[analysis] engine-load inertia report: how to improve it?

[cad3d]

[ARTICOLO DUPLICATO DALLA HOMEPAGE]​

in the design phase of machines in which rotating drives are present, it is not rare to have to assess the effects of inertial imbalance of the system. a golden rule for the sizing of the rotating system previews to couple a motor system with a load in order to have a moment of inertia of the engine greater than 10 times than that of the load.

in this article we will see how excessive inertial imbalance worsens the dynamic features of the application and what to do to improve them.
rigid or elastic systems

with infinite k resonance frequency is infinite, however infinitely rigid systems do not exist, even the more rigid material has a finished young module, but in the case of extreme dynamics, for which high precision is required, it is necessary to have a system as rigid as possible. If on the one hand the young module of the material represents an invaluable physical limit, on the other, it is possible to work on the geometry of the component to obtain a rigidity of the motor-load connection adequate to the response required by the system.

from the chart you can see the behavior of a “rigid” system compared to a “elastic” given a bike profile:
rigid system

elastic system

reducer foreplay and defectsthe introduction of a reducer has the advantage of containing the apparent inertia of the load. In fact the presence of a reducer decreases the dynamic load perceived by the motor due to the inertial response of the load to the variation of motion. This reduction is proportional to the square of the transmission ratio of the reducer:

what is exposed entails a single disadvantage: increased energy consumption during the motorcycle transients.

which results in this graph:

the reducer has other disadvantages:

• a proper torsion rigidity that weighs on the rigidity of the transmission. in other words the torsion rigidity of the transmission will be lower than that of the transmission without reducing
• among the organs of the reducer there are games that produce relative rotations of the axes, regardless of elastic deformation. even in the case of reduced playbacks it is not possible to cancel the game between the parts in relative motion

these aspects produce two harmful effects on the transmission of motion:

1. additional vibrations are introduced
2. global transmission stiffness decreases and system resonance frequencies lower

Conclusionsin this short document a brief reflection on the aspects of inertial imbalance of rotating systems is presented. many aspects are not considered, some of which have an important role on the dynamics of the system, for example: the logic of control in retroaction and the law of motion in phase of acceleration (it is known that the values of jerk in cam profiles should be very low to have an optimal control).

However, a solution to the question was raised: “Is it right to have an imbalance of 1:10? ”

as demonstrated the answer is not trivial and univocal. much depends on the system response time, the more the response time is low (fast system in response) the more the system itself is accurate. below are examples of response for two systems having different response times when operated by the same motion law.

in this particular case considering acceptable 24 ms response time representing about 10% of the cycle you can accept an inertial imbalance of 1:35 for elastic systems and 1:140 for rigid systems.

author: chierici pierluigi, asotech srl

 

[davide_pontini]

hello to all are the ingenuity, planner of automatic machines.
the premise of the whole article is wrong!
a golden rule for the sizing of the rotating system previews to couple a motor system with a load so that you have a moment of inertia of the engine greater than 10 times than that of the load.the engine inertia must be 10 times smaller than that of the reduced load to the motor shaft, in the company we size everything so.
cad3d, do you give me the magazine?

 

[Archimed&]

hello to all are the ingenuity, planner of automatic machines.
the premise of the whole article is wrong!
a golden rule for the sizing of the rotating system previews to couple a motor system with a load so that you have a moment of inertia of the engine greater than 10 times than that of the load.the engine inertia must be 10 times smaller than that of the reduced load to the motor shaft, in the company we size everything so.
cad3d, do you give me the magazine?

Motori passo passo inerzia rotorica rotor inerzia

description

www.motorepassopasso.com

 

[Chris_BRB]

Good morning to all,
depends on the type of application not? the more the system must respond effectively in terms of positioning accuracy and response speed the lower the inertia ratio. in machine tools for example must be between 1 and 3 from fanuc catalog.

 

[davide_pontini]

the observation was about the fact that it was dimensioned all with an inertia of the motor greater than the load rather than less. of what depends on the application, but must always be at least lower

 

[Archimed&]

the observation was about the fact that it was dimensioned all with an inertia of the motor greater than the load rather than less. of what depends on the application, but must always be at least lower

the observation was about the fact that it was dimensioned all with an inertia of the motor greater than the load rather than less. of what depends on the application, but must always be at least lower

hi I don't know you read the link, from there it seems to me to quickly understand that it gives reason to the article of cad3d. even intuitively I think that less is the inertia of the load better is

 

[Archimed&]

hi I don't know you read the link posted by me a few minutes ago, from there it seems to me to quickly understand that it gives reason to the article of cad3d. even intuitively I think that less is the inertia of the load better is

 

[davide_pontini]

in intuitive mechanics there is nothing. The less the inertia of the load the better is at the level of the engine size. then you should specify if it is a brushless, one step, etc.
in automatic machines with brushless drives the inertia of the motor cannot be compared to that of the load because they trigger phenomena of pursuit of the motor that do not solve.
my observation was that you can not indicate a golden rule in general when in fact in the case I indicated is exactly the opposite (load iner around 10 times that of the engine)