Functional Safety Acc. to ISO 13849 Development and provision of a hydraulic clamping system in compliance with the functional safety specifications of ISO 13849
HYDAC – your partner for complex hydraulic solutions in safety-relevant applications.
Machines need to be safe for the users and their surroundings
Machines need to be safe for the users and their surroundings. For this reason, machine manufacturers calculate and assess the hazards that their machine could pose and take measures to prevent damage from occurring. A safety-specific industrial standard applies for this, EN ISO 13849. It specifies the design principles and validation of safety-related parts of machine controls and must be complied with by machine manufacturers as part of the product development. For machine manufacturers and suppliers, this means that having a technology partner that can provide the required safety calculations on top of the technical realisation will reduce their workload enormously.
Providing support as a technology partner and system supplier
Our customer is a machine manufacturer that produces systems for welding large workpieces. The specific case involved a system for welding excavator base frames weighing up to 80 tonnes. The workpiece, rather than being clamped to a table, “floats” in the air, so that all the seams that need to be welded can be accessed perfectly. The 10 cylinders that are needed for this also align and centre the workpiece before it is clamped, to prevent it being deformed by the clamping process.
The safety assessment compiled by the machine manufacturer indicated that the workpiece poses a hazard if it is not clamped correctly or in the event of clamping system failure. The correct clamping procedure and the condition of the clamping system therefore need to be monitored. Furthermore, a safety reserve needs to be maintained so that the required functional safety is provided even in the event of system component failure. All in all, this had become a very complex task for the machine manufacturer. The manufacturer’s previous supplier had rejected the request because of the combination of the requirements for the clamping process itself and those for the functional safety. The machine manufacturer’s end customer recommended enquiring with HYDAC, as the customer had come to know and appreciate us as a skilled technology partner for various complex hydraulic topics.
Consultation and realisation of the system solution with HYDAC as project partner
Following the end customer’s recommendation, the machine manufacturer contacted us and asked whether we could get involved in the realisation of the system solution as a project partner. We then first carried out an extensive analysis with the customer to determine the configuration of the potential system solutions.
We developed a special block with redundant directional poppet valves and switch position monitoring. Each of the clamping cylinders is controlled by its own block, and each block is supplied centrally by a variable-speed hydraulic power unit. The monitoring of the switching statuses of each individual block serves as the basis for the control of all the other blocks. To realise the required emergency operating characteristics, each block has its own diaphragm accumulator that provides sufficient hydraulic power to enable a safe machine stop in the event of hydraulic supply failure. These accumulators are also equipped with a sensor system to monitor the pre-charge pressure (P0 monitor).
The required performance level was realised by this solution. We were able to verify this with our calculations, which the customer then integrated into the customer’s own Sistema calculations.
Working with HYDAC enabled the customer to solve the problem efficiently without having to involve any other suppliers. The customer received the perfect solution: a safe and ready-to-install hydraulic subsystem for centring and clamping workpieces. The customer was able to integrate the safety verification documents included in delivery into the higher-level system calculation.
“With HYDAC as a partner, we found a solution for the clamping issue that was optimal in terms of both process reliability and user safety. As HYDAC used its expertise to take care of the issue, we were able to concentrate on our core competencies.”