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APM Screw

Screw gears are used for еру transformation of еру rotational movement of the screw to the transactional movement of the nut. They are widely applied in the machine tool industry, aircraft industry, robototechnics and many other areas of the modern mechanical engineering. Meanwhile, the existing methods of screw gear calculation collide with number of the serious problems.

Gear types in APM Screw

APM Screw is a comprehensive software for calculation of screw gears. It allows you to perform a complex analysis of the screw gears, compute its main performances, and select the optimum parameters of gear elements.

The most widely used types of the screw gear

In the APM Screw you can calculate the most widely used types of screw gears. For the ball screw gears two subtypes can be calculated — with one nut and with two half nuts (the latter allows the preload use).

APM Screw main window and calculation progress bar

The theory of the non-ideal contact—the basis of the APM Screw.

The main advantage of the APM Screw is that it allows considering the influence of manufacturing errors on the screw gear performances. It becomes possible due to the new theory of non-ideal contact, developed in the Research and Software Development Center APM Ltd. This theory is applicable to the wide range of machine elements, such as bearings, screw gears, plain joints, rolling contact guides, etc. It allows you to get reliable values of the contact displacements, stiffness, stresses and all parameters that are depended on the formers, such as longevity, moment of friction, loss of power, etc.

With the APM Screw the following parameters can be calculated:

   With the APM Screw the following parameters can be calculated:

  • displacements (stiffness)
  • longevity
  • moment of friction
  • maximum contact stress
  • loss of power
  • heat release
  • forces acting on the rolling bodies
  • efficiency
  • positioning errors

Simulation instead of the single parameter’s calculation

Due to the randomly distributed irregularities of the contacting surfaces, the interaction of the screw, nut and rolling bodies has the probabilistic nature and can be adequately described only in the statistical sense. With the APM Screw you get the complete and exhaustive picture of processes that take place when a screw gear works. Virtually Screw allows simulating the behavior of the screw gear at the conditions that you have specified. To provide such opportunity reasonably large series of the parameter values are computed, showing how these parameters are changing. When using these data, you can determine features of the distribution, maximum deviations, fields of dispersion, etc.

Dialog box results of calculation
 

Displacements and stiffness—the core of the system

Stiffness and contact displacements describe how the elements of the mechanical device interact under loading. If you know the stiffness, you can get the reliable values of many other parameters.
In the APM Screw the list of 100 nut center positions is computed. Depending on the screw gear type a displacement can have up to three components — axial, radial, angular. When using them it is possible to determine the axial, radial and angular stiffness and compliance with the gear. The list of the nut center positions is the core of the APM Screw. For each position values of the moment of friction and the loss of power are computed together with the forces acting on the rolling bodies.

Forces acting on the rolling bodies

Stiffness and contact displace-ments describe how the elements of the mechanical device interact under loading. If you know the stiffness, you can get the reli-able values of many other parameters.

Friction moment, loss of power and forces acting on the rolling bodies are calculated for each considered center position.

Result representation

The results are represented in different ways:

  • as a table supplemented with the statistical parameters;
  • as a histogram
  • as a graph
  • as an animation

When using the appropriate forms of the presentation you get an exhaustive characteristic of the screw gear movement.

Axial displacement histogram

Graph of displacement errors

Forces acting on the rolling bodies

During the rotation of screw gear its rolling bodies (or satellites in the case of the planetary gear) are subject to the normal forces action applied from the screw and nut and depending on the geometry, accuracy, external load, etc.     

Existing methods overidealize the problem producing oversimplified solution. The new approach was developed. It gives a more real picture. In the APM Screw the forces acting on the rolling bodies are computed for the each member of the large series of the nut center positions determined during the gear displacements calculation. As a result you are given a possibility to trace how these forces change in time.

Forces acting on the rolling bodies are presented in two ways::

  • as an epure
  • as a graph

Friction in the screw gear

In the APM Screw you can determine the following parameters characterizing the action of the frictional forces:

  • moment of friction
  • loss of power
  • heat release
  • efficiency

 

For the moment of friction and loss of power a list of 100 values is calculated, so you can determine the features of the distribution of these parameters. The results can be presented either as tables, as histograms or as graphs.

The heat release is an integral parameter characterizing the amount of the heat released in the gear due to the friction during a time period of one hour.

An arbitrary loading conditions including the preload

   Calculations in the APM Screw can be made for any combination of axial and radial forces, overturning the moment and the preload allowed for a screw gear of the given type. External loads by longivity calculation can be considerd to be variable in time. There is a special graph editor for that purpose.