Robotic grippers have made headlines recently, mostly thanks to breathtaking new prosthetics, smarter material-handling machines and fairly brisk robotic innovation. However, traditional pneumatic grippers still dominate industrial-assembly and robotic applications. That’s because pneumatic grippers are reliable, come in myriad sizes and grip quickly.
This gripper from Robotiq is a universal adaptive gripper with two fingers. Here, it’s grasping a part with an inside grip. According to Robotiq’s Bouchard, there are no quantum leaps in robotic-gripper technology. “It’s a relatively small-volume market with a lot of hardware and software development in an environment with no standards … and engineers want to ensure that a gripper product is mature before putting it on critical paths of manufacturing lines. Even advanced grippers must live in existing ecosystems that evolve slowly.”
They’re also cost effective and simple to control, according to Peter Farkas, president of American Grippers Inc. (AGI).
“Pneumatic grippers are the most common end-effector type in everything from industrial production to cleanroom environments … mostly because they’re compact, lightweight and offer a high force-to-weight ratio to benefit high-speed assembly machines,” said Farkas.
But whether they’re pneumatically or electrically actuated, one dominant gripper trend is toward right-sized industrial grippers.
“Fifteen years ago, engineers often over-specified grippers because they wanted to keep the design process simple and play it safe with machinery that could most definitely do the job,” said Walt Hessler, V.P. of sales at PHD Inc.
“Today, the trend is toward right-sized grippers because the popularity of sizing software—online and downloadable, ours and others—is simplifying the job of specifying grippers.”
This lets machine builders reduce gripper weight, a helpful detail considering how fast some SCARA robots spin and move about. Consider the enormous moments a 10-lb gripping head fixed to a quick-moving robot-arm end can create. In contrast, smaller end-of-arm tooling lets engineers pick upstream robot components that are smaller and more efficient.
Another trend is higher gripper reliability. “We serve applications that must hold tight tolerances in the manufacturing of the products, so most of our grippers have repeatability that’s tighter than 10 µm,” said Jesse Hayes, automation group manager at Schunk. “Not every application needs it, but that repeatability brings reliability.”
Still another trend is toward grippers with larger pistons for better load bearing to let smaller grippers handle heavier parts.
In fact, it’s ultimately the size, force and shape of the parts that the machine must grip that dictate the most suitable gripper. Will the gripper pick parts off a conveyor? Will it take the form of a three-jaw gripper to grab round items? Would the setup work better with a long-law gripper capable of grasping different workpieces? All of that is relevant information, said Hessler.
Automotive drives innovation, with other markets rising
Historically, the biggest driver of industrial-gripper innovation has been the automotive industry. “GM, Ford, Chrysler and Honda all use grippers to manipulate car-body panels and other pieces of sheet metal,” said Hessler. “From the beginning, the automotive industry has driven robotics … and this is true today,” confirmed Robert Little, CEO of ATI Industrial Automation. His company doesn’t produce grippers, but myriad robotic end-effectors including robotic tool changers.
Here, despite a lot of standardization on pneumatics, industrial-gripper manufacturers are designing increasingly job-specific grippers.
“AGI just developed a gripper to grab O-rings from their IDs and place them into bores to reduce repetitive stress injuries (RSIs) in workers that once performed the task,” said Farkas. Automating O-ring seal installation and O-ring assembly removal saves companies money.
Related article: Five ways to get the most out of pneumatic grippers
Here’s a gripper from American Grippers Inc. Compressed shop air to operate it is readily available in most plants. Pneumatic grippers also weigh less than motors and drive mechanisms.
“Or consider how automotive companies now use bus systems to communicate and pass huge amounts of sensor data for robotic tooling. This takes robotic tool changers that can work with DeviceNet, Industrial Ethernet, PROFIBUS and PROFINET and other busses,” said Little.
He added that users of heavy-duty robotic tool changers now ask for safety devices so changers can’t be separated outside a tool stand … so his company now sells a safety system that removes and reconnects power automatically.
Besides the automotive industry, other industries spurring changes in robotic-gripper design include electronics, appliances and consumer products, according to Samuel Bouchard, president at Robotiq, Quebec, Canada. That’s because manufacturers here must adapt quickly, with product lifecycles shorter than ever.
“At the same time, the demography and shortage in skilled employees is an incentive to automate tasks currently done by human operators,” he said.
Hayes also sees an increasing number of design engineers with new applications, due to the onset of collaborative robots. Many of these designers have never used robots or grippers before. “Here, we see a shift towards electric grippers. That’s because sometimes the gripper or end-of-arm tooling is the only pneumatic device associated with a robot and designers want to consolidate,” said Hayes.
