Hello everyone, I am Lao Wang, an engineer with over ten years of experience in the automation industry. From the chaotic days right after graduation to now being able to handle various complex projects with ease, the bittersweet experiences along the way can only be truly understood by my peers.

Today, I want to share some experiences and tips regarding multi-axis motion control in Siemens PLCs. Many engineers feel intimidated by multi-axis control, and I was no different when I first encountered it. However, after several years of practice, I found that as long as you master the core libraries and methods, you can significantly improve development efficiency and achieve a qualitative leap in system performance.

If you are working on projects that require precise coordination of multiple motors or actuators, I believe today’s sharing will provide you with plenty of inspiration.

Hardware Configuration and Environment Preparation

Essential Hardware List

Before we begin, let’s take a look at the basic hardware required for efficient multi-axis motion control:

• S7-1500 series PLC (recommended CPU 1517 or 1518 for stronger processing performance)
• ET200SP distributed I/O station (convenient for expansion and decentralized control)
• Servo drives (SINAMICS S120 or V90 series, depending on precision requirements)
• Servo motors (must match the drives, typically using the 1FK7 series)
• PROFINET network components (industrial switches, etc.)

I remember once, during a packaging line project, I underestimated the computational load and chose the 1511 CPU. As a result, I found the scan cycle unstable during the debugging phase and ultimately had to upgrade to the 1517, wasting time and costs. So, remember not to skimp on controller performance just to save money.

Software Configuration Key Points

The software environment is equally critical:

• TIA Portal V16 or higher (I am now accustomed to using V17)
• Install Technology Objects components
• Ensure the Drive Control library is installed
• It is recommended to configure SIMATIC STEP 7 Professional Edition

Tip: When creating a project, you should consider future expansion needs and reserve enough address space and hardware interfaces. I once worked on a project without considering the client’s future expansion needs, and as a result, the system required major modifications just six months after production, which was quite a headache.

The Core Principles of Multi-Axis Control

Motion Control Architecture in PLC

The multi-axis motion control of Siemens S7-1500 is implemented based on Technology Objects (TO) technology objects. This is an advanced motion control method that has several significant advantages over traditional direct programming methods:

1. Higher abstraction level, using a way that aligns more with human thinking to describe motion
2. Internally integrates complex mathematical models, eliminating the need for custom coding
3. Visual configuration interface, reducing programming difficulty
4. Supports rich motion functions such as interpolation, synchronization, cam, etc.

In my ten years of work experience, from initially using single drives for point control to now easily achieving complex systems with dozens of axes working in coordination, this progress is largely attributed to these advanced technology libraries.

Analysis of Key Functional Modules

Some of the most commonly used functional modules in Siemens multi-axis control include:

• MC_Power: Axis enable control, the foundation of all motion
• MC_Home: Axis homing function, a prerequisite for precise positioning
• MC_MoveAbsolute/MC_MoveRelative: Absolute/relative motion commands
• MC_GearIn/MC_CamIn: Electronic gear/electronic cam synchronization functions
• MC_GroupInterpolation: Multi-axis coordinated interpolation function

These function blocks do not exist independently but must be used in a certain logical combination. For example, before executing any motion command, the axis must first be enabled (MC_Power), then homed (MC_Home), and only then can the specific motion commands be executed.

Code Implementation and Technical Details

Basic Motion Control Example

Below is a simple example of dual-axis coordinated motion control:

// Axis enable
"MC_Power_1"(Axis:= "TO_Axis_1",
             Enable:= "AxisEnable",
             Status=> "AxisReady",
             Error=> "AxisError");

"MC_Power_2"(Axis:= "TO_Axis_2",
             Enable:= "AxisEnable",
             Status=> "AxisReady",
             Error=> "AxisError");

// Axis homing
IF "StartHoming" AND "AxisReady" THEN
    "MC_Home_1"(Axis:= "TO_Axis_1",
                Execute:= TRUE,
                Position:= 0.0,
                Mode:= 3);
    
    "MC_Home_2"(Axis:= "TO_Axis_2",
                Execute:= TRUE,
                Position:= 0.0,
                Mode:= 3);
END_IF;

// Axis synchronous motion
IF "StartSyncMove" AND "HomingDone" THEN
    "MC_GearIn_1"(Master:= "TO_Axis_1",
                  Slave:= "TO_Axis_2",
                  Execute:= TRUE,
                  RatioNumerator:= 2,
                  RatioDenominator:= 1);
    
    "MC_MoveAbsolute_1"(Axis:= "TO_Axis_1",
                        Execute:= TRUE,
                        Position:= 1000.0,
                        Velocity:= 200.0,
                        Acceleration:= 100.0,
                        Deceleration:= 100.0);
END_IF;

Practical Advice: For multi-axis systems, I prefer to create a unified axis management function block that consolidates the status management and error handling of all axes, which can greatly simplify the logic of the main program.

Advanced Synchronization Control Techniques

Multi-axis synchronization is a core requirement for many high-precision applications. Siemens provides several advanced synchronization methods:

1. Electronic Gear (MC_GearIn): Suitable for fixed ratio following motion
2. Electronic Cam (MC_CamIn): Suitable for nonlinear, complex trajectory synchronization
3. Multi-Axis Interpolation: Suitable for spatial trajectory control, such as robots, CNC machines, etc.

I encountered a tricky problem when applying the electronic cam function on a printing device: the synchronization accuracy was insufficient during high-speed operation. After repeated testing, I found that the resolution of the cam table was not high enough. After increasing the original 100 points to 500 points, the accuracy issue was resolved.

