Bosch Rexroth Function Blocks for Safety Systems: Complete Programming Guide

Implementing Function Blocks for Safety Systems using Bosch Rexroth ctrlX WORKS / IndraWorks requires a documented design, applicable standards, and project-specific acceptance criteria. This guide organizes practical checks for code structure, diagnostics, testing, and maintenance.

The example references ctrlX CORE XM21-family terminology, but model capabilities vary. Verify the controller manual, the installed ctrlX WORKS / IndraWorks version, and any applicable machinery, process, electrical, or functional-safety requirements for the actual project.

Best practices for Safety Systems encompass multiple dimensions: proper handling of 5 sensor types, safe control of 4 different actuators, managing safety integrity level (sil) compliance, and ensuring compliance with relevant industry standards. The Function Blocks approach, when properly implemented, provides visual representation of signal flow and good for modular programming, both critical for advanced projects.

This guide presents a reviewable approach to Bosch Rexroth Function Blocks programming for Safety Systems, covering code organization, documentation, test procedures, and maintenance handoff. The sample logic is educational and must be compiled, simulated, peer-reviewed, and tested against the project's acceptance criteria before use on equipment.

Bosch Rexroth ctrlX WORKS / IndraWorks for Safety Systems

ctrlX WORKS / IndraWorks is a programming environment associated with Bosch Rexroth controller families such as ctrlX CORE XM21, ctrlX CORE XM22, ctrlX CORE XM42. This guide uses Function Blocks terminology from the supplied guide dataset, but controller capabilities and language support can change by model, firmware, software edition, and license.

Verify Before You Start:

The selected controller supports the required Function Blocks constructs

The project version matches the installed ctrlX WORKS / IndraWorks release

Required communications, motion, safety, and simulation options are licensed

Firmware and device-description files are compatible with the project

The vendor manuals used for the design match the exact hardware revision

Application Planning:

For a Safety Systems exercise, map the required inputs and outputs before writing logic. The example considers 5 sensor types, including Safety light curtains, Emergency stop buttons, Safety door switches, and 4 actuator types.

Control Equipment for Safety Systems:

Safety PLCs (fail-safe controllers)

Safety relays (configurable or fixed)

Safety I/O modules with diagnostics

Safety network protocols (PROFIsafe, CIP Safety)

Controller-family references used in this guide include:

ctrlX CORE XM21: Confirm CPU, I/O, memory, communications, and Function Blocks support in the current selection guide

ctrlX CORE XM22: Confirm CPU, I/O, memory, communications, and Function Blocks support in the current selection guide

ctrlX CORE XM42: Confirm CPU, I/O, memory, communications, and Function Blocks support in the current selection guide

IndraControl XM21: Confirm CPU, I/O, memory, communications, and Function Blocks support in the current selection guide

Hardware Selection Checklist:

Count local and remote I/O, including planned expansion

Measure the required task and communications update rates

Identify memory, data-retention, diagnostics, and cybersecurity requirements

Treat safety functions as a separate, standards-led design activity

Confirm lifecycle status, regional availability, licensing, and support

Source and Validation Note:

This page does not represent a vendor certification or a hardware acceptance test. Use current Bosch Rexroth manuals, release notes, and safety documentation as the authority for product-specific behavior. Validate adapted logic in a simulator or isolated test setup before connecting it to equipment.

Investment Considerations:

For Safety Systems projects, compare hardware, software licensing, training, engineering, test equipment, commissioning, spares, and ongoing support. Obtain current pricing and lifecycle information directly from the vendor or an authorized regional supplier.

Understanding Function Blocks for Safety Systems

Function Block Diagram (FBD) is a graphical programming language where functions and function blocks are represented as boxes connected by signal lines. Data flows from left to right through the network.

Execution Model:

Blocks execute based on data dependencies - a block executes only when all its inputs are available. Networks execute top to bottom when dependencies allow.

