In our most recent Technology Tuesdays podcast, Dave Hein — senior vice president and engineering and chief technology officer at Nexen Group — chatted with us about three brake options that now have Functional Safety certification. Listen in:
According to Pierrick Balaire, global business line leader at Intertek: “The Intertek Functional Safety mark provides Nexen a way to reduce hazards and risks to operating personnel, machinery, and surrounding environments at a time when they are facing increased demands around functional safety. We’re pleased to grant Nexen with this certification — the first of its kind in North America — and look forward to continuing to work with them and others providing the industry with high-quality products as well as peace of mind.”
According to Hein, Nexen has trademarked its functional safety-certified products under the NexSafe trademark name … and under this NexSafe name, the company currently has three products:
1. Rod Locks
2. Servo Brakes
3. Rail Brakes
1. Linear brakes for pneumatic cylinders — Nexen’s Rod Locks
The Nexen Rod Lock is a spring-engaged pneumatically released lock that clamps on a linear rod for safe holding or emergency stopping. Because the Rod Lock is spring engaged, it defaults to locking … and goes to a safe position in any power-off situation. If the machine loses pneumatic air pressure, the lock engages into the safe mode. If the PLC or PC controlling the valve (in turn controlling the lock) sends a signal to go into safe mode, the linear brake again defaults to lock into a safe position. Within this brake are springs that move a piston having an angled wedge that transmits and magnifies the spring force to a clamping collar. This in turn clamps the collar to the shaft with even and constant pressure around the diameter … a type of force application that’s important for smooth and consistent performance. Nexen offers the Rod Lock for every common shaft and cylinder size on the market today.
2. Brakes for traditional (rotary) servo motors — Nexen’s Servo Brakes
Nexen Servo Brakes also default to lock (in other words, a safe position) thanks to spring engagement. Then pneumatic releasing separates the brake’s friction surfaces to allow free spinning. Servo Brake products use a frustoconical friction facing — a fancy name for a friction facing having a taper on both the inner diameter and the outer diameter of the friction facing. Those surfaces apply the locking force via springs concurrently to both the rotating shaft and the brake housing to hold the shaft from rotating … all with zero backlash. In other words, the friction facing simultaneously engages both the housing of the brake and the rotating shaft. In fact, that’s the unique brake structure that is the basis for Nexen’s patent on the Servo Brake.
Most commonly these get designed in between a motor and a gearbox … and Nexen is able to customize the input and output to match what the customer motor or gearbox configuration is using requires.
Note: Frustoconical is the word used to refer to the shape of a truncated cone. The prefix frustum comes from Latin meaning piece.
Regarding the geometry of the friction surfaces, there is a cursory similarity between the cone-shaped mating set of other brakes and Nexen’s Servo Brakes. Some cone-type brakes have one tapered surface that engages between a rotating and a stationary element. In contrast, Nexen Servo Brakes have a cone with tapers on both the outer and inner surfaces — and that’s really a unique design feature. In effect that cone-shaped subcomponent can simultaneously contact two surfaces. Many engineering hours and energy went into correctly designing those tapers … with the main challenge being accommodation on of the normal wear arising from emergency stops and dynamic engagements … and addressing the fact that stresses in the part increase as the geometry of the part decreases.
To be clear, though: The Servo Brakes’ rotating surfaces are axially stationary … and the unit housing is axially stationary. The double-tapered frustoconical friction surface is actually what axially moves and engages both the stationary parts at the same time.
3. Linear brakes for linear profile rails and guides — Nexen’s Rail Brakes
Like the other NexSafe products, the Nexen Rail Brake also defaults to a lock (safe) position thanks to spring engagement and pneumatic release. The Rail Brakes paired with linear guide rails for positional holding as well as emergency stopping.
The Rail Brake uses a wedge to amplify the spring force, which is transmitted to the friction facings and the friction facing contacts on the rail’s non-bearing supporting part to hold the payload. A Rail Brake is offered for just about every common linear rail that on the market today … and in fact, NexSafe branded designs just mentioned are based off of previous robust versions of the products that have been in production for several years.