Tip Sharing: In high-speed applications, the number of points in the cam table should not be excessively high; it should be set reasonably based on actual speed, acceleration, and system processing capability. Too many points may lead to excessive CPU load, which in turn reduces control accuracy.

Function Expansion and System Optimization

Efficient Data Management Methods

In multi-axis systems, data management is crucial. I have found the following methods particularly effective:

1. Use UDT (User Defined Data Types): Create a unified format data structure for each axis for easier management
2. Centralized Parameter Management: Create dedicated parameter DB blocks for easy online adjustments and backups
3. Status Monitoring: Design a well-structured status monitoring system to quickly locate issues

// Axis data structure example
TYPE "AxisDataType"
VERSION : 0.1
   STRUCT
      Enable : Bool;   // Enable signal
      Reset : Bool;    // Reset signal
      Start : Bool;    // Start signal
      Stop : Bool;     // Stop signal
      Jog_Positive : Bool;  // Positive jog
      Jog_Negative : Bool;  // Negative jog
      TargetPosition : Real;  // Target position
      ActualPosition : Real;  // Actual position
      ActualVelocity : Real;  // Actual velocity
      Error : Bool;    // Error flag
      ErrorID : Word;  // Error code
   END_STRUCT;
END_TYPE

Performance Optimization Tips

Multi-axis systems often face performance challenges. Here are some optimization suggestions I have summarized:

1. Set Scan Cycles Reasonably: Motion control tasks usually require a separate scan cycle, typically shorter than the main program cycle
2. Optimize Communication Load: Minimize unnecessary data exchanges, especially on the PROFINET network
3. Use Interrupt Techniques: For time-critical tasks, hardware interrupts or clock interrupts can be used
4. Distributed Processing: Offload some computational tasks to the drive level to reduce the PLC burden

I remember once, when our system was running 16 axes simultaneously, we encountered a strange delay issue. After in-depth analysis, we found that it was due to excessive PROFINET communication load. Changing the original linear topology to a star topology immediately resolved the issue.

Case Study Analysis

Multi-Axis Collaborative Applications in the Packaging Industry

In a high-speed food packaging line project, we used S7-1517 to control 12 servo axes working in coordination, achieving the following functions:

1. Feed synchronization (2 axes)
2. Cross-sealing cutting (4 axes)
3. Longitudinal sealing and heat pressing (2 axes)
4. Finished product conveyor sorting (4 axes)

The system can reach up to 120 packages per minute, with positioning accuracy of ±0.1mm. The key point was using MC_CamIn to achieve precise synchronization between workstations, and by modifying the cam curve online, we enabled quick switching between different packaging specifications.

On-Site Experience: Debugging multi-axis systems is labor-intensive; we spent a full two weeks fine-tuning parameters. The key is to start slow, gradually increase speed, and ensure system stability at each stage before moving to the next.

Applications in Printing Equipment

Another case is the retrofit of a roll paper printing machine, changing from mechanical drive to electronic cam control. This system used 8 servo axes:

1. Main axis (defines main speed)
2. Paper feeding axis (synchronized with the main axis but requires tension control)
3. Four printing units (each unit needs to be precisely synchronized with the main axis)
4. Winding axis (requires tension control)

By using Siemens Technology Objects, we not only achieved precise synchronization of all axes but also added electronic phase adjustment functionality, allowing operators to directly adjust the printing position on the touchscreen without stopping for mechanical adjustments, resulting in a productivity increase of about 300%.

Debugging Methods and Tips Sharing

Step-by-Step Debugging Strategy

The biggest taboo in multi-axis system debugging is to try to achieve everything in one go. I always follow these steps:

1. Single Axis Debugging: Ensure each axis operates normally on its own first
2. Dual Axis Synchronization: Test the basic master-slave relationship
3. Multi-Axis Low-Speed Testing: Verify overall system coordination at low speeds
4. Gradual Speed Increase: Confirm stability at each speed point
5. Boundary Testing: Test limit positions, limit speeds, etc.

Important Reminder: Always remember safety first! Be sure to set up software limits, hardware limits, and emergency stop functions before conducting any dynamic tests.

Common Problem Solutions

Here are some common problems I have encountered and their solutions:

1. Excessive Following Error:

• Check servo parameters, especially gain settings
• Consider increasing cam table resolution
• Check for mechanical play in the system

System Instability:

• Check if the PLC scan cycle is stable
• Check network load conditions
• Consider reducing acceleration parameters

Position Drift:

• Check encoder signal quality
• Consider periodic automatic homing
• Check the mechanical transmission parts

I once struggled for several days with a position drift issue in a system, only to find out that it was caused by mechanical vibrations leading to loose encoder wiring. This taught me that you should not only focus on software and parameters; sometimes the problem may lie in the most basic hardware connections.

Summary and Insights

Through the multi-axis motion control library of Siemens PLC, we can easily accomplish tasks that previously required complex programming. From my personal experience, mastering these technologies has reduced project development cycles by an average of 60%, improved system performance by over 200%, and decreased failure rates by 80%. These numbers translate into tangible benefits.

As an automation engineer, continuously learning new technologies and enhancing my professional skills is crucial. As an experienced mentor once told me when I first entered the industry: “In this field, if you are not progressing, you are regressing.”

I hope today’s sharing is helpful to everyone. If you have any questions or experiences to share regarding multi-axis control, feel free to leave a comment for discussion. After all, our greatest motivation for growth is learning from each other and progressing together.