Core Advantages for Safety Systems:

Visual representation of signal flow: Critical for Safety Systems when handling advanced control logic

Good for modular programming: Critical for Safety Systems when handling advanced control logic

Reusable components: Critical for Safety Systems when handling advanced control logic

Excellent for process control: Critical for Safety Systems when handling advanced control logic

Good for continuous operations: Critical for Safety Systems when handling advanced control logic

Why Function Blocks Fits Safety Systems:

Safety Systems systems in Universal typically involve:

Sensors: Emergency stop buttons (Category 0 or 1 stop), Safety light curtains (Type 2 or Type 4), Safety laser scanners for zone detection

Actuators: Safety contactors (mirror contact type), Safe torque off (STO) drives, Safety brake modules

Complexity: Advanced with challenges including Achieving required safety level with practical architecture

Programming Fundamentals in Function Blocks:

StandardBlocks:
- logic: AND, OR, XOR, NOT - Boolean logic operations
- comparison: EQ, NE, LT, GT, LE, GE - Compare values
- math: ADD, SUB, MUL, DIV, MOD - Arithmetic operations

TimersCounters:
- ton: Timer On-Delay - Output turns ON after preset time
- tof: Timer Off-Delay - Output turns OFF after preset time
- tp: Pulse Timer - Output pulses for preset time

Connections:
- wires: Connect output pins to input pins to pass data
- branches: One output can connect to multiple inputs
- feedback: Outputs can feed back to inputs for state machines

Best Practices for Function Blocks:

Arrange blocks for clear left-to-right data flow

Use consistent spacing and alignment for readability

Label all inputs and outputs with meaningful names

Create custom FBs for frequently repeated logic patterns

Minimize wire crossings by careful block placement

Common Mistakes to Avoid:

Creating feedback loops without proper initialization

Connecting incompatible data types

Not considering execution order dependencies

Overcrowding networks making them hard to read

Typical Applications:

1. HVAC control: Directly applicable to Safety Systems
2. Temperature control: Related control patterns
3. Flow control: Related control patterns
4. Batch processing: Related control patterns

Understanding these fundamentals prepares you to implement effective Function Blocks solutions for Safety Systems using Bosch Rexroth ctrlX WORKS / IndraWorks.

Implementing Safety Systems with Function Blocks

Safety system control uses safety-rated PLCs and components to protect personnel and equipment from hazardous conditions. These systems implement safety functions per IEC 62443 and ISO 13849 standards with redundancy and diagnostics.

This walkthrough demonstrates practical implementation using Bosch Rexroth ctrlX WORKS / IndraWorks and Function Blocks programming.

System Requirements:

A typical Safety Systems implementation includes:

Input Devices (Sensors):
1. Emergency stop buttons (Category 0 or 1 stop): Critical for monitoring system state
2. Safety light curtains (Type 2 or Type 4): Critical for monitoring system state
3. Safety laser scanners for zone detection: Critical for monitoring system state
4. Safety interlock switches (tongue, hinged, trapped key): Critical for monitoring system state
5. Safety mats and edges: Critical for monitoring system state

Output Devices (Actuators):
1. Safety contactors (mirror contact type): Primary control output
2. Safe torque off (STO) drives: Supporting control function
3. Safety brake modules: Supporting control function
4. Lock-out valve manifolds: Supporting control function
5. Safety relay outputs: Supporting control function

Control Equipment:

Safety PLCs (fail-safe controllers)

Safety relays (configurable or fixed)

Safety I/O modules with diagnostics

Safety network protocols (PROFIsafe, CIP Safety)

Control Strategies for Safety Systems:

1. Primary Control: Safety-rated PLC programming for personnel protection, emergency stops, and safety interlocks per IEC 61508/61511.
2. Safety Interlocks: Preventing Safety integrity level (SIL) compliance
3. Error Recovery: Handling Redundancy requirements

Implementation Steps:

Step 1: Perform hazard analysis and risk assessment

In ctrlX WORKS / IndraWorks, perform hazard analysis and risk assessment.

