Belt drives offer practical option for performance designs: Motion Trends report

Pulleys and sprockets need tight dimensional and geometrical tolerances to deliver top performance. Even narrow pulleys for tight enclosures can use shaft locks (such as the Shaftloc shown here) as it has engineered dimensions to transmit more torque than clamp or setscrew connections. In short, SDP/SI Shaftloc components connect pulleys to shafts without marring — for easy repositioning and synchronizing rotating components. The manufacturer aims to make this and other product robust — especially for miniature pulleys and sprockets, according to Cris Ioanitescu, application engineering manager.

Belt drives include belts and pulleys (as well as clutches and mechanisms for ratio variation) for power transmission between shafts. In cases where these drives function as a conveyor, the load rides on the belt. Elsewhere (as in actuators or machine-axis coupling) belt drives function as the device to convert rotary motion of an electric motor to linear strokes. Key benefits include vibration and shock damping.

Global Industry Analysts Inc. USA (GIA) projects that the global market for belt drives will reach $6.9 billion by 2022 — due in large part to demand for heavy industrial, conveyor, and construction equipment.

The U.S. is the largest market for belt drives, followed by Asia-Pacific (according to GIA, growing at a CAGR of 4.8%) thanks to rapid industrialization and the modernization of manufacturing plants and facilities.

In contrast with chain drives (more common in precision timing and high-torque applications) belt drives are relatively quiet and don’t require lubrication. According to GIA, demand for higher belt-drive efficiency is spurring increased use of metal belts — particularly for medical-device manufacture, conveyors, robotics, and solar-panel manufacturing.

Other trends include more use of aramid, polyamide, or polyester belts with rugged NBR elastomer covers (to maintain reliable belt-pulley friction). High-efficiency belt drives are also seeing continued adoption.

Yet another trend in motion design (including machines driven by belts and pulleys) is the rise of pre-integrated solutions — so that end users and even OEMs are now getting completely mechanically integrated units that go beyond just the one part or actuator to satisfy projects. “Much of our competition sells light subsystems or components,” said Michael G. Giunta, national sales manager for Macron Dynamics Inc., headquartered in Croydon, Pa.

Use of Cartesian robots with belt-driven axes has risen with automation. Macron Dynamics sells linear-motion systems based on traditional belt and screw actuation and is now working to offer these multi-axis machines as well.

“We too understand there’s a shortage of engineers in the market, and engineers are busier than ever. So there’s high demand from end users to get systems or products quickly. Some of what Macron Dynamics sells is predesigned multi-axis mechanical actuators and motion systems — fully assembled with connecting kits, hardware, cable tracks, and gearboxes … so the customer can simply add their own motors or end effectors,” explained Giunta.

An engineer trying to develop such a system on his own might need a week or maybe even two weeks of research and work.

As a lot of manufacturers that supply linear-motion components and Cartesian assemblies, the manufacturer does a lot of the engineering and the design work in advance using a Lego or erector-set mentality, as Giunta puts it — essentially taking a modular approach to component design.

“We have a detailed conversation with the engineer on the design requirements, and then quickly engineer and assemble subsystems. Part of this is understanding the weight and other characteristics of transported objects — and how fast they need to move. We start formulating a mechanical design that will work … and share some basic concept drawings … and then we go from there,” he added.

The company roots are in extrusions but then expanded into linear actuation — beginning with single-axis linear actuation and then the supply of multi-axis solutions … even to four axes. Many of the manufacturer’s Cartesian arrangements directly compete with robots such as SCARAs (in the case of the H-bot and the T-bot) or delta robots (in the case of the Macron Tri-bot, due out next year). Key advantages of Cartesian robotics over other options are price, higher payloads, and longer strokes.

When asked about the extrusions business, Giunta underscored that while Macron Dynamics still owns and uses its own (locally made) dies, it mostly produces extrusions for its own linear-product offerings — and to make them a bit more robust than other gantries on the market. This extends to even very large linear guideways and actuators, as in some of the 7th-axis robot tracks that the company makes.

“Macron Dynamics aims for innovation — so we don’t go off of a catalog or what’s commercially available, but aim to integrate materials and technologies to solve tricky end-user problems — with complete mechanical solutions that go beyond standalone components.”

One such application-specific mechanism improves belt drive reliability and safety. “A lot of people don’t trust belt technology in vertical arrangements … so we’ve developed a proprietary timing-belt design and CLAWS Mechanism — which is short for cam-lock arresting wedge system. Basically, the latter is a fully mechanical design that grasps the belt if it were to catastrophically fail,” added Giunta.

Click to enlarge this image. Belts can break if misused, overloaded, jammed, subject to shock or crashes, or degraded by contamination. In vertical belt-driven applications, this is particularly dangerous — because loads can fall if the belt breaks. Now a cam-lock arresting wedge system (CLAWS) Mechanism from Macron Dynamics slows and stops the load before it falls. In short, a retractable pawl hovers over a T slot in the actuator. A carbon-fiber-filled polymer belt dedicated to work with the CLAWS sits captured in this slot. Should the belt fail or break losing tension, a spring load drives the pawl teeth into this dedicated belt. Because the mechanism uses gravity to operate, it’s meant for vertical to 45° downward-sloping actuators. Macron Dynamics’ president Tony Cirone was spurred to develop the CLAWS by a local custmer that handles exotic materials and needed the material to get transported safely during all steps of production. A brake on the motor or a rail brake would’ve been insufficient, as this end user wanted to address what would happen if there was belt breakage.

That way, the payload on the carriage can’t fall — so imparts safety to protect personnel as well as the payload or product being transported. Otherwise, in applications in which tooling is very expensive, the CLAWS can prevent it from crashing into the ground or tabletop should it be holding an object should (in a rare occurrence) the belt fail. Essentially a charged system that uses springs, the CLAWS has a shuttle that can slide forward up an incline … and that incline can set itself into any part of the travel of the vertically oriented actuator and lock itself. The belt must actually break cleanly to trigger the mechanism to release itself with the slide and shuttle — to go up the incline and lock itself into another belt that also runs the length of the actuator.