Moving into the future

If the automation industry trend-spotters are right, we are on the verge of Industry 5.0, where humans and machines interact more effectively to leverage the unique benefits of each. As part of expanded cyber-physical interaction or the extended internet of things (EIoT), there will be more axes of motion to benefit from automation. Standard linear motion technology will continue to drive the bulk of applications in this space, and targeted customisation with a foundation of standard products will make the transition smooth and cost effective.

Linear System Design Tips

1. Consider the environmental conditions under which the system will operate, including temperatures, dust and dirt levels, chemical exposure, washdown processes, vibration and shock load, and radiation. Fully enclosed units that use a cover strip may be required for dirty and/or wet environments, but in clean factory environments, open designs may provide cost savings and enhanced design flexibility. In extremely dusty environments, fully enclosed units can be equipped with a positive air pressure system to purge any particles that may get through the cover strip.

2. When defining the direction and magnitude of your load, the system orientation can be important. With a horizontal orientation, the drive load is equal to the payload weight times the frictional coefficient, while with a vertical orientation, the drive load is equal to the weight. For vertical applications, know that the mechanics alone may not be enough to hold the load when it is stationary, and an external brake may be needed. This could extend the overall length of a unit.

3. For applications that require accurate positioning, preloaded ball screws or high-precision lead screws can be used, and the mounting surfaces of the rails can be machined.

4. Lead screw drives, which are used in low to medium duty cycle positioning applications, operate at low noise levels and provide excellent repeatability of 0.005 mm.

5. Purchasing a configured linear motion system can typically reduce engineering time and assembly cost by 90% or more, while providing a 20-30% cost savings in material.

Electric linear actuators are raising material handling to new heights. As digital transformation extends the scope of automation to more axes and electric linear actuators handle increasingly heavier loads, more material handling system designers are converting hydraulic and pneumatic motion control to electric, especially in new projects. Linear actuators suppliers are responding with innovations that extend the scope of material handling automation in load management, sizing, intelligence, durability, energy efficiency, safety, and ergonomics.

 

Electric linear actuators increasingly offer sophisticated, advanced capabilities for material handling automation. Whether it be the peripheral intralogistics of conveying and transporting or support for production processes such as feeding and filling, material handling is increasingly vital to industrial operations. (Figure 1)

In an assembly operation, for example, linear actuators might feed materials, manipulating them to optimize access to work surfaces or diverting objects from one conveyor to another. In a food packaging operation, to take another example, setting up can consume up to half the work cycle. Linear actuators might reduce that time by automating the unfolding of cardboard or cutting film.

Electric actuators can also expand the controllable working radius, carrying materials toward or away from processing. They might support motion on forklifts, automated guided vehicles (AGVs), telescopic lifting units or overhead conveyors.

• Physical properties. Material handling automation developers must consider the shape, weight, size, position, and direction stability of packages moving along a plant or conveyor system. They also must consider how the package materials affect their rollability, slide-ability, stack-ability, surface sensitivity, and stiffness.
• Environmental parameters. Material handling equipment designers must consider parameters such as room layout, machine size limitations and available degrees of freedom.
• Motion parameters. Like most motion control applications, material handling applications consider weight and inertia of the payload as determined by speed and acceleration within cycle times and the required accuracy.

Long life – Material handling applications often run 24/7 in set-and-forget applications. Production line applications, such as an arm that diverts items from one conveyor belt to another, have high duty cycles and are subject to wear and tear. AGVs, forklifts and other mobile equipment may be deployed in those applications and usually run on batteries. (Figure 3) Equipment that is used outdoors or in hazardous environments, and subject to ingress from moisture and dust can also require long life.

Figure 3. For AGVs without human involvement, remote control over radio, WiFi, satellite and other communications is vital. In addition to their remote benefits, electric actuators reduce maintenance and environmental concerns thanks to sturdy designs. This all-in-one actuator package makes it possible for AGVs to move goods over larger areas no matter how demanding the conditions.

Linear actuators using brushless motors can have duty cycles of 100 percent and up to 600 km (375 miles) of maintenance-free life. This long life is a major advantage over hydraulic and pneumatic technologies, which require almost constant maintenance.