Step 2: Determine required safety level (SIL/PL) for each function

In ctrlX WORKS / IndraWorks, determine required safety level (sil/pl) for each function.

Step 3: Select certified safety components meeting requirements

In ctrlX WORKS / IndraWorks, select certified safety components meeting requirements.

Step 4: Design safety circuit architecture per category requirements

In ctrlX WORKS / IndraWorks, design safety circuit architecture per category requirements.

Step 5: Implement safety logic in certified safety PLC/relay

In ctrlX WORKS / IndraWorks, implement safety logic in certified safety plc/relay.

Step 6: Add diagnostics and proof test provisions

In ctrlX WORKS / IndraWorks, add diagnostics and proof test provisions.

Bosch Rexroth Function Design:

Rexroth engineers lean heavily on reusable function blocks packaged as ctrlX libraries. The mapp-technology-equivalent SDK apps expose motion-profiled FBs, recipe-driven parameter handlers, and cockpit widgets as pre-built components. OEM machine builders maintain private app catalogues for their machine families, with versioned FBs that can be swapped between machine variants without rewiring upstream code. IEC 61131-3 OOP extensions (classes, interfaces, methods) are used in more advanced teams but are optional.

Common Challenges and Solutions:

1. Achieving required safety level with practical architecture

Solution: Function Blocks addresses this through Visual representation of signal flow.

2. Managing nuisance trips while maintaining safety

Solution: Function Blocks addresses this through Good for modular programming.

3. Integrating safety with production efficiency

Solution: Function Blocks addresses this through Reusable components.

4. Documenting compliance with multiple standards

Solution: Function Blocks addresses this through Excellent for process control.

Safety Considerations:

Use only certified safety components and PLCs

Implement dual-channel monitoring per category requirements

Add diagnostic coverage to detect latent faults

Design for fail-safe operation (de-energize to trip)

Provide regular proof testing of safety functions

Performance Metrics:

Task and I/O timing: Record minimum, average, and maximum values under a defined test load

Accuracy: Define an acceptable tolerance and compare it with calibrated reference measurements

Throughput: Count completed cycles over a fixed interval and record rejected or incomplete cycles

Fault response: Measure detection, safe-state, alarm, and recovery behavior for each test case

Resource use: Record memory, communications load, and diagnostic-buffer behavior

Bosch Rexroth Diagnostic Tools:

ctrlX WORKS Trace tool — multi-variable waveform logging at up to 1 ms sample rate,Data Layer Explorer — browse every runtime variable in a hierarchical tree with live values,Web-based diagnostics interface — device-level health, CPU and memory utilisation,IndraWorks MotionManager — axis commissioning, tuning plots, and envelope monitoring,ctrlX I/O Engineer — field-bus topology view with per-slave diagnostic status,Integrated Git history for project files with visual diff between versions,Wireshark integration for EtherCAT and Profinet frame capture and analysis,Linux journalctl access on ctrlX CORE for controller-side system log inspection,REST API query tools (Postman, curl) for runtime variable inspection during development,SSH access to the ctrlX controller for deep diagnostics when support escalation is required

Use the monitoring and diagnostic functions available in your ctrlX WORKS / IndraWorks version, and record the software, firmware, hardware, workload, and test procedure with every result.

Bosch Rexroth Function Blocks Example for Safety Systems

Illustrative Function Blocks example for Safety Systems using Bosch Rexroth terminology. Adapt the syntax to your ctrlX WORKS / IndraWorks release, compile it, and verify it in an isolated test environment before use on equipment.

