What is a 7-axis robot arm (and when is it used)?

Introducing the 7-axis robot arm

A 7-axis robot arm gives an extra degree of flexibility and skill compared to the more common 6-axis designs. These arms have an extra rotational axis that allows the robot to move and pivot sideways. 

This sideways motion allows for even more human-like movement and manipulation. (It’s important to note that we’ve got a way to go before we achieve fine motor control of the human arm.) 

A 7-axis robot arm’s special strengths include:

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• Wrist rolls: The ability to rotate the end-effector (gripper or tool) around its own axis, similar to how a human wrist can twist. This is useful for tasks like screwing, unscrewing, or adjusting the orientation of objects.
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• Arm redundancy: The extra axis can be used to achieve the same position and orientation of the end-effector in multiple ways. This is called redundancy and is useful for obstacle avoidance or maintaining a specific wrist orientation while maneuvering in tight spaces.
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A 7-axis robot arm has seven axes, which can be a combination of rotary and linear axes (depending on the manufacturer).

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Components of a 7-axis robot arm

In a 7-axis arm, the seven joints usually consist of a base, shoulder, elbow, wrist, and end-effector. 

Let’s explore this a bit deeper: 

• The base gives support and allows the arm to rotate. 
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• The shoulder, elbow, and wrist joints give the arm a wide range of motion. 
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• Finally, the end-effector, like a gripper or welding tool, interacts with the environment.
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Some 7-axis arms also have an extra joint for the end-effector for even finer control. The high number of joints allows these arms to access confined spaces and awkward angles that would be difficult or impossible for humans — or robots with fewer degrees of freedom. 

The extra joint also provides redundancy so that if one joint fails, the arm can still operate, albeit with reduced capability.

The joints are powered by actuators, like motors, that are controlled by a computer. 

Sophisticated software coordinates the movements of each joint to guide the end-effector through a series of complex maneuvers. 

Additionally, some robot arms use gears and pulleys to transfer power from the actuators to the joints, while others use a cable drive system for smoother, more responsive movement.

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How a 7th-axis robot arm works

The seventh axis of rotation allows a robot arm to pivot sideways in addition to the standard up/down and left/right movements. 

This means it can bend, twist, and reach in ways that other robot arms just can’t. 

The 7th axis is basically a track or platform on which the robot arm sits (or sometimes an extra joint on the arm itself). This track can move back and forth, side to side, or even rotate, giving the arm a much larger working area and allowing it to reach places it couldn't before. 

This extra flexibility makes 7-axis robot arms perfect for jobs that require some serious maneuvering.

These additional capabilities give 7-axis robots greater flexibility, allowing them to perform tasks that are difficult or impossible for 6-axis robots. 

For example:

• Reaching around obstacles: The additional wrist roll and redundancy allow a 7-axis robot to reach around objects or into tight spaces where a 6-axis robot might collide or be unable to maneuver.
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• Maintaining tool orientation: In some applications, it's important to maintain the orientation of a tool (e.g., a welding torch) while moving the robot arm. The extra axis can be used to adjust the wrist roll to compensate for changes in arm position, ensuring consistent tool orientation.
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Performing complex assembly tasks: The increased flexibility and dexterity of a 7-axis robot can be advantageous for assembly tasks requiring precise positioning and manipulation of components in tight spaces or at awkward angles.

Comparison with other multi-axis robot arms

Here, we’ll take a look at how 7-axis robot arms stack up against other types: 

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Let’s take a look: 

• 6-axis robot arms: Great for welding, painting, and moving stuff around, but they can't twist and turn like a 7-axis arm can, so they struggle in tight spaces or with fancy moves.
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• SCARA robots: These guys are lightning-fast at picking and placing things, but they aren't as flexible as 7-axis arms when it comes to complex assembly or welding.
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• Delta robots: They're super speedy and accurate at picking and placing, but they lack the ability to move around obstacles or perform tasks that require bending and twisting.
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• Cartesian robots: Perfect for doing the same thing over and over, like moving stuff in a straight line, but they can't handle the complex, multi-directional movements that 7-axis arms are capable of.
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• Collaborative robots: They're built to work safely alongside people, but they often sacrifice speed, strength, and the ability to perform complex movements that 7-axis arms excel at.

