In industrial environments where machines operate with significant force and speed, ensuring operator safety is of utmost importance. Two-hand control in industrial automation, also known as Two-Hand Control Devices (THCD), is a mechanism designed to eliminate the risk of accidental machine activation and contact with moving parts. According to the ISO 13851:2019 standard, these devices require simultaneous engagement of both hands by the operator, effectively minimizing accident risks.
This article delves into how two-hand control should function according to standards, explores the technical aspects of its construction, and highlights common implementation errors.
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Types of Two-Hand Control Devices – Choosing the Right Solution
Two-hand control is a mechanism that forces the operator to use both hands simultaneously to activate a machine. This significantly reduces the risk of accidental contact with moving elements. The ISO 13851 standard outlines the requirements for such systems and categorizes them into three types, depending on the level of safety they are intended to provide.
What Are the Types of Two-Hand Control?
Type I – Basic Protection
This solution offers the lowest level of safety (PL c/SIL 1). In this case:
- No synchronization of buttons is required – they can be pressed at different times.
- No reinitialization is required – the machine can be started with a single press after release.
Where to Use?
Machines with low risk, where other safeguards minimize danger, such as fixed guards. Example: assembly devices with limited force and speed.
Type II – Enhanced Protection
This type offers a higher level of safety (PL d/SIL 2) and introduces additional requirements:
- No time synchronization between button presses is required.
- The operator must release both buttons and press them again to start the machine (reinitialization requirement).
Where to Use?
Machines with moderate risk, such as medium-sized presses, where the risk of contact with the tool is higher, but injury consequences are not critical.
Type III – Maximum Safety
The highest level of protection is provided by Type III (PL e/SIL 3), which introduces:
- Time synchronization – both buttons must be pressed within 0.5 seconds.
- Reinitialization requirement – after releasing one of the buttons, both must be pressed again.
Subtypes:
- IIIA: Simpler configuration (button contacts connected in series), limiting diagnostics.
- IIIC: Each button is connected independently, ensuring better fault detection.
Where to Use?
High-risk machines, such as high-force presses, bending machines, or industrial hammers. Type IIIC is ideal where reliability and precise safety diagnostics are required by risk analysis.
How to Choose?
Selecting the appropriate type of two-hand control depends on:
- Risk Assessment: What hazards are present when operating the machine?
- Machine Characteristics: What are the speeds, forces, and modes of operation?
- Functional Requirements: Is synchronization and reinitialization necessary?
For instance, a machine with high-speed moving parts and significant force, such as an industrial press, should have Type IIIC two-hand control, which provides the highest level of safety.
The ISO 13851:2019 standard clearly defines the requirements for two-hand control devices, tailoring them to different risk levels. The final choice of type depends on the machine’s specifics and risk assessment results. When it comes to safety, there is no room for compromise – selecting the right two-hand control system is fundamental to protecting operators in the industry.
If you need assistance in matching the system to your application, you can always rely on support. Together, we will find the best solution.
Legal Status
According to the Machinery Directive 2006/42/EC (Annex V) and the Machinery Regulation 2023/1230 (Annex II), two-hand control panels are considered safety components. They must meet specific technical requirements and undergo conformity assessment procedures. Although they are not strictly machines, they fall under essential requirements!
Conformity Assessment Procedure
As safety devices, two-hand control panels undergo EU type examination (module B) and internal production control (module C). After completing the assessment, the manufacturer places the CE mark, confirming the product’s compliance with regulations and safety requirements. Two-hand control panels play a crucial role in protecting operators and, thanks to compliance with standards and legal regulations, are a reliable solution in industrial applications.
Integrating Two-Hand Control with Machine Run-Down Time
Machine run-down time is a crucial parameter to consider when designing machines and safety systems. The PN-EN ISO 13855 standard specifies that the distance between the operator and the danger zone must be such that the machine stops before the operator reaches the hazardous elements. This includes the system’s reaction time and the speed of the operator’s hand approach.
Example:
- Machine run-down time: 300 ms (0.3 s).
- Operator hand approach speed: 2 m/s (according to the PN-EN ISO 13855 standard).
- Minimum distance from the danger zone: d=t×v=0.3 s×2 m/s=0.6 m
The two-hand control buttons must be arranged so that the danger zone is at least 600 mm from the operator. This ensures that the machine stops before the operator has a chance to touch its dangerous parts.
Two-Hand Control in Different Environments – Electric and Pneumatic Energy
The ISO 13851 standard applies to two-hand control devices (THCD) regardless of their energy source, meaning they can be designed in both electric and pneumatic versions. The choice of the appropriate power type depends on the machine’s working conditions, including specific requirements for explosion hazard environments (ATEX).
Pneumatic two-hand control is an ideal solution for machines operating in harsh environmental conditions, such as high humidity, dust, or explosion-prone atmospheres (ATEX). By eliminating electrical components, these systems minimize the risk of sparking, making them indispensable in EX environments, such as the chemical and petrochemical industries. A simple design based on 3/2 valves, logical “AND,” and pneumatic brakes ensures reliable operation even in extreme conditions.
FAQ: Two-Hand Control
There is no obligation to use harmonized standards, but their use provides a presumption of conformity with essential requirements. If not used, an alternative solution ensuring sufficient safety must be demonstrated. The standard specifies design, functional requirements, and classification into three device types based on safety level (PL/SIL).
In Type III devices, both buttons must be pressed within 0.5 seconds. If this time is exceeded, the device will not generate an output signal, and reinitialization will be required.
Yes, pneumatic two-hand control systems are best suited for explosion-prone zones. By eliminating electrical components, they minimize the risk of sparking, making them a safe choice in EX environments.
Type I offers basic protection without synchronization and reinitialization (PL c/SIL 1). Type II requires reinitialization but not synchronization (PL d/SIL 2). Type III provides the highest safety with synchronization (≤0.5 s) and reinitialization (PL e/SIL 3).
The choice of system depends on risk assessment, machine specifics, and working environment. High-risk machines, such as industrial presses, require Type III systems, which provide the highest level of operator protection.