Case Studies

Position Control of a Three-Axis Gantry using an S7-1511 and V90 Servo Drives

Posted in Application Development, Siemens PLC, Specialty Machinery


DMC programmed a three-axis gantry system using an S7-1511 and four V90 servo drives. 


This program needed to be able to move the gantry between points in the system while maintaining precise speed and positioning tolerances. Two of the axes were controlled by a single drive while the third required two of the V90s to be geared together. All four drives used telegram 105, which allowed for both position and speed control.

To help interface these drives with DMCs code, technology objects were implemented. Each axis was primarily controlled by a position axis technology object with a synchronous axis technology object added in to accommodate the second VFD being used to move the Y axis.

Since the PLC was a 1500 series and not a 1500T, we were not able to absolutely gear the two Y axis VFDs to one another. DMC circumvented the potential issue by relatively gearing the two axes at a 1 to 1 ratio. Using this setup, we were able to move gantry to very precise points within the system at speeds within the end user’s requirements. If used in a system with a 1500T, DMC would have also been able to utilize Siemen’s kinematics technology object.  This would have allowed for the creation of Cam profiles and much smoother point to point movement in the system.

Another benefit to using the technology objects is that they allowed DMC to easily incorporate hardware stops to the program. In the limits configuration for the technology objects, the programmer can directly set digital inputs as end of range limits for a given axis. These limits can also be configured to be either normally open or normally closed.

By using Siemen’s built-in functionality, DMC was able to effectively meet the needs of the project and work around potential hardware limitations.

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Customer Benefits

  • Position and speed control
  • Incorporation of hardware stops