In many industries, shaftless drive technology has replaced the old mechanical drive systems. Instead of using mechanical gearing to force one axis on a machine to follow another one, servos are used. The servo technology reduces many of the flaws of a large mechanical gearing system as well as provides a lot of flexibility. This technology is in heavy use in industries such as the automotive, packaging, and printing.
Using the shaftless drive technology requires the use of a motion controller to command the system. Siemens Industry and Automation’s motion control platform, SiMotion, is a powerful and flexible platform that can be used for such a purpose. The SiMotion software package allows the programmer to configure all of the drives and axes with great flexibility and detail and gives the capability to program in three different languages: text-based, ladder or function block diagram (FBD), and in a motion chart.
A typical approach to programming a shaftless drive solution would be to do any math required in the text-based portion, any peripheral I/O control and basic sequence logic would be done in ladder, and all of the motion commands to control the axes/drives would be programmed in the Motion Charts. The Motion Chart section would contain all of the individual motion commands to control the axes from enabling and disabling, to moving to a position, to gearing.
Since most of the shaftless drive solutions follow the same control strategy, Siemens has created the “SiMotion Shaftless Drive Standard”. This Standard outlines a programming structure and contains a library of functions that work well to control such solutions. The basic ideas contained in this strategy are outlined below:
- All of the tasks such as basic logic processing are done in the cyclical background tasks and all of the motion tasks are done in the a-cyclical Motion Tasks.
- The standard supplies a pre-written Motion Task for each axis specific to the tasks of line-shaft replacement system.
- Control of each axis is performed through a standard mode interface.
- A set of typical axis modes are defined and the motion tasks are almost entirely performed simply by assigning a mode to the axis.
- The interface parameters affect the axis behavior in each mode.
In a recent project, I implemented the SiMotion Shaftless Drive Standard for a printing application- a rotary cutter positioned at the end of a printing press. This application contains the basic components that allow for easy implementation of the standard. There are three rotary axes on the rotary cutter that are geared during operation to follow an encoder on the press. A “knife setup” routine allows the operator to step through several configurable positions on the knife axis. The implementation of the Shaftless Standard contains the following components:
- A Virtual Master axis follows the press encoder.
- The program contains three real following axes which follow the Virtual Master.
- Each axes has its own Motion Task consisting of a call to the Standard’s axis function block.
Using the Shaftless Standard gives several advantages:
- In order to gear each of the real axes to the virtual master, we simply need to set the axes in “Gear Mode” and the Standard takes care of the individual motion commands.
- The knife setup routine requires that we put the knife axis in “positioning mode”. Then the program just changes the position set point for each new position, and the axis moves to that position.
- Since we use a setup that is a standard recognized by Siemens, the system is easily supported by Siemens world-wide network of application engineers.
- Once a programmer is comfortable designing systems following the Shaftless Standard, program creation and debug times are shortened.
The SiMotion Shaftless Drive Standard is available to qualified end-users and Automation Solution Providers, such as DMC through your local Siemens Application Engineer.
You can read more about the Rotary Cutter project in our case studies.