Working as someone who’s spent the last 12 years supplying precision robot joints to manufacturers across automotive, logistics, and medical device sectors, I get asked a version of this question at least twice a month: If one joint on a robot arm fails, does the whole system grind to a halt? It’s a fair question—on a shop floor, a single part going wrong can cost thousands in downtime, so everyone wants to know how much risk they’re actually taking on. Robot Joint
I’ll start with a concrete example, because that’s what my engineering team and I rely on every day. Last quarter, we had a client in the Midwest who ran 12 6-axis collaborative robots (cobots) on their light assembly line. One of these cobots, assigned to tightening small bolts on electronic control units, developed a fault in its 5th joint—a harmonic drive that drives the wrist rotation. The joint’s encoder, which tracks the joint’s exact position, had a minor wiring misalignment that made it report a 1.2-degree offset. For most hobbyists or someone who only follows robot specs, that seems trivial. But on that assembly line, the 5th joint’s rotation is what aligns the cobot’s gripper with the bolt hole. A 1.2-degree offset meant the gripper missed the hole 30% of the time.
Here’s the thing: that robot didn’t just keep running. It ran for three full shifts before maintenance pulled it offline. Why? Because the cobot’s integrated control system isn’t programmed to stop at the first sign of a faulty joint—it’s built to compensate. But compensation isn’t a free fix, and that’s where the real answer to “can a robot function normally?” gets complicated.
Let’s break down how robot joints work, first, because you can’t answer the function question without understanding the parts I supply. Every industrial robot (cobot or traditional 6-axis) has between 6 and 10 joints, each with three core components: a motor, a gearbox (harmonic drive, planetary, or cycloidal, depending on the use case), and an encoder that gives real-time position data. As a joint supplier, we test every unit for backlash, positional accuracy, and load capacity to within 0.05 degrees, because that’s the threshold most robot control systems are calibrated to.
A single faulty joint doesn’t just break one part—it skews the entire robot’s kinematic chain. The kinematic chain is the set of mathematical calculations that tell the robot how to move from Point A to Point B. If Joint 3, for example, is supposed to rotate 90 degrees to move the arm forward, but instead rotates only 88 degrees because its gearbox has stripped teeth, the end effector (gripper, welder, suction cup) will be 20 millimeters off target. Control systems use inverse kinematics to adjust other joints to compensate, right? That’s the compensation I mentioned earlier. In the Midwest cobot case, the controller adjusted Joints 1, 2, and 4 to account for the 1.2-degree offset in Joint 5. It worked… sort of. But that compensation came with costs the line’s team didn’t anticipate.
First, speed. The compensation required the robot to slow its wrist movement by 40% to avoid overextending other joints, which added 12 seconds to each bolt tightening cycle. On an line that produced 2,000 units a shift, that meant 400 units missed their production targets that day. Second, load capacity. The faulty Joint 5, now working under duress because the controller was forcing it to make up for the encoder error, ran 28% hotter than its normal operating temperature. By the end of the third shift, the joint’s grease had thinned, adding extra friction and increasing wear on the gearbox. When maintenance finally replaced the joint, they found that the strain on it and the surrounding joints had caused minor surface damage to the adjacent 4th joint—damage that would have become a full failure in another two weeks.
So that’s function: the robot kept moving, it did the job (eventually), but it wasn’t functioning normally. “Normal” here isn’t just working—it’s working as intended: at design speed, with full load capacity, without risking secondary damage, and without falling short on quality. The question isn’t can it do something—it’s can it do what it was built to do.
Let’s look at a different scenario, one where a more severe joint fault plays out. A year ago, we supplied 8-axis joints for a palletizing robot at a national distribution center. The 6th joint, a planetary gear, had a sudden bearing failure mid-cycle. This joint is responsible for rotating the robot’s arm to stack pallets of 50-pound boxes. The control system tried to compensate, but a bearing failure isn’t a positional error—it’s a mechanical lock. The joint couldn’t rotate at all. The robot’s controller registered the fault within 0.2 seconds and shut the entire system down to avoid damaging the motor. That case was a total stop, but it’s important to note that this is the exception, not the rule—most partial joint failures are gradual, like the encoder misalignment or the gear wear I mentioned earlier.
