I. Motion Control Requirements for Epsilon SWB Foam Molding Machine
The image below shows the basic mechanical structure of the Epsilon SWB foam molding machine. This machine features three angular position controls: upper mold flipping, lower mold flipping, and overall flipping, as well as one vertical position control for upper mold lifting. High positioning accuracy is required for all these functions. The upper mold alone weighs up to half a ton when fully loaded.
Electric drives must achieve and meet the following requirements:
1. The foam molding machine has a symmetrical mechanical structure. The three basic actions—upper mold lifting, lower mold flipping, and overall flipping—are all driven simultaneously by two motors on both sides. The motors and reduction gears are identical in model and specifications. Therefore, ensuring that the output speed and torque of the two rigidly connected motors remain consistent is one of the challenges that the electrical drive system needs to address.If synchronous servo motors are used, this would be a very difficult control requirement. A feasible solution is to have one synchronous servo motor act as the master, operating in speed (position) mode; and the other synchronous servo motor act as the auxiliary, operating in torque mode, with its torque setpoint being the output torque value of the master servo motor.
The Danfoss FC302 driver can drive two asynchronous servo motors simultaneously. When performing motor adaptive operation, simply set the motor power and motor current to the sum of the two asynchronous servo motors.
2. Mechanical brake control
The upper mold is very heavy. If the drive and mechanical brake do not work well together during startup, it is easy to slip downwards or surge upwards.
The Danfoss FC302 drive incorporates a dedicated mechanical brake control output for lifting equipment. The timing diagram above illustrates its operation. Initially, the motor operates in torque output mode. As the mechanical brake gradually releases, the motor control mode smoothly transitions from torque control to speed control. During this transition, the PID controller for speed control can be enhanced, further improving the drive's load response capability.
3. The lower mold flipping and overall flipping are achieved through a crank mechanism; therefore, the actual mechanical angle and the motor angular displacement have a non-linear relationship.
This needs to be solved by the internal calculations of the motion controller or by using lookup table interpolation.
II. Programming and definition of high-speed bus communication interface for motion control :
Fieldbus communication control transmits process data of a predetermined word length between the master and slave stations. The Danfoss motion controller operates as a remote servo control workstation within the fieldbus network. The execution of control commands and feedback of actual position and status are all achieved through process data interaction. To facilitate integration with other host systems, and referencing the control methods of Siemens FM series motion control modules, combined with the control characteristics of the fieldbus, the following process data is defined:
| PCD1 | PCD2 | PCD3 | PCD4 | |
| Write | control word | Speed given | Location given | Torque setpoint |
| Read aloud | status word | Current actual speed | Current actual location | Current actual torque |
| Bit | bit = 0 | bit = 1 |
| 0 | Free operation | Servo Lock |
| 1 | Forward | Reversal |
| 2 | Inching | |
| 3 | Speed control mode | |
| 4 | Torque control mode | |
| 5 | Relative positioning control mode | |
| 6 | Absolute positioning control mode | |
| 7 | Return to zero | |
| 8 | Fault Reset | |
| 9 | Clear the action completion marker | |
| 10-15 | reserve |
| Bit | bit = 0 | bit = 1 |
| 0 | No forward rotation limit signal | Forward limit signal action |
| 1 | No reverse limit signal | Reverse limit signal action |
| 2 | Mechanical brake clamping | Mechanical brake release |
| 3 | During exercise | Action completed |
| 4 | Drive system is normal | Drive system alarm |
| 5 | Motion controller ready | |
| 6 | Return to zero position complete | |
| 7-15 | reserve |
III. Introduction to Danfoss Motion Controllers :
Programming methods for Danfoss motion controllers
Danfoss motion controllers use the Aposs motion control language developed by Danfoss, whose programming style mimics the C language and provides a variety of convenient commands. Its interface is shown in the following figure:
Danfoss motion controllers provide the following basic functions: 1. Input/output logic control; 2. Synchronization control, electronic cam; 3. Positioning control; 4. Interrupt functions, such as time interrupt, I/O interrupt, etc.; 5. Basic mathematical and logical operation functions; ... High-speed communication protocols supported by Danfoss motion controllers: Profibus, CANopen, DeviceNet, Interbus, LonWorks, Industrial Ethernet ... Danfoss motion controller program example (partial): //HOME MODE 1 IF (step==16) THEN homevel = GET HOME_VEL IF (home_done==0) THEN servo_on = 1 IF (svon_dlyt.2==1) THEN IF (homevel>0 AND ls_fwd==0) or (homevel<0 AND ls_rev==0) THEN IF (home_dog==1) THEN CSTOP //CVEL 0 //CSTART step = 17 ELSE ACC 50 CVEL homevel CSTART ENDIF ELSE CSTOP //CVEL 0 //CSTART IF (home_dog==1) THEN step = 17 ELSE step = 18 ENDIF ENDIF ELSE CSTOP //CVEL 0 //CSTART ENDIF ELSE CSTOP //CVEL 0 //CSTART step = 10 ENDIF ENDIFIV. Programming methods for the main control PLC:
The subroutines for motion control in the host computer can be programmed according to the following logic block diagram:
V. Usage Effect :The system's actual operation is highly satisfactory, with fast and stable response, fully meeting the control technology requirements. The general-purpose Danfoss remote controller effectively replaces the dedicated PLC motion control module. The excellent performance of the FC302 ensures positioning accuracy. The clear and concise definitions of custom communication process data and control words make host control program development much easier. VI. Conclusion :
Programming a Siemens PLC with a Siemens position control module is a challenging and complex task. However, by directly controlling a Danfoss motion controller using the PROFIBUS field communication bus, and delegating the complex programming functions to a remote servo workstation for distributed processing, not only can system costs be saved, but the overall machine development speed can also be greatly improved. This approach is worth promoting in the field of automation control. References :
[1] FC300 Programming Guide. MG.33.M4.41. Danfoss A/S. 2008
[2] User Manual for Motion Controller MCO305. MG.33.K2.02. Danfoss A/S. 2007
[2] User Manual for Motion Controller MCO305. MG.33.K2.02. Danfoss A/S. 2007