(* Bosch Rexroth ctrlX WORKS / IndraWorks - Safety Systems Control *)
(* Reusable Function Blocks Implementation *)
(* Rexroth engineers lean heavily on reusable function blocks p *)

FUNCTION_BLOCK FB_SAFETY_SYSTEMS_Controller

VAR_INPUT
    bEnable : BOOL;                  (* Enable control *)
    bReset : BOOL;                   (* Fault reset *)
    rProcessValue : REAL;            (* Emergency stop buttons (Category 0 or 1 stop) *)
    rSetpoint : REAL := 100.0;  (* Illustrative value; replace with a reviewed requirement *)
    bEmergencyStop : BOOL;           (* Safety input *)
END_VAR

VAR_OUTPUT
    rControlOutput : REAL;           (* Safety contactors (mirror contact type) *)
    bRunning : BOOL;                 (* Process active *)
    bComplete : BOOL;                (* Cycle complete *)
    bFault : BOOL;                   (* Fault status *)
    nFaultCode : INT;                (* Diagnostic code *)
END_VAR

VAR
    (* Internal Function Blocks *)
    fbSafety : FB_SafetyMonitor;     (* Safety logic *)
    fbRamp : FB_RampGenerator;       (* Soft start/stop *)
    fbPID : FB_PIDController;        (* Process control *)
    fbDiag : FB_Diagnostics;         (* Alarm handling typically uses a custom alarm manager FB that writes timestamped events to a Data Layer ring buffer. The ctrlX Alarming app (where licensed) provides the standard alarm pattern with severity classes, acknowledgement tracking, and historical logging to local or cloud storage. Simple projects use ad-hoc ST arrays of alarm structures and manual timestamping. *)

    (* Internal State *)
    eInternalState : E_ControlState;
    tonWatchdog : TON;
END_VAR

(* Safety Monitor - Use only certified safety components and PLCs *)
fbSafety(
    Enable := bEnable,
    EmergencyStop := bEmergencyStop,
    ProcessValue := rProcessValue,
    HighLimit := rSetpoint * 1.2,
    LowLimit := rSetpoint * 0.1
);

(* Main Control Logic *)
IF fbSafety.SafeToRun THEN
    (* Ramp Generator - Prevents startup surge *)
    fbRamp(
        Enable := bEnable,
        TargetValue := rSetpoint,
        RampRate := 20.0,  (* Illustrative value; tune and verify for the process *)
        CurrentValue => rSetpoint
    );

    (* PID Controller - Process regulation *)
    fbPID(
        Enable := fbRamp.InPosition,
        ProcessValue := rProcessValue,
        Setpoint := fbRamp.CurrentValue,
        Kp := 1.0,
        Ki := 0.1,
        Kd := 0.05,
        OutputMin := 0.0,
        OutputMax := 100.0
    );

    rControlOutput := fbPID.Output;
    bRunning := TRUE;
    bFault := FALSE;
    nFaultCode := 0;

ELSE
    (* Safe State - Implement dual-channel monitoring per category requirements *)
    rControlOutput := 0.0;
    bRunning := FALSE;
    bFault := NOT bEnable;  (* Only fault if not intentional stop *)
    nFaultCode := fbSafety.FaultCode;
END_IF;

(* Diagnostics - Rexroth projects favour the Data Layer Broker app for structured data logging, which exposes a subscription model similar to MQTT for any variable in the system. For high-frequency trace logging, the ctrlX Trace app writes directly to local SSD or cloud-connected storage. Simple projects can also use ST file-write FBs to append CSV records to the Linux filesystem directly. *)
fbDiag(
    ProcessRunning := bRunning,
    FaultActive := bFault,
    ProcessValue := rProcessValue,
    ControlOutput := rControlOutput
);

(* Watchdog - Detects frozen control *)
tonWatchdog(IN := bRunning AND NOT fbPID.OutputChanging, PT := T#10S);
IF tonWatchdog.Q THEN
    bFault := TRUE;
    nFaultCode := 99;  (* Watchdog fault *)
END_IF;

(* Reset Logic *)
IF bReset AND NOT bEmergencyStop THEN
    bFault := FALSE;
    nFaultCode := 0;
    fbDiag.ClearAlarms();
END_IF;

END_FUNCTION_BLOCK

Code Explanation:

