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Point Test 1

Robots Repeatability, what is it and how does HEW compare?

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Making a robot that is accurate and repeatable is key aspect of any robot arm. That’s why our robot HEW is designed around all metal gear, high torque digital servos. Motors are the heart of any robot, but what good are motors if your accuracy or repeatability doesn’t add up.

In this blog update I’ll be going through, what accuracy and repeatability mean for robots, what the difference is between the two and how we tested HEW.


So what is accuracy and repeatability?

Simply put they are both measurable characteristics of how a robot can and does perform during its use and as such a robot would be useless if they didn’t go to where they were programmed too. An excellent example is Kuka’s own robot arm the KR 16 ARC HW which has very high accuracy with a repeatability value of +/- 0.05mm (The accuracy value isn’t shown however, as robots use feedback on each motor to ensure each is at the exact desired point).

A robots accuracy is how well it can reach the target destination with minimal error, for example if your using a spot welding robot (most often used in car production assembly lines) to weld panels together with a set point to be welded, you want the robot to go to that same point every time, so that the weld is always in the exact same spot. This is what make robots great for autonomous production as their accuracy combined with their flexibility gives them a large range of applications that are also flexible as the robot can be moved and reprogrammed to do another task, such as a shot peening process used in the aerospace sector (a process using metal shots (balls) to create a compressive layer in metals).

Repeatability is somewhat similar to accuracy and can sometimes be mistaken for it. The repeatability is how well the robot can reach the exact same point every time within a given distance often stated in millimetres (mm), sometimes called ‘grouping’. For instance let’s say our accuracy is perfect but our repeatability is +/- 1mm, this means that at the target point X the robot will always be within a 1mm radius of point X.


What is the difference of accuracy and repeatability?

As we spoke about before accuracy is the distance between its target destination and where it’s actual position is,

Whereas repeatability is how far from its actual position it will be every time it goes to its target destination, in essence it how consistent your robot actually is.

Robots repeatability and accuracy

Image source:

A good way to think of it is, imagine you are firing an air rifle at a classic circular set of targets, your accuracy is how far away from your point of aim your bullet hit i.e. you aimed for the center but hit 5mm awas, and your repeatability is how well you can repeat that same shot every time, as such you have your aim (accuracy) versus consistency (repeatability).


How does HEW compare?

Like most robots our robot arm HEW also has these characteristics and we’ve tested them from the early prototypes during developments through to the final version HEW-DV4 and he stacks up quite well we think.

Point test 1

HEW-DV4 Point test: Repeatability test image sample

Overall HEW performed well during testing, with a high accuracy due to the fact that servos use a feedback loop to ensure they reach the same desired position, and with repeatability being no more than 3mm, we are very happy with HEW’s results. Overall it is a great spec for a desktop and better than we expected. One of the reasons these specs are so good is due to the fact we only use all official, high torque, metal gear servos (the counterfeits versions simply don’t compare) along with a good study design and solid base. Simple put good quality makes good robots!

Block test 2 Control shot

Repeatability: Testing block placement area

The above image shows the testing area which was created using a laser cutter and 10mm MDF, which would also be used to securely mount our robot HEW onto. The outlined box etched on by the laser cutter was the same size as the block to be used during testing with an additional 10 lines etched each side spaced 1mm apart for a maximum of 10mm either side (The laser cutter itself has a keft of 0.2mm so anything less than 1mm wouldn’t be practical to test). This gave us a test bed that was solid and accurate.

Now that we know how well HEW can perform all that is left to do now is to grab your self your own HEW desktop robot and make your own home automated tea maker, toaster, robot band, mini assembly line and more! His uses are endless who knows what you could do. Simply head over to our store pick your colour and kick-start your next project today. Whether you’re new to robots or an expert user, HEW is a great interactive tool for anyone to use.


A more in-depth and a great external Article from Robotiq can be found here:

Topics: Desktop robots, HEW-DV4, robot arms, accuracy, repeatability

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