Delta Robots Gain Greater Dexterity

The Delta, or parallel-link-style robot,has become well-established in industry as a high-speed solution by taking themotor mass that made it hard to quickly move a robot arm and placing it at thetop of the robot. Now, a new three-axis wrist is taking the Delta robot designconcept a step further by delivering wrist motions that allow the robot topick, spin and place objects at up to 2,000 degrees per second.

"We worked within the general design guidelines of a Deltastyle robot, which has three legs and all of the motors up at the top," saysMike Cicco, director of engineering for Material Handling robots at FANUC Robotics America Inc."But the bottom faceplate of these robots could not tip in any way; on somemodels it could rotate, but there was no way to change its orientation."

Looking at ways to improve the basic design, Cicco says FANUCRobotics looked at different methods to drive articulation down to the end ofthe robot arms. They decided to put three motors in line with the link arms ofthe robot itself and create a six axis version of its M-3iA robot with athree-axis articulated wrist.

"What we've done is put three small servo motors, one in eachleg, and each motor powers a driveshaft that comes out of the bottom," Ciccosays.

"The drive shaft attaches to a universaljoint at the bottom of the arm and then, within the wrist itself, a series ofprecise gears and reductions rotate each joint of the wrist mechanism."

The first motor spins joint four (J4) which rotates the firstaxis and basically spins the entire wrist. The next joint (J5) pivots the wristback and forth. And the last motor connected to J6 spins the metallic faceplateat the bottom of the robot.

A key to the FANUC Robotics design is that the universaljoint mounted on the side keeps the shaft length fixed. Cicco says it alsoallowed the company's four-axis version, which provides a single-axis wrist, tocreate a 20-mm-diameter hole in the middle of the wrist for air tubes. Afour-axis M-3iA with single-axis wrist is also targeting simple assembly andhigh-speed picking operations, but offers higher speeds - up to 4,000 degreesper second. In addition, the hollow wrist allows hoses and cables to be routedinternally, which minimizes wear and tear on the tooling cables.

Designed for Simple and Complex Assemblies

The new M-3iA parallel-link robot is designed to maximizespeed and flexibility for assembly, small part handling and pickingapplications, and is a larger version of the company's M-1iA robot introducedlast year. Both the four- and six-axis models can accommodate payloads up to6kg and Cicco says they have the largest work envelope of any robot in itsclass (1,350 x 500 mm).

The six-axis model and its three-axis, patent-pending wristmechanism are targeting more complex assembly tasks. The new wrist designenables the robot to pick up and insert parts at simple or compound angles, andtwist parts into place, similar to the flexibility offered by a manualoperator.

"The M-3iA's designmakes it possible to automate the assembly of a variety of applications thatcould not be done with traditional SCARA-type robots," says David Bruce,product manager for FANUC Robotics. "We refer to this series of parallel-linkrobots as fists, because they provide the accuracy and flexibility of a humanhand."

"The M-3iA is designedfor use in both the simple and complex assembly processes related toelectronics, medical devices, pharmaceuticals, cosmetics, office supplies,consumer products and solar panels," says Bruce. "A completely enclosedstructure also makes it safe for food environments."

With the fundamental speed advantage of the parallel-linkrobot and the increased flexibility the wrist provides for handling products,one goal for the designers is to explore the new types of motions that can becreated, as well as new application areas for the robot.

Delta-style robots are traditionally used in high-speedpicking applications in conjunction with vision systems to locate products anddo high-speed picking. But until now, applications have only been able to pickup objects, rotate them and put them back down in a different rotation.

"With packaging applications trying to reduce waste andproduct designers deciding what looks best for the product, many users wouldlike to have the robot be able to pick up a product that sits flat and put itdown either at an angle or standing straight up," Cicco says.

One application for the new technology is what's called "coinstacking" of cookies. In this example, the robots need to be able to pickcookies either straight up and down or at an angle, and load them into a trayat a different angle.

Another application is de-scrambling of bottles. When plasticbottles for shampoo or detergents are molded, they are often dumped into a bighopper. The idea is to find a bottle that is lying flat, pick it up, turn itright-side-up and load it onto the conveyor that goes into the filling line.

"The new robot adds the dimension of what we call pitch andyaw, and enables the user to do more than just rotate parts," Cicco says."Products can be turned up on end and placed at specific angles."

Another potential application is high-speed assembly oflarger products. FANUC introduced the M1iA a year ago, which is a much smallersix-axis version of this robot, but can only pick up 500 gm and has a smallwork envelope. The M6iA robot now offers a 6 kg payload and its work envelopeis a 1.35m-diameter disk. It can work in a cylindrical work area that is 1,350mm in diameter and 500-mm tall.

Yet another application involves complex assemblies, such ascertain consumer electronics applications, which might present the robot apallet of parts, and then use vision and force sensing to find the products andassemble them at all different angles.

Control and Vision Capabilities

According to FANUC, benefits of the M-3iA include thepatent-pending three-axis, parallel-link wrist and portable, compact size whichallows it to operate in small spaces. Use of the three-axis wrist also enables part feeding from the sides of a work zone, increasing the useable workspace. The four-axis version(single-axis wrist) moves parts at extremely high speeds; and the hollow wristallows tooling cables to be routed internally.

The core of the robot's innovation is a combination of the mechanicalconfiguration and the system's robot control software. On the software side,the biggest problem is enabling the robot to pick up a cookie and place itaccurately at a 30-degree angle on a moving straight line conveyor. The threeprimary axes of the robot basically need to position the wrist so that thewrist is in the right spot while tracking the conveyor. The three wrist axesare also moving in conjunction with the primary axes to keep that 30-degreeangle in a straight line. The kinematic solution implemented in the softwarehas to be able to coordinate all six axes at extremely high speeds.

The M-3iA, like all FANUC robots, operates with the company'sR-30iA controller with integrated intelligent functions such as iRVision^(R),Force Sensing, Robot Link and Collision Guard. The robot controller is based on the FANUC Series 31i CNCcontroller, offering the same brains, power and motion algorithm computingpower.

The iRVision system is a robotic vision package, available onall FANUC robots, that requires a camera and cable but no other additionalprocessing hardware. It offers a 2-D robot guidance tool to accomplish partlocation, error proofing, and other operations that normally require specialsensors or custom fixtures. For robotic vision processes that exceed thecapability of 2-D vision systems, FANUC offers an integrated 3-D vision system.

Click herefor more information on FANUC's Delta robots.

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