Yet another industry that has grown since 2008 is the aerospace industry. “Aerospace does much smaller volumes, but requires highly complex tooling in the handling and making of aircraft,” said Little. He added the packaging and food industries and increased use of composites has also spurred more robotic installations with grippers and other end effectors.
This low-profile GRPL Gripper from PHD Inc. makes long strokes and has synchronized parallel-jaw motion to automatically center items for operations such as sorting. The long stroke compensates for items of varying size or position. A rack-and-pinion synchronizer minimizes backlash.
Adaptive grippers and prosthetic inspiration
Even for industrial applications, gripper designs are increasingly diverse. For example, AGI’s specialized O-ring gripper can’t be classified as a two-jaw parallel or an angular gripper. Other grippers that don’t fall into neat categories include single-jaw grippers, three-jaw grippers, bladder grippers that inflate against part ODs and IDs, and magnetic grippers. “In fact, the latest grippers are adaptive grippers that are blind to shape or capable of dexterous manipulation,” said Farkas. These robotic grippers wrap around and adapt to parts of varied sizes.
Farkas noted three such grippers from other robotic companies:
• A soft robotic gripper called the Versaball from Empire Robotics works by jamming granular materials. A sand-like material fills the green ball; a pump fills the ball with air to soften it, and an arm pushes the gripper into an object. Then the pump drains air from the ball, and the sand granules jam together and harden around the object.
• Another gripper from Grabit uses static electricity to grasp objects. In fact, electroadhesion technology could soon revolutionize robotics, material handling and industrial-automation gripper tasks.
• A rubber-jointed iHY robot gripper (originally developed by iRobot and Harvard and Yale researchers for a DARPA ARM challenge) can use a power drill, change a tire, and unlock a door with a key.
“We also make self-adaptive electric grippers,” said Bouchard at Robotiq. “Similar to a servo drive, designers can control the position, speed, and force of the fingers. These articulated fingers can adapt automatically to various shapes.” The grippers make internal, external, parallel and encompassing grips.
It’s true that there’s been a rise of easy-to-program collaborative robots—including the low-cost arms of Universal Robots and Rethink—for modest assembly and material-handling tasks. But as Bouchard points out, if an engineer must design and build custom tooling every time he wants to reprogram the robot, he’s not leveraging its full capacity. That’s where his company’s flexible grippers excel.
This gripper form MIT researchers uses a GelSight sensor with an array of colored lights that channel down different faces of the cubic housing to make three-dimensional measurements.
Others also note the limitations of whiz-bang gripper innovations. “We make products that try to mimic the functions of a human hand. Will this be the future of robotic grippers? Probably not, but we do learn lots of things during development and commercialization of such grippers,” said Hayes. He sees expansion of applications where flexibility outweighs performance and generic grippers that can handle a variety of products where one robot will be required to do many different tasks. That is where specialty grippers excel. Even so, a broad selection of standard grippers satisfies most applications.
Prosthetic and industrial-gripper inroads
Though prosthetic-gripper technology is completely different from that for industrial grippers, there are areas of convergence. Consider the robotic hand that uses Micromo servomotors for more delicate operations. Or consider the GelSight gripper, a design started at MIT in 2009 and released in a high-functioning version last year. It uses a small sensor on its gripper finger and a super-fast processing algorithm to give the robot feedback in real time. Industrial robots are capable of remarkable precision when the objects they’re manipulating are perfectly positioned in advance. But according to Robert Platt, professor at Northeastern and the GelSight’s robotics expert, the gripper’s fine-grained manipulation is unprecedented for a robotic end-effector operating on the fly.
Tool changers evolve as well
This two-finger gripper from Robotiq can make adaptive movements. Here, it’s grasping a part with a wrap-around grasping gesture.
Just like grippers, robotic tool changers are also evolving. “We have a robotic changer designed for handling food. Here, operations wash changers down with high-pressure cleaning solution,” explained Little. The problem is that when a traditional tool changer is separated, it exposes sensitive areas such as electrical contacts and greased locking components. So, his company developed a changer that resists washdown when locked, with a tool side than can be cleaned separately. This required special materials, an internal electrical system and unique seals not available 10 years ago.
“Over the years, robotic tool changers in general have become reliable,” said Little. He added that many tool-changer companies have gone out of business (or nearly so) due to unreliable designs. “But the newest tool changers use myriad sensors to indicate lock, unlock, tool presence and ready-to-lock status. These sensors are critical to the safety of the product,” said Little. Today’s tool changers have also become stronger.
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Filed Under: Bearings, Pneumatic equipment + components, ELECTRONICS • ELECTRICAL, Robotics • robotic grippers • end effectors
