Machine Safety: Actuator controls versus machine actuators
Why is knowing the difference between a machine actuator versus an actuator control important? The hazard on a machine is what’s really important to reducing risk! Understanding two standards-based definitions can help.
Why is knowing the difference between a machine actuator versus an actuator control important? The hazard on a machine is what’s really important to reducing risk!
What is the hazard? Motion caused by a machine actuator can be a hazard to an operator, maintenance technician, set-up engineer, or clean-up personnel, to mention a few. However, the power (electrical, hydraulic, pneumatic, etc.) applied to the actuator control also can be a hazard to the same personnel. So, is looking at the hazard the best way to understand these terms?
Perhaps some definitions of these two terms may help clear up the confusion. Several international and domestic standards define:
- An actuator control as an operator control device used to initiate or maintain machine motion or other machine function(s). Some examples given include; two-hand control, treadle bar, foot control, inching button, e-stop device, etc.
- A machine actuator as a power mechanism used to cause motion of a machine. Some examples given include; air cylinder, motor starter, hydraulic valve, etc.
That said (and not to add more confusion) the machine safety standards also explain that a PSD (presence sensing device) device is an example of an actuator control. An example is when the robot arm retracts from a light curtain field initiating a signal to the machine control system to automatically cycle the machine. Or, when a “safe drive” automatically detects a fault and causes a Cat 1 machine stop. Where’s the operator in these examples?
Regarding machine actuators, I’ve also seen the metal rod inside an operator control device described as an actuator because it causes the contact(s) to open and remove power. Therefore, can a machine actuator also cause the stopping of a machine motion as well as causing machine motion? What about the friction clutch in a mechanical power press? Is this device a machine actuator since it either causes or stops motion and is powered via electric, hydraulic, pneumatic or spring type energy?
I believe by now the answer might be as clear as mud. So, what’s the point? It’s my opinion that this discussion is a good example where industry experts can help interpret the intent and requirements of machine safety industry standards. After all, has anyone ever seen a prescriptive Standard for compliance?
Has this presented you with any new perspectives? Add your comments or thoughts to the discussion by submitting your ideas, experiences, and challenges in the comments section below.
Contact: http://www.jbtitus.com for “Solutions for Machine Safety”.
- Events & Awards
- Magazine Archives
- Oil & Gas Engineering
- Salary Survey
- Digital Reports
Annual Salary Survey
After almost a decade of uncertainty, the confidence of plant floor managers is soaring. Even with a number of challenges and while implementing new technologies, there is a renewed sense of optimism among plant managers about their business and their future.
The respondents to the 2014 Plant Engineering Salary Survey come from throughout the U.S. and serve a variety of industries, but they are uniform in their optimism about manufacturing. This year’s survey found 79% consider manufacturing a secure career. That’s up from 75% in 2013 and significantly higher than the 63% figure when Plant Engineering first started asking that question a decade ago.