The Rail Brake comes in versions to fit everything from 15 to 55-mm linear rail … about 95% of the geometries most commonly used in motion system designs.
IIoT (Industry 4.0) functionality from sensor arrays in the brakes
Sensors in some of its brakes has helped Nexen transition from what it’s offered for the past several years into the NexSafe product families. According to Hein, what makes a NexSafe component qualify as NexSafe is sensing …
In the case of the linear brakes for linear profile rails and guides, a backpack package mounts on the end. This package contains magnetic field sensors to give feedback on the brake’s state. Among other things, the sensors tell the brake’s control system whether the brake is engaged or disengaged. This is useful as automated operations migrate to becoming smart facilities with smart machines.
Sensor feedback supports machine-condition monitoring as well as machine end-of-life predictions along with other situations potentially impacting uptime and throughput. The sensor feedback is also required for some of the safety category levels — and the backpack package allowed Nexen to achieve functional safety certification for categories B through 4 and performance levels a through e.
We learned in our chat with Hein that all three NexSafe brakes actually have integrated sensor feedback to deliver IIoT purposes … as well as functional safety for categories B through 4 and performance levels A through E. Essentially what Nexen has done for all three NexSafe offerings is deployed new sensor technology so the brakes serve as smart products that also happen to be compliant with ISO 13849 machine safety standards.
Related: Inductive proximity and magneto resistive sensors enhance IoT4.0 connectivity for Nexen brake families
The brakes in this series come with options aligned with safety and performance level categories that are part of ISO 13849 — with the standard product certified for safety categories B and safety categories 1. Even brakes without the backpack are functional safety certified … and designs needing higher levels of risk mitigation are served by Nexen offerings to satisfy even the highest requirements for risk mitigation.
All industries employ functional safety
Safety is a concept relevant to most all industries — and functional safety standards are top-level standards covering design protocols for many types of machines in many different types of industries. That’s in contrast with market standards dictating the safety requirements for specific machines such as punch presses and machine tools and palletizers. That said, brakes with functional safety certification have thus far seen the highest use in the most dangerous machines … those with automated knives moving blades executing processes that can cut people … including those for slicing plastic and paper webs. Industries with such machinery lead in deploying ISO 13849 risk-mitigation techniques.
Final note on the Rod Lock: It’s often quite useful that the linear brake use the same disengagement power source (that of pneumatics) that the actuator uses for its actuation. Nexen Rod Locks come in both standalone and cylinder-mount configurations: When engineers use the Rod Lock mounted to a pneumatic cylinder, one controller can execute commands over both.
On the horizon: More use of functional safety
Nexen’s investment in getting its brakes functional-safety certified was in part prompted by the industry shift to more robust machine safety. Plus the component and system supplier had engineers request sensor feedback to support Industry 4.0 functions. What’s more, ISO and IEC standards have been shifting to standardizing more robust risk-mitigation techniques … with new standards iterations every two to three years. Europe has traditionally led in machinery safety, though the U.S. has probably caught up and even surpassed Europe on some fronts. Nexen aimed to have products certified to support this technological trend.
Current applications for the safety brakes
Hein of Nexen reports quite a lot of interest in the new functional safety certified brakes — despite Nexen’s launching of the products during the COVID-19 pandemic. In one instance, a machine builder specified two Servo Brakes with the redundant feedback sensors for actuators on a vertical axis — a classic “hold the load” application to prevent personnel below from getting hurt — and essentially the highest risk situation, as the machine creates situations in which a human can lose life or limb. In fact, that’s called a Category 4 situation in the standard. NexSafe brake can be configured and used in such applications. Another OEM just purchased two Rail Brakes with two of the backpack sensor packages on each — again for a Category 4 situation.
“Nexen application engineers have the tools to help such OEMs (who may be unfamiliar with these newer machine safety standards) specify brakes that can meet required category and performance levels,” adds Hein.
For more information, visit this NexSafe deep link on nexengroup.com.
Filed Under: PODCASTS, Motion Control Tips