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Safety

Three ways to avoid motion-related safety pitfalls

Machine builders can help end users avoid motion-related safety incidents by performing risk assessments and ensuring proper equipment is installed.

By Todd Mason-Darnell and Pam Horbacovsky September 12, 2020
As the only controller to support two safety networks simultaneously, Omron’s NX-SL5 makes it easy to connect servos via FailSafe over Ethernet (FSoE) and enable safety control with fast cycle times for motion applications. Courtesy: Omron Automation Americas

 

Learning Objectives

  • Machine builders and engineers can ensure regulatory compliance by adding safety features to motion devices.
  • Risk assessments should be performed at all phases of development for a motion control product.
  • Installing safety control effectors into the power line is another good method to ensure safety.

By proactively designing safety into motion products, machine builders and engineers can ensure regulatory compliance. More importantly, they can protect future operators and strengthen relationships with end users.

Any automated motion inside a machine, such as a motor or servo, could potentially cause a serious accident. Following these three strategies can help machine builders and engineers can help reduce the risk of serious injury to users.

1. Have risk assessments performed at all phases of development

Risk assessments are essential for understanding a machine’s safety needs. Perform a risk assessment as necessary, with at least one at each of the following phases: the conceptual phase, the design phase, and upon the machine’s completion. It’s much easier and cheaper to design safety measures into a machine than it is to retrofit them in. End users will take note of this.

It’s a best practice to have risk assessments performed by an independent expert. This reduces the likelihood that anything could be left up to discretion or interpretation. An independent risk assessment provider can reduce the temptation to cut corners or judge risks to be less serious than they are.

2. Have a stop time measurement performed or calculated

Some safety devices, like light curtains, are designed to stop hazardous motion if a person crosses a certain threshold. However, it always takes time for machine motion to cease. To prevent injury, the safety device must be positioned far enough away that the person won’t reach the hazard source until the machine stops moving.

Stop time measurements, which ensure the mounting of safety devices at the minimum allowable distance to protect operators, should be done annually. If equipment limitations or application complexity get in the way of measurement, stop time should be calculated by adding up original equipment manufacturer (OEM)-provided info for each equipment piece along with an additional 10-15% to account for equipment variances and performance degradation.

3. Install safety control effectors into the power line, not the control circuit

There’s often a temptation to install a motor or servo’s safety control into its control circuit rather than into the power line. Unfortunately, if the safety system is activated, it will only shut off the logic to the motion device, not the power. If the control circuit were to fail, the motor or servo could still run and possibly endanger people nearby.

The reason people sometimes use the control circuit is it’s cheaper and easier. Safety devices are often rated by the amount of power that can go through them. It takes more power to install these devices on the power line as opposed to the control line. Nonetheless, it’s never a good idea to save money by sacrificing safety.

Machine builders can help end users avoid penalties by regulatory agencies as well as serious accidents caused by their machines by following these three recommendation. This, in turn, will improve the machine builders’ reputation and solidify a trusted relationship with customers.

Todd Mason-Darnell, Ph.D., marketing manager-services & safety; Pamela Horbacovsky, FS Engineering (TÜV Rheinland) and product manager – safety, Omron Automation Americas. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.

MORE ANSWERS 

Keywords: machine safety, motion control

Machine builders and engineers can ensure regulatory compliance by adding safety features to motion devices.

Risk assessments should be performed at all phases of development for a motion control product.

Installing safety control effectors into the power line is another good method to ensure safety.

CONSIDER THIS 

What additional methods does your company use to ensure machine safety?


Todd Mason-Darnell and Pam Horbacovsky
Author Bio: Todd Mason-Darnell, Ph.D., marketing manager-services & safety; Pam Horbacovsky, FS engineer (TÜV Rheinland) and product manager – safety, Omron Automation Americas.