 

Plus, lubrication technology has advanced to the point where some actuators are factory lubricated for life.And adherence to IP standards of IP65, IP66 and IP69K prevent particulate, moisture and other ingress that can shorten life.

 

Safety and ergonomics – Material handling equipment constantly puts humans at risk. For example, a machine that loses power may drop its load faster than a human can get out of the way. There might be ergonomic challenges resulting from repeated movements or awkward workpiece positioning.

 

Electric linear actuators aid in these situations with electromechanical and static holding brakes, which hold the load in place in case an application loses power. They can also make work safer by raising, lowering, or tilting worktables to comfortable, more ergonomic angles.

 

Automated picking helps avoid long feeder routes and relieves the operating personnel from the work cycle of the machine as much as possible, keeping ergonomics and safety a priority. (Figure 4) Also, replacing hydraulic cylinders removes the risk of slipping and falling on leaked fluid as well as product contamination from solid fluid leaks.

 

 

 

What’s the return?

To calculate the most accurate ROI with the right amortization on a custom project for both the OEM and the end user, designers must make procurement decisions in the context of the entire product lifecycle, including production costs, ongoing operating costs and potential productivity. Likewise, the decision should factor in the benefits of integrating the latest technology, such as onboard electronics, which contribute to greater competitiveness for the OEM and benefits for the end users.

 

Electric actuators are the key technology making the connection between this emerging digital world and the physical world. Up until quite recently, this gap had been too wide to span. But now that electric actuators are stronger, smarter and more affordable, the chasm is no longer so daunting. Electrification is ushering in a new era of efficiency, which will contribute to better automation, improved material handling and, ultimately, better business.

 

More than eight million Americans and Canadians rely on canes or crutches, and most share one challenge: placing it conveniently out of the way when not in use. With the help of Thomson Industries, Inc., a team of engineering students from the University of Waterloo (located in Ontario, Canada) has prototyped a potential solution, using an electric linear actuator assembly that enables a crutch to automatically stand on its own.

There’s got to be a better way

After conducting research of challenges faced by disabled people, the Waterloo engineering team was amazed to see how disruptive crutches were to the daily activities of their users. “If you simply want a glass of water, you can’t just let go of your crutch; you need to find a way to support it,” said Connor McCallum, the team’s electrical design co-lead. “If the crutch falls, picking it back up can be difficult, especially for someone with a disability. And what do you do in a restaurant? A server might store it away for you, leaving you with no mobility options.”

These observations led the team to devote their mechanical and electronic engineering talents to developing a new crutch solution for their senior project. The students envisioned a crutch that could automatically stand on its own, freeing the user’s hands to perform routine activities more conveniently without losing immediate access to the support if they need it.

Bringing the vision to life

The Waterloo team roughed out a CAD design that outfitted the bottom of the crutch with small legs that would automatically extend or contract in tripod fashion after removing the crutch from beneath the armpit or letting go of the handle.

When extended, the legs would form a base about four inches wide, enough to support the crutch. For additional stability, the students envisioned a set of smaller legs that would brace the primary legs from the inside. They hypothesized that controlling leg operation would require a motor-driven rotating linear motion assembly of some sort and conducted an online vendor search, which led them to Thomson.

A consultative approach

On the Thomson website, the students quickly found their way to the stepper motor linear actuator section. These components combine a hybrid stepper motor and a precision lead screw in a compact envelope that they thought would work well at the end of the crutch. Using the Thomson online product selection tool, they entered expected motion parameters and saw a solution begin to take shape. To further refine their product selection, they followed a link to schedule a live virtual design consultation with a Thomson engineer.

“The students shared an early 3D model of their concept, which provided a solid basis for our discussion of exactly what they wanted to accomplish,” said Kyle Thompson, product innovation manager at Thomson. “We discussed stroke lengths, move distance, move time, speed and acceleration/deceleration options  ̶  all guided by our online design tool.”