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Advantages of using a 7-axis robot arm

A 7-axis robot arm offers quite a few advantages, especially compared to other robot arms: 

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• An extra level of skill. With seven joints, these robot arms have a greater range of motion and ability to manipulate objects in tight spaces. If you have an application that needs an arm that moves flexibly with the best of ‘em, then 7-axis robots are for you. 
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• More precise. The extra joints provide more points of control, allowing for very precise, accurate movements. 7-axis robot arms can position objects with submillimeter precision, performing delicate procedures like micro-assembly, soldering, and parts inspection. Of course, so can 6-axis arms (and others), so it all depends on your chosen application. 
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• They can reach into tight spaces. The articulated design and slender profile of 7-axis robot arms allow them to access confined areas that would otherwise be difficult, or outright impossible, for humans to reach. They can snake into tight spaces, around corners, and in between obstacles. 
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• Reduced setup times. With their extensive range of motion, 7-axis robot arms require less repositioning and reprogramming to access different areas of a workspace. They can typically reach any point within their operating envelope without you needing to move them or alter their position. Of course, this is provided they’re programmed correctly — a big if.

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Common applications of 7-axis robot arms

You’ll find 7-axis robot arms hard at work across many industries and tasks. 

Let’s take a look at some examples: 

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High-precision assembly

Delicate precision assembly requires a high level of control and articulation that 7-axis robot arms can provide. 

They’re often seen assembling small electronic components, medical devices, or other high-precision parts where accuracy and repeatability are essential.

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Welding

In welding, 7-axis robot arms give operators more control over the welding torch or laser. Their additional joint allows for better positioning and manipulation, especially in confined spaces or at awkward angles. 

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Painting

In the auto industry, 7-axis robots are frequently used for complex painting jobs like applying primer, basecoat, and clear coat. 

Their skills provide exceptional mobility and access to hard-to-reach areas. They can also handle multiple paint guns or other tools for even more efficiency.

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Challenges and considerations in using 7-axis robot arms

Of course, before you go ahead and purchase a 7-axis robot arm, you’ll have to think about the potential challenges:

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• They can be hard to program. The more joints and axes a robot has, the more difficult it is to program precise and smooth movements. It takes skilled programmers and lots of testing to ensure the arm moves efficiently without collisions or errors.
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• Not on the cheap end. 7-axis robot arms are more expensive than simpler multi-axis arms, both in upfront costs as well as maintenance over time. The arms themselves cost more to produce, and they require advanced control systems and software to operate. You’ll also need highly-trained personnel to program and oversee the robots, which can make costs add up.
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• Limited workspace. While 7-axis arms have greater flexibility and skill, their complex design limits the size of the workspace. They typically have a smaller range of motion than simpler arms. 
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• Higher energy consumption. The advanced components and increased power needed to control a 7-axis arm result in higher energy usage overall. If you have a large-scale operation with many robots, energy costs can be substantial. Advancements in motor technology and energy efficiency can mitigate this issue, though.
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• Increased need for downtime. With more joints and parts comes a higher chance of technical issues that can cause downtime. While well-designed 7-axis robots are generally reliable, malfunctions do occur, and repairs often take longer than with simpler arms.

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Summing up

Those were the ins and outs of the 7-axis robot arm.

With the fact that the 7th axis is such a powerful component that helps in very intricate, minute tasks, it’s no surprise that these robots come with a higher price tag than average. 

But, of course, if your application doesn’t require complicated twists and turns straight out of an advanced yoga program, then it’s highly likely that you’ll be just fine with fewer planes of motion.

As always, carefully consider your application and then make an informed decision. More axes are not always necessary. 

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Next steps 

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