DMC programmed a machine to fill small bottles of liquid at rates up to 1,000 bottles per minute, using several coordinated axes to transfer bottles between sections of the machine. Our role was to program and commission the motion aspects of the project, as well as to update existing code to use best practices with Siemens PLCs.
DMC’s customer had an existing machine design that fills small bottles using Rockwell hardware for automation. Because their end client’s factory already had several other machines that utilize Siemens hardware, they requested that the existing machine was converted to Siemens technologies. Through the use of technology objects and S-series drive controls, the client was able to improve their machine to run at an even faster rate without sacrificing precision or quality.
Two main servo axes first move the product through the machine from the inlet, then to filling, capping, and finally out of the machine. The interface between the two axes required a tight tolerance in order to avoid crushing bottles while passing them between the two axes. The axes were both controlled via technology objects, and used a velocity gearing between the two to match speeds. DMC then implemented a superimposed motion on top of the velocity gearing. This allowed the axes to correct for any small offset created during acceleration or deceleration, for better synchronization, faster start up and shutdown, and a higher top speed.
Other drives on the machine whose position were not critical were changed to Danfoss drives to control the speed, reducing the overall hardware cost. DMC created one function block to control a drive's speed and monitor its current usage, and then implemented it for each drive, reducing programming time and providing standard diagnostics and alarming.
The machine also needed to be able to detect if there were any bottles without caps so that they could be rejected before proceeding to packaging. With the machine operating at full speed, this detection needed to occur within a 60 millisecond window per bottle, which was 10 milliseconds faster than the previous version. DMC used a high-speed cyclic interrupt and a process image partition to read from the cap sensor 20 times per bottle, ensuring detection of bottles without caps with an extremely high level of accuracy.
The programming logic was written in TIA Portal V13 SP1's ladder logic editor using technology objects to control the servos. The technology objects coordinate the motion between the servos and also allow for easier monitoring and commissioning. The technology object has a slew of parameters and alarms that give the user more information, from commanded and actual positions to in-depth error codes. The trace features of the S7-1500 PLC allow the user to measure and analyze that data in a clear, graphical environment. Tracing also makes monitoring digital inputs, outputs, and program logic possible even at very high speeds.
Learn more about DMC's Siemens motion control and PLC programming services.