulley 38 having the same number of teeth integrally with the holder 33.
b and synchro (toothed) belt 38c
Connected. Since the number of teeth of the pulleys 38a and 38b is the same, the arm 36 turns and the pulley 38 on the side of the support 35a is rotated.
When a relative rotation occurs between the pulley 38a and the arm 36, a rotation (rotation) of an amount (angle) equal to the relative rotation of the pulley 38a with respect to the arm 36 is provided as the relative rotation of the pulley 38b on the holder 33 side with respect to the arm 36. This means that the support 35
The pivot angle of the arm 36 about a (i.e., the holder 3
3 revolution angles. And theta ₁₎ in FIG. 4, the rotation angle (rotation angle of the holder 33 on the arm 36. In FIG. 4 theta ₂₎ and but the size a direction opposite to the same (θ ₁ = -θ ₂₎ As a result, as shown in FIG. 4, the holder 33 changes its position without changing its orientation. And therefore, the direction of the supply conveyor 40 could be made parallel to the axis of the pulleys 2U and 2D of the cover winding machine 1.

The belt B is moved by the belt hanging device 30 or the like.
Is applied to the pulleys 2U and 2D as follows.

The pair of clamp bars 31 are opened and closed by the opening / closing mechanism 3.
2 and placed in the receiving position on the conveyor 40 together with the holder 33 (the state of the right virtual line in FIG. 1 and the virtual line in FIG. 2).

When the belt B comes inside the receiving position, that is, inside the bar 31, the pair of bars 31 is closed by the opening / closing mechanism 32, and the belt B is fitted into and held in the groove portions 31 d inside each (FIG. 2). Solid line state). At this time, the belt B is securely held and does not swing, and has an oval shape that should extend along the outside of the pulleys 2U and 2D as described above.

By rotating the swing arm 36 by expansion and contraction of the air cylinder 36 b of the moving mechanism 34,
By moving the holder 33, the pulley 2U
The belt B is transported outside 2D (see the phantom line in FIG. 2 or the upper part in FIG. 4). At this time, since the belt B has an oval shape as described above and can be moved without changing its direction together with the holder 33 and the bar 31, the pulley 2U
・ Smoothly transported to a position outside 2D. If the pulleys 2U and 2D are not ready, they may be temporarily stopped at a standby position in the middle (the middle solid line position in FIG. 4).

Until the pulley 2D descends to a predetermined position, the holder 33, the bar 31 and the like are kept at the above-mentioned destination, but the pulleys 2U and 2D open and a slight tension is applied to the belt B. At that point, the bar 31 is
Opened by the opening / closing mechanism 32 and separated from the belt B, the holder 3
3 and the like, and is returned to the original standby position and belt receiving position by the moving mechanism 34. Pull away from bar 31, pulley 2U
In the cover winding machine 1, the above-mentioned rollers 3.3a and the detecting device 1 are attached to the belt B to which a predetermined tension is applied on 2D.
The cover cloth A is wound by an action such as 0. The belt B on which the cover winding has been completed is removed from the pulleys 2U and 2D by the pushing means (not shown) in the cover winding machine 1 after the pulleys 2U and 2D have approached each other again.

Although one embodiment has been described above, the belt hanging device of the present invention is not limited to only the above-described example. For example, the following implementation is also possible.

A) When the pair of bars (clamp bars) holding the belt are in the closed state, the two bars do not necessarily have to be substantially parallel as shown in FIG.
It is sufficient if each bar is substantially parallel to any of the common tangents between the pulleys to be belted. As an example, a case as shown in FIG. 5 can be considered. That is, three pulleys 52L, 52M, and 52R are used to hang the belt B.
As shown in the figure, the clamp bars 61 are arranged side by side (substantially horizontally) in a long triangular shape, and when any one of them moves to apply tension to the belt B, the clamp bar 61 may be closed as follows. Should be substantially parallel to the common tangent between the pulleys 52M and 52R and between the pulleys 52L and 52R. At this time, the belt B is held between the bars 61 by being deformed so as to be more like an oval, rather than an oval.

