Page 257 - Robot Builders Source Book - Gordon McComb

7.5 Feeding of Parts from Bins 245

off wheel 4 rotates in the direction opposite to that of the parts movement. When the
knife moves down it is immersed in the supply of blanks. In moving upward it catches
some of them and, at the upper position of the knife, these blanks fall into the slot.
Those that are successful in becoming oriented correctly will proceed in the slot under
the shut-off wheel. The others will be resumed by this wheel back into the bulk for a
new attempt.
The sliding time of an item along the slot in both the latter feeders can be estimated
as shown in Chapter 3, Section 3.1. To provide the required productivity, the length L
of the sector or the knife usually has the following relation to the blank's length I:

Here / is the length of the blank in the direction of sliding when it is properly oriented.
The feeding rate of these devices is limited by the acceleration of the knife or sector
as it reaches its upper position. Obviously, this acceleration a 0 must be smaller than g;
otherwise the blanks will jump out of the slot or lose their orientation. It is easy to esti-
mate the value of the acceleration of the knife or sector. Let us describe the displace-
ments of the knife by the following expression:

Thus, the acceleration a here has the form

and the maximum value of the acceleration a^ has the value

We must ensure that

Here, s 0 is the amplitude of the knife or sector (at the point farthest from the axis of
rotation), and (o is the frequency of oscillation in rad/sec—or in rpm we have

These two feeders are examples of devices that issue parts in portions. The number
of blanks fed per unit time is a statistical average and can be estimated experimentally
to determine the productivity of the machine that the feeder serves. To avoid interrup-
tion of processing due to lack of blanks, the outlet tray should be long enough to hold
about 25-30 blanks, to compensate for statistical deviation in the number of parts fed.
The third kind of feeding that provides a continuous flow of parts is vibrofeeding.
We have already described the phenomenon of vibrotransportation in qualitative terms
in Chapter 6, Section 6.4. A typical medium-sized vibrofeeder is illustrated in Figure
7.24. The device consists of bowl 1, whose internal surface is spirally grooved. The bowl
is fastened to platform 2, which is supported by three slanted elastic rods 3. The rods
are fastened to the platform and to base 4 by shoes 5 and 6, so that the projection of
the rods on the horizontal plane is perpendicular to the bowl's radius. The platform is
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