2.3 Methodical instructions
2.3.1 Starting time, time of steady movement and time of electric breaking are the elements of the loading diagram. For calculation of starting time and breaking during linear mechanical characteristic of the motor and Мс=const formulas [1, с.363-377; 2, с.219] can be used.
Acceleration time at every starting stage for the cart:
а)
loaded
;
б)
empty
,
where Тх, Тх' are electromechanical time constants at the running correspondingly of loaded and empty cart, s;
М1 М2 – the biggest moment during start and switching moment (Fig. 1.6), Nm;
Мс1 – static moment during lifting of the loaded cart, Nm;
Мс3 – static moment during lowering of the empty cart, Nm.
2.3.2 Electromechanical time constants at running of loaded and empty cart, s:
;
where
,
is
total moment of inertia of electric drive
at
startup of loaded and empty carts correspondingly,
kgm2
(Chapter
1.1);
is
speed growth at every stage, accordingly to the moment growth
.
The
speed growth
at every stage of startup is determined from the Fig.
1.6. For
the first starting stage
;
for
the second starting stage
;
for
third
;
for
natural characteristic
.
2.3.3
Acceleration
time from the velocity
to
and
from
to
(Fig.
1.6) are
determined:
;
,
Те, Те' are electromechanical time constants for the natural characteristic during lifting of loaded cart and lowering of empty one, s.
2.3.4
Total
time of startup of loaded
and
empty
carts:
;
.
2.3.5 Time of plugging from the constant speed until complete stop for the cart
а)
loaded
;
b)
empty 
,
where
,
are
electromechanical time constants of electric drive during plugging
correspondingly at lifting of the loaded cart and lowering of the
empty cart,
s;
,
,
,
,
,
,
are
breaking moments of the motor and moments of static resistances,
Nm
(Fig.
1.6).
2.3.6 Electromechanical time constants of electric drive during plugging of the loaded and empty cart are determined by:
;
,
where
,
are
total moments of inertia of electric drive during breaking of the
loaded cart at lifting and empty cart at lowering,
kgm2
(Chapter
1);
are
determined from the Fig.
1.6.
2.3.7
For
calculation of the time of steady movement
its
necessary to define ways and velocities of steady movement.
2.3.8
Steady
movement path during lifting or descending of the cart is determined
as difference of given way
L (Table
2.1) and
ways,
which
are passed by the cart during lowering and breaking.
These
ways
are
determined
from
the construction of velocity diagrams
(Fig.2.1),
where
and
are
taken from the item 1.3.18.
Way,
which
loaded
cart
passes
during lowering and lifting,
is
equal to the square of trapezium abсd,
during
breaking is equal to the square of triangle efg.
Analogously
ways of startup and breaking during lowering of empty cart (squares
а'b'с'd' and
e'f'g')
are indentified.
2.3.9 Expressions for calculation of startup and breaking
а) during lifting of the loaded cart:
; 
;
б) during lowering of empty cart:
; 
.
2.3.10 Way and time of static movement:
а) during lifting of the loaded cart:
;
;
б) during lowering of the empty cart:
;
.
2.3.11 Duration of cart motor switching-on, %:
,
where
is
time of the cycle,
s;
are
total
time
of
startup,
fatigue movement, breaking and pauses correspondingly,
s.
2.3.12
Construction
of dependencies
and
is
shown on the Fig.
2.1. Components
of starting and breaking time are necessary to build in scale,
another
times are built without scale.
2.3.13 Equivalent moment for trapezoidal graphs:
а)
for
sections
and
also
:
;
b)
for
sections
and
also
:
,
where
for
;
for
c)
for
sections
and
also
:
.
Equivalent moments
for
rectangular
graphs
at
sections
and
also
:
.
2.3.14 For the drive of the cart intermittent cycle motor is accepted, in such a case equivalent moment must be defined for the time of actual work without taking into account pauses, by the formula:
,
where
.
Coefficient α takes into account the deterioration of cooling the motor at start-up and braking: α=0,75 is for the d.c. engine, α=0,5 is for the a.c. engine (induction motor).
2.3.15
The
resulting equivalent moment is necessary to be reduced by the formula
to
the nearest standard value of switching-on duration
ТВСТ
= 15, 25, 40,
60
%. If
Мд.ст
>Ме.ст,
the
motor
fits.
Мд.ст
is
the
moment of chosen motor at the same standard switching-on duration as
the Ме.ст,
and
it’s determined from the Tables
1.4,
1.5. For
example,
if
ТВСТ=25%,
than
,
where
is moment,
Nm;
is
capacity,
Wt;
-
angular
velocity of the motor when
ТВСТ=25%.