(B) To connect the holder and the fixing member (frame) for the purpose of turning the holder without changing the direction, use pulleys 38a and 38b with teeth and a synchro belt 38c as shown in FIG. It is also possible by other than.
For example, the pulleys 38a and 38b in FIG. 3 may be replaced by gears (having the same number of teeth), and an odd number of gears (rotatably attached to the swing arm 36) may be interposed therebetween. Alternatively, the belt hanging device 70 of FIG.
, A point on the holder 73 and a point on the frame 75 may be connected by a connecting rod 78 having a certain size. FIG.
In such a case as well, when the swing arm 76 turns around the base 76a, the holder 73 having the clamp bar 71 rotates around the support shaft 77 in the opposite direction by the same angle as the turning angle of the arm 76. , Keep the overall orientation unchanged.

(C) Since the apparatus of the present invention holds the belt with a pair of rods instead of hanging it, the pulley to be hung may be arranged in a horizontal direction as shown in FIG. In addition, in FIG. 5, the direction of the axis of the pulley is related to the direction of the rod (arm 61) regardless of whether it is horizontal or vertical (upward / downward). The belt can be reliably hung between the pulleys. Also, the turning surface of the swing arm is not limited to be horizontal as in the examples of FIGS. 1 to 4, so that the belt can be transported to the pulley while changing the height. This refers to, for example, a case where the turning surface of the swing arm is vertical in the example of FIG.

D) Needless to say, the purpose of hanging the belt around the pulley is not limited to winding the cover around the belt. The apparatus of the present invention is widely useful when belts must be looped many times one after another between the same pulleys during various manufacturing processes, inspection processes, or use stages.

[0042]

According to the belt hanging device of the present invention, 1) regardless of the arrangement of the pulleys (the arrangement of the plurality of pulleys and the direction of the axis thereof), the transmission belt can be reliably and accurately reached to an optimum position around the pulley. It can be carried, and 2) even a transmission belt with a shorter circumference than the pulley diameter can be automatically hooked on the pulley.

According to the device of the second aspect, 3) the moving mechanism can be configured relatively easily, and 4) related equipment can be efficiently and compactly arranged.

[Brief description of the drawings]

FIG. 1 shows a belt hanging device 30 according to an embodiment of the present invention.
It is a front view showing the cover winding machine 1 including the whole.

FIG. 2 is a front view showing a part of the belt hanging device 30.

FIG. 3 is a side view of the belt hanging device 30 and the belt supply conveyor 40, and is a view taken along the line III-III in FIG.

FIG. 4 is a plan view of the belt hanging device 30 in FIG.
It is an IV-IV arrow line view.

FIG. 5 is an explanatory view showing a part of a belt hanging device according to another embodiment together with a pulley and the like.

FIG. 6 shows a belt hanging device 70 as still another embodiment.
FIG.

[Explanation of symbols]

 B Belt 1 Cover winding machine 2U ・ 2D ・ 52L ・ 52M ・ 52R Pulley 30 ・ 70 Belt hanging device 31 ・ 61 ・ 71 Clamp bar (bar) 32 Opening / closing mechanism 33 ・ 73 Holder 34 ・ 74 Moving mechanism 35 ・ 75 Frame ( 36 ・ 76 Swing arm 37 ・ 77 Support shaft

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-48-42814 (JP, A) JP-A-53-93251 (JP, A) JP-A-2-72545 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) F16H ⁷ /00-7/24 B25J 15/00-15/12 B29C 67/00-67/08 B29C 69/00-69/02 B29C 73/00-73 / 34 B29D 1/00-7/01 B29D 11/00-29/10 B29D 31/00-31/02

Claims (2)

(57) [Claims] 1. A device for hanging a power transmission belt between a plurality of pulleys whose mutual positional relationship is variable from an approaching state, comprising: a) a pair of rods having grooves inside the belt in a longitudinal direction thereof. B) an opening and closing mechanism that opens and closes the pair of bars between a position near and substantially parallel to the common tangent of the pulleys in the approaching state and a position having a greater distance between them, c) opening and closing with the bars. A belt mounting device, comprising: a holding device having a mechanism attached thereto; and d) a moving mechanism for moving the holding device from a belt receiving position to a position outside the pulley. 2. As the moving mechanism, a swing arm is provided to be rotatable with respect to a fixed member, and the holder is rotatably attached to a tip end thereof via a support shaft perpendicular to a turning surface of the arm. The belt hanging device according to claim 1, wherein the fixing member and the holding member are connected so that the holding member rotates in the opposite direction by the same angle as the turning angle of the arm.