Marching the design forward

As the collaboration continued, the required motion assembly began to emerge. A stepper motor would rotate a threaded shaft along which the nut would ride. The nut would attach to the two collars, which would move along the core axis of the crutch. One collar would attach to the main outer legs (Figure 1, in red); the second collar would attach to the inner supporting legs (Figure 1, in green.) A single actuator would drive both collars.

To extend the legs, the motor would translate downward force through the nut to move both collars downward until the lower collar hits a hard stop, locking the inner legs into their bracing position. The upper collar then continues along its downward path, extending the primary legs outward to form the tripod that enables the standing. Reversing the motor rotation reverses this operation and retracts the legs.

Figure 1. The crutch’s double-collared system features an upper collar (red) that guides the main telescoping legs and a lower collar (green) that guides the internal bracing legs.

 Working with the tool and in collaboration with Thompson, the Waterloo team submitted its wish list of specifications. The actuator assembly had to support up to roughly 300 pounds of force; the legs had to open and close in less than a second with a travel distance of about two inches; it had to run on lightweight battery power; and ultra-high precision was not necessary.

The analysis concluded that a Thomson stepper motor linear actuator powered by a 12-volt battery would be right for the prototype. It could easily meet the force requirement; a NEMA 23 stepper motor would drive motion in less than a second; a six-inch-long lead screw would support more than the two-inch desired stroke; and a standard actuator would provide the precision needed. Although this satisfied the motion profile, Thompson advised the team that one more challenge needed attention.

Anti-rotational guidance

Because the nut must be free to move up and down the rotating screw, it might also rotate along with the screw, interrupting smooth operation. To prevent this, Thompson helped the team customize an L-shaped block that interfaced with the nut and rode with it along the main axis. The block was also fixed to a bushing guided by a shaft that was anchored to a plate just below the motor. (Figure 2)

“The Thomson virtual design session helped narrow our choices to determine exactly what product we needed to meet our design specifications,” said McCallum. “The online tool was easy to use and got us going, while Kyle was instrumental in helping us customize and optimize our motion. The way in which they helped us solve the anti-rotational issues is a great example of why it helps to have consultation with a motion design expert.”

When deployed, the crutch has a four-inch radius, and the inner supporting legs are at 40 degrees from the vertical. Deploying the outer legs at angles below 45 degrees prevents them from flipping inside out when they retract to their undeployed state. (Figure 3)

Expansion or contraction speed is 0.6 seconds with a travel distance of two inches, which is about 3.33 inches per second. The team intentionally restricted the top speed to prevent damage to the crutch prototype. The load-bearing components accommodate up to 300 pounds.

As illustrated in the purple sections of Figure 4, the team distributed the electronics evenly throughout the crutch frame to achieve optimal balance. A microprocessor in an electronics box near the top of the crutch frame receives analog signals from pressure sensors located in the armrest, handle and bottom, and sends them to the motor controller located in a box below it.

The motor controller would connect to the lead screw via wires fed through the hollow tubes of the crutch, although wires were exposed on the prototype. Limit switches were used to detect the position of the legs. The legs were controlled using pressure sensors on the crutch to determine if the crutch should be standing, if it is not in use, or if it should retract so that the user could walk with it.

Figure 4. Self-standing crutch electrical controls.

Pressure sensors had to be compatible with natural human use. The bottom sensor, which signals whether the crutch is in contact with the ground, requires a relatively low threshold for activation. The armpit and hand sensors, on the other hand, trigger motion of the legs and require a slightly higher pressure threshold to prevent the legs from operating prematurely. A three-button control panel located just above the motor controller electronics box would enable the user to override the automatic controls.

Making good better

Once the team assembled the electrical and mechanical components, and integrated them within the crutch, it successfully stood up in its use case and met all desired requirements. The crutch automatically detected when it was left alone and responded accordingly. It was also able to toggle between manual and automatic modes.

Now that the Waterloo team has a working prototype in hand, they are reflecting on what might be done to improve the crutch’s operation. That would include making it more aesthetically appealing, using printed circuit boards, different materials and a smaller motor to save space and make it lighter, and feeding wires through hollow tubing instead of leaving them exposed. Wherever their vision takes them, they can be certain that the Thomson team will be standing right there beside them.