What is a "Delta Robot?"

A delta robot is a parallel-link robot in which its major mechanical axes act on the robot faceplate in parallel rather than in series. This allows for both quick and precise movements.

History of the Delta Robot

Since its invention in the early 1980s, the delta robot has evolved into an innovative and high-speed solution for a wide range of assembly, picking, and material handling applications. With a three-axis delta robot, each axis is connected directly to the faceplate. The movement of these three axes (either one or a combination of all three) will move the faceplate in Cartesian coordinates. Optionally, a fourth axis can be directly connected to the faceplate to generate rotation. Because each axis only needs to accelerate the faceplate, significantly higher acceleration rates occur. This can notably reduce cycle times compared to a serial-link robot. Top speeds of 10 meters per second are typical for most delta robots. In addition to high speed performance, a parallel-link robot provides improved repeatability at the tool tip. This means that highly reiterative tasks such as in solar cell or other small part assembly, can be completed quickly and perfectly every time.

Three- and four-axis delta robots were initially deployed in limited picking and packaging industries. In these industries, products might be picked at random from fixed tooling and packaged into a shipping box, carton, or other type of container. These tasks can also be accomplished efficiently when several delta robots are used in one large picking and packing system which can handle an overall system throughput of several hundred parts per minute. Many different industries such as food, medical, electronics, cosmetics, and so forth, now make use of picking and packing systems.

Delta robots are now being used extensively in assembly or other applications in which high-speed and repetition must be achieved simultaneously. In many cases, these processes are done manually and can cause repetitive strain injuries or MSDs (musculoskeletal disorders). The U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) reports that, “According to the Bureau of Labor Statistics, MSDs accounted for 28 percent of all reported workplace injuries and illnesses requiring time away from work in 2009. (1)” Injuries, time away from work, and workers' compensation claims can cost companies billions. Incorporating robots into processes improves employees' quality of life, in addition to being a cost savings for employers.

Several M-3iA robots have recently been installed in industries including automotive engine facilities, and baking factories where they are used to score un-baked bread. The six-axis variant allows for the completion of tasks which involve manipulating parts and/or tooling at compound angles. By combining a three-axis wrist with the speed and precision of a delta robot, and the integrated iRVision offered by all FANUC robots, FANUC Robotics is rapidly making possible the automation of many tasks which are now either manual or done by expensive hard automation. With food, this can mean random-oriented, uniform or non-uniform products that may be fragile to the touch. A Senior Account Manager at FANUC Robotics notes that “a lot of existing processes are predicated on manual labor. It’s difficult for hard automation to mimic hand/eye coordination in picking random product off of a conveyor, particularly if it’s fragile and can’t be mashed into a corner or some other location where a hard-automation device can pick it. This is where robots come in.” Some examples of these applications are sorting cookies into containers, or pill or candy identification and packaging.

A food option is available with the M-3iA in which food-grade grease is used. The robot features a special coating to handle acid and alkaline disinfectants, and low-pressure rinsing. The M-3iA can work with primary (unpackaged) or secondary (packaged) food products, and has an IP67 rating for the entire robot which means it is waterproof and can withstand harsh environments, including dust and oil mist. Most robots designed for the food market feature an IP67 rating for the entire robot. IP ratings are a part of international IEC (International Electrotechnical Commission) standards, known as “intrusion protection” ratings. An IP rating of 67 means complete protection against any ingress of dust (specified by the first digit) and the ability to be completely immersed in water with no ingress of water (specified by the second digit). Food grade robots also have smooth external surface finishes meaning that there are no retention areas for food particles or bacteria.

Both force control and machine vision are becoming more and more prevalent as part of intelligent industrial robot systems, especially in high-speed assembly operations. Remote force sensing is now used to accomplish difficult assembly applications quickly using six axis delta robots. By remote mounting the force sensor, small six-axis delta robots are able to make use of this game-changing technology.

In an ideal world, parts line up and fit perfectly. However, in the real world workpieces often require a wiggle or visual adjustment, or are randomly presented. Machine vision and force control are increasingly able to handle these challenges and, when combined with a delta-style robot, the cycle time of each operation falls dramatically. This reduces the number of robots required and improves the return on investment timeline! Machine vision is increasingly used for inspection either before a part is put into an assembly or after the assembly process is completed, and delta robots can make this process quicker and more cost effective. How? By mounting a moveable camera on a delta robot, parts can be inspected very quickly and bad parts and/or assemblies can be eliminated and kept out of the supply chain. This keeps costs down and increases throughput. In picking applications for example, machine vision is employed in conjunction with conveyor tracking to track a randomly located product accurately on a moving conveyor belt at speeds as high 1400 mm/sec (275 ft/min).

The machine vision camera will continually snap and locate product upstream of the delta robots. When a product is identified by the camera, its location is combined with the current position of the conveyor belt. As the product enters a robot work area, the robot is able to move to the product precisely and either pick it or work on it while matching the current conveyor speed. Delta robots are the preferred style for this type of application since the amount of time the robot deals with each product needs to be as short as possible in order to maintain the usually very high system throughput. With assembly applications, the same concept is applied where machine vision is used in conjunction with a delta robot to locate and pick a specific part on a flexible feeding conveyor and assemble it to a mating workpiece.

Like all robots, delta robot deployments will continue to see strong growth as more and more operations across all industries embrace automation as a way to cut costs and stay competitive. When light payloads and very fast cycle times are required (especially in small work areas), whether it is assembly, picking, dispensing, or any number of other applications, delta robots will continue to meet the challenge.

Delta Robot Example Applications

A FANUC M-1iA high speed parallel link robot and an LR Mate 200iC robot can be used to assemble and disassemble solar panels. The M-1iA robot, equipped with iRVision® Visual Tracking, can pick randomly located solar cells and form an array of solar cells on an outbound conveyor.