On the motor power, torque and inertia2016-10-28
For a specific application, when selecting a motor, consider a series of data such as speed, torque, load inertia, etc., so that the selected motor to meet the requirements without causing waste, costly .
Rated power P, rated speed N and rated torque T
There is such a formula, the speed N (rpm) can be calculated from the power P (W) and torque T (N · m):
The formula shows that the same power, torque and speed are inversely proportional to the use of gearbox to enlarge the output torque, while reducing the speed.
From the point of view of doing the work, the derivation process is as follows:
among them:
F for the motor output force, in N (cattle);
R is the arm, the unit is m (m);
N is the motor speed, the unit is rpm (r / min).
We know that the definition of torque T is force (F) multiplied by the arm (r), namely:
T = F · r
Therefore, the above equation can be obtained:
P = (2π / 60) · T · N = 0.105 · T · N
among them:
P is the motor rated power, the unit is W;
T is the motor rated torque, the unit is N · m;
N is the rated motor speed in rpm.
Inertia and moment
The motor has a small inertia, the inertia and the inertia of the motor, the same power, the greater the motor inertia J, the greater the motor output torque, but the lower the speed. Therefore, the small inertia motor has the advantage of fast response speed, of course, this premise is that the drag load inertia can not be too large.
The unit of inertia is Kgm2, which is defined as follows: From the energy perspective:
Since the mass and radius in the equation are constant for a given object, they are extracted and become the inertia J:
J = mr²
From the perspective of doing work, motor output torque work W:
Ideally, the motor torque to do all the work into function, too:
W = E
Therefore:
which is:
among them:
T is the torque, the unit is N · m;
J is the total inertia, the unit is Kgm2;
Β is the angular acceleration in rad / s2;
From the formula can be obtained, inertia and acceleration are directly related to, in a particular application, if the load inertia is constant and known, can be calculated from the required acceleration of the motor output torque, as one of the parameters of motor selection.
to sum up
The motor rated power, rated torque, rated speed, moment of inertia, if the installation of a motor speed reducer, the motor rated power constant, rated torque increases, the rated speed decreases, the inertia increases.
Therefore, to select a motor for a system, it is necessary to know the load inertia of the system, the required maximum speed, the required maximum acceleration / deceleration time, system voltage, etc., to calculate a series of motor parameters, and then motor selection, Satisfying system requirements does not constitute waste.
