A third type of rapier has recently come into use . Like the
rig i d rapier this has lateral rigidity, but consists of two or three
'telescopic' components. One component is connected directly to the rapier
drive, and its weft-way position determines that of the second component, by
means of a mechanism such as, the rapier thus becomes fully extended when'
inserted in to the shed, and the components telescope together when it is
withdrawn.
Rapier
Mounting
The form of slay motion used on a rapier loom is affected by
where the rapiers are mounted. Thus, the warp-way position of the rapier,
relative to the fell, has to be such that the shed formed with the given heald
motion is big enough for them. In addition, it is essential that the rapier be
kept out of the way of the reed, even though a large part of the cycle
(typically about two thirds) is normally used for weft insertion on rapier
looms. Two mounting arrangements have to be distinguished, In the first, the
rapier are mounted on the slay and so share is warp way movement. This means
there is no question of collision between reed and rapier, and the rapier can
be guided within the working width. The slay motion can be continuous, and the slay
can have a simple crank drive. The slay can have a simple crank drive, the slay
mass is, however, increased by having to carry the. Rapier, and the
rapier-driving mechanism has to be one able to transmit motion from a fixed
driving shaft to the moving slay.
The alternative arrangement is to mount the rapier in a
fixed location on the loom frame, which simplifies the problem of transmitting
motion to them. However, with a fixed mounting rapier guidance cannot be
provided by a continuously moving slay, either inside the shed or at its
boundaries. Moreover, a continuously moving reed would have to move much
further away from the fell than the rapier. With rapiers mounted on the loom
frame, therefore, the sley is normally cam driven and dwells virtually
throughout the rapiers' motion in the reed path.
Nevertheless, in a few cases a continuously moving
crank-actuated sley is used in conjunction with rapiers which are mounted on
the loom frame. The rapiers may enter the shed nearer the fell than is usual
and the sley moves back well beyond the rapier path. If the rapiers are in the
shed for the usual fraction of the cycle, the distance from fell to rapier path
has to be substantially less than the range of sley motion, and reducing the
fell to rapier distance helps to keep this range down to an acceptable level. A
smell shed size at the point of rapier entry is a disadvantage with warps
liable to fail to form a clear shed. However. Such looms have established
themselves and combine avoidance of the expense of a cam-driven sley with a
simplification of the problem of actuating the rapiers.
In the former case the rapiers have to move further out
beyond the selvedges than is necessary for weft insertion, to reconcile their
continuous motion with the need to keep them clear of the working width until
the weft-insertion stage of the cycle recurs. This has the disadvantage that
the rapier reaches the point at which the weft is to be picked up having already
attained a substantial fraction of its maximum velocity. On being picked up by
such a rapier the weft velocity picked up by such rapier the weft velocity is
abruptly increased from zero to a high value. Against this, the rapier drive
can be a simple robust and relatively inexpensive crank-actuated mechanism.
A rapier displacement timing curve for a rapier whose path
length is confined to that needed for weft insertion. This displacement has
therefore to be confined to the appropriate part of the loom cycle too, and
such motion is readily obtained from a cam actuated mechanism. During rapier
displacement the forms of the two curves in Fig. 4 are the same, and it is
clear that the velocity at which the weft is picked up is lower for the
intermittent motion. the pickup velocity may still be appreciable though, as
rapier velocity can increase very rapidly near the beginning of the
displacement. During a Sino soidal displacement for example, a rapier would
reach 0.4 of its maximum velocity within the first 5 percent of its range of
motion.
Continuity
of Rapier Motion
A distinctive feature of most rapier looms is that the
weft'is attached to the insertion element, the rapier in this case, at a point
near the entrance to the shed, rather than at the point from which it begins
its motion - as on the Sulzer for example, or permanently -as on the shuttle
loom (this enables multicolor weft devices to be particularly simple on rapier
looms). Consequently weft insertion begins at whatever velocity has been attained
by the rapier when weft is to be picked up.