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How many types of multi-joint, multi-axis collaborative robots are there, and how do I choose the right one?
Robots are used in various fields such as healthcare, food and beverage, steelmaking, and warehousing to complete tasks faster, more reliably, and/or more cost-effectively. Robots are even employed in the assembly of new robots. Robots come with one to seven axes, each providing a certain degree of freedom. A two-axis Cartesian gantry typically operates on the XY or YZ axes. Three-axis robots have three degrees of freedom and perform their functions through XYZ axes. These compact robots are rigid and cannot tilt or rotate, though they can be equipped with tools that can rotate or adapt to small payloads. Four-axis and five-axis robots offer additional rotational and tilting flexibility. Six-axis articulated robots have six degrees of freedom, allowing for flexible movement and rotation of objects in any direction. These six-axis robots are often chosen when applications require complex manipulation of large or heavy objects. Seven-axis robots provide extra orientation capabilities within confined spaces to manipulate tools. Compared to other articulated robots, they can operate closer to the workpiece to save space.
Articulated Robots
The popularity of six-axis and seven-axis articulated robots reflects the great flexibility of six degrees of freedom. They are easy to program, come with their own controllers, and allow programming of motion sequences and I/O activation via user-friendly teach pendants. They can have extensive reach, with some models exceeding three meters. This size range makes articulated robots suitable for numerous industries and applications involving manufacturing or moving materials or finished products.
By design, articulated robots occupy space and footprint that cannot be used for other purposes. They also have singularities—positions and orientations within the surrounding space that they cannot access. These spatial limitations necessitate more complex safety precautions since robots are often used in areas where workers are present.
Cartesian Robots
These robots are adaptable, easy to install, and maintain. The travel distance and size of each axis can be customized according to the application. Its reach and payload are independent rather than intertwined. Linear axes come in various designs to further adapt to the functions they perform.
The primary limitation of Cartesian robots is their comparative inflexibility. They easily adapt to linear movements across three axes and rotation around a fourth axis. However, an additional motion controller must be added to execute rotations around multiple axes. Cartesian robots are rarely used in washdown situations because they do not provide sufficient waterproof protection. Moreover, installation requires precision and thoroughness—each axis must be carefully aligned, and surface flatness must be adequate, especially in larger systems.
SCARA Robots
SCARA robots are designed for lightweight applications. They are streamlined versions of articulated robots, with simplicity and compact size making them easy to integrate into assembly lines. SCARA robots achieve considerable cycle times with high precision. They excel at inserting components into tight tolerances while maintaining rigidity during such movements, making them an economical choice for many pick-and-place applications and small part handling.
Delta Robots
Delta robots are known for their speed, capable of picking up to 300/min. Their overhead mounting minimizes the loss of floor space. They are often paired with vision systems to pick randomly placed parts in complex sorting and packaging applications. Like articulated and SCARA robots, they usually come with a teach pendant for ease of programming. Delta robots are commonly used in food production applications but may require additional shielding or isolation from the surrounding environment, similar to Cartesian robots.
Collaborative Robots (Cobots)
Cobots represent a relatively new development with promising potential in enabling safe human-robot interaction. By allowing direct collaboration between workers and robots, they add a dimension to our understanding of how automation can be integrated into industry. Cobots can be articulated, Cartesian, or SCARA types. They have payload capacities ranging from 4 to 35 kg, expanding their size and reach (and consequently price). Models with up to seven axes exist; the latter can perform particularly ergonomic tasks. Collaborative robots are even used as standalone line robots.
How to Choose a Robot
SPEED Packaging Equipment recommends considering all aspects of the application before making a final selection for a robotics investment. Here are some important factors to consider:
Reach and payload should be the primary criteria in your robot selection process, as these factors can immediately narrow down the list of suitable options. For example, large and heavy loads will rule out consideration of any lightweight handling technologies. On the other hand, if the distance is long but the payload weight is low, a less expensive Cartesian robot might suffice.
Robot Flexibility: In applications requiring five or six degrees of freedom, articulated robots may be the only viable solution. If so, one option for cost-sensitive enterprises needing one or two robots could be repurposed units. However, for simpler applications like small part positioning and loading, electronic component insertion, and box and machine tool loading—any application requiring just two or three axes—why pay for more axes than the application demands?
Robot Speed: Does the application require high pick rates, such as those provided by delta robots, or would lower pick rates from Cartesian gantries or SCARA robots suffice?
Robot Space and Footprint: Machine and production line footprints are becoming increasingly critical planning issues. Floor space is expensive, and companies want to optimize their shop floor layouts. Cartesian robots offer a distinct advantage over other technologies since only vertical space is lost, which is generally less critical.
Robot Engineering and Project Development: Design, assembly, installation, and commissioning time and costs should be factored into comparative costs, especially when integrating robots into larger machines or systems. Delays in receiving and assembling robots can delay entire projects.
Robot Maintainability, Repairability, and Availability: Unplanned downtime is every production manager's nightmare. Robots should be relatively easy to maintain and repair.
The proliferation of robotics has made automation benefits accessible to businesses of all sizes. The best robot for you is usually the one that best fits your application—not only in terms of productivity gains and meeting technical requirements but also from perspectives such as factory safety, space utilization, and, of course, initial costs and after-sales support.