1.Encapsulated function block follows Rexroth engineers lean heavily on reusab - reusable across Universal projects
2.FB_SafetyMonitor illustrates status checks and high/low limits; it is not a certified safety function
3.FB_RampGenerator prevents startup issues common in Safety Systems systems
4.FB_PIDController tuned for Universal: Kp=1.0, Ki=0.1
5.Watchdog timer illustrates one way to flag an unchanged output for diagnosis
6.Diagnostic function block enables Rexroth projects favour the Data Layer Broker app for structured data logging, which exposes a subscription model similar to MQTT for any variable in the system. For high-frequency trace logging, the ctrlX Trace app writes directly to local SSD or cloud-connected storage. Simple projects can also use ST file-write FBs to append CSV records to the Linux filesystem directly. and Alarm handling typically uses a custom alarm manager FB that writes timestamped events to a Data Layer ring buffer. The ctrlX Alarming app (where licensed) provides the standard alarm pattern with severity classes, acknowledgement tracking, and historical logging to local or cloud storage. Simple projects use ad-hoc ST arrays of alarm structures and manual timestamping.

Best Practices

✓Follow Bosch Rexroth naming conventions: Bosch Rexroth projects in ctrlX WORKS follow IEC 61131-3 naming with dot notatio
✓Bosch Rexroth function design: Rexroth engineers lean heavily on reusable function blocks packaged as ctrlX lib
✓Data organization: Rexroth projects use IEC 61131-3 global variable lists and PROGRAM VAR sections
✓Function Blocks: Arrange blocks for clear left-to-right data flow
✓Function Blocks: Use consistent spacing and alignment for readability
✓Function Blocks: Label all inputs and outputs with meaningful names
✓Safety Systems: Keep safety logic simple and auditable
✓Safety Systems: Use certified function blocks from safety PLC vendor
✓Safety Systems: Implement cross-monitoring between channels
✓Debug with ctrlX WORKS / IndraWorks: Use ctrlX WORKS debugger breakpoints in ST code rather than print-styl
✓Safety: Use only certified safety components and PLCs
✓Use a compatible simulator or isolated test rig to test Safety Systems logic before deployment

Common Pitfalls to Avoid

⚠Function Blocks: Creating feedback loops without proper initialization
⚠Function Blocks: Connecting incompatible data types
⚠Function Blocks: Not considering execution order dependencies
⚠Bosch Rexroth common error: Data Layer path typos — paths are case-sensitive and silently return null when m
⚠Safety Systems: Achieving required safety level with practical architecture
⚠Safety Systems: Managing nuisance trips while maintaining safety
⚠Neglecting to validate Emergency stop buttons (Category 0 or 1 stop) leads to control errors
⚠Insufficient comments make Function Blocks programs unmaintainable over time

Related Certifications

🏆Bosch Rexroth Certified Technical Specialist

🏆ctrlX AUTOMATION Developer

🏆Advanced Bosch Rexroth Programming Certification

Applying Function Blocks to Safety Systems using Bosch Rexroth ctrlX WORKS / IndraWorks requires understanding the platform, the process, and the project's acceptance criteria. This guide has covered implementation structure, an illustrative code example, verification practices, and common pitfalls for a advanced Safety Systems exercise.

Use the practices outlined here to create a design that can be reviewed and tested. Define performance targets in the project requirements and confirm them with repeatable measurements.

Next Steps:

1. Check Sources: Read the current ctrlX WORKS / IndraWorks help, controller manual, release notes, and relevant standards
2. Practice Safely: Adapt the example in a simulator or isolated training setup
3. Review: Have the I/O map, state behavior, faults, and recovery steps reviewed
4. Test: Record normal, boundary, fault, restart, and communications test results

Function Blocks Foundation:

Function Block Diagram (FBD) is a graphical programming language where functions and function blocks are represented as boxes connected by signal line...

Project duration depends on scope, reviews, hardware availability, software and firmware versions, testing, commissioning, and site constraints. Remember: Keep safety logic simple and auditable

For further learning, explore related topics including Temperature control, Emergency stop systems, and Bosch Rexroth platform-specific features for Safety Systems optimization.