What does industry data say about this? A 2022 study from the International Federation of Robotics (IFR) found that 68% of robot joint faults are slow-onset (wear, encoder drift, minor gear backlash) rather than sudden (bearing failure, complete motor burnout). For these slow-onset faults, 72% of robots will remain operational at reduced capacity, but only 19% maintain 90% or more of their design performance. That aligns perfectly with our own client data: over the last five years, our clients with robot fleets have reported that a single faulty joint cuts individual robot performance by an average of 32% before replacement is needed.
But here’s a nuance that most non-experts miss: not all robots are built the same. Collaborative robots, for example, are programmed for flexibility and safety, so their control systems are designed with more built-in compensation for minor errors. A cobot working in a small machine shop might keep operating at 80% capacity for weeks with a faulty joint, because its tasks are low-stakes and don’t require consistent precision. Traditional industrial robots, used for high-precision tasks like welding or electronics assembly, have much tighter positional tolerances—often ±0.1 millimeters. A faulty joint that causes even a 0.5-millimeter positional error will cause the robot to fail quality checks, so it will stop working entirely, even if the controller is trying to compensate.
As a joint supplier, we see this play out every time we work with a new client. A few months ago, a medical device manufacturer reached out because their robot used to assemble pacemaker circuits was failing 15% of the time due to a faulty rotary joint. The previous supplier’s joints had ±0.2-degree positional tolerance, which was enough to cause the robot to misalign the micro-sized circuit pins. When we replaced those joints with our own, which have ±0.03-degree tolerance, not only did the assembly error rate drop to 0.1%, but the robot was able to run at full speed even when one of the joints had a minor seasonal drift from temperature changes. That’s the difference that precision makes: a small fault in a higher-quality joint can be compensated for without a huge hit to performance, but the same fault in a lower-precision joint will bring the robot to a halt.
Another factor: the type of task the robot is performing. A robot doing simple pick-and-place for cardboard boxes is far more forgiving of a faulty joint than a robot doing laser welding on car frames. For pick-and-place, a 2-degree positional error might only mean the box is placed an inch off, which is easy for a human to fix. For laser welding, a 0.5-degree error can mean a bad weld that causes a car frame to fail a safety inspection. So the answer to “can it function normally?” is never universal—it depends on the robot’s design, the quality of its joints, and the task it’s assigned to do.
Let’s circle back to the original question, because I’ve given a lot of context but not a direct answer. A robot will keep moving, technically, with a single faulty joint—most of the time, for slow-onset faults. But it will not function normally. Normal function means meeting design specs: full speed, full load capacity, positional accuracy within tolerance, no secondary damage risk, and consistent output. A faulty joint introduces compromise: reduced speed, increased energy use, higher risk of further failure, and inconsistent quality. The only exception is if the robot’s task and design are so flexible that they can absorb the error without impacting performance, which is rare in most industrial settings.
As someone who’s spent decades engineering and supplying robot joints, my advice to every client is this: don’t wait for a fault to test your robot’s resilience. We offer fleet assessments that check joint tolerance levels, wear rates, and control system compensation capabilities, so you can spot a faulty joint before it causes downtime. A single joint replacement costs a fraction of the downtime, scrap, and secondary repairs that come with running a robot that’s operating at less than full capacity.
If you’re noticing inconsistencies in your robot’s performance, or if you want to learn more about how high-precision joints can reduce fault risk, we’re here to help. We work with clients across all industrial sectors, providing custom joint solutions tailored to their specific robot models and tasks, so you can keep your line running smoothly without the stress of unexpected faults.
Sheet Metal References
International Federation of Robotics. (2022). Joint Failure Patterns and Mitigation Strategies in Industrial Robot Fleets. IFR Technical Report Series.
Robotics Industries Association. (2021). Collaborative Robot Performance Under Partial Joint Fault Conditions. RIA Standards Publication.
Zhang, L., et al. (2020). Kinematic Compensation for Partial Joint Faults in 6-Axis Industrial Robots. Journal of Manufacturing Systems, Vol. 56, pp. 327-335.
Shenzhen Jingcheng Dingyi Forming Technology Co., Ltd.
Address: 1st Floor, Building 3, Huafeng Zhenbao Industrial Park, No.137 Shihuan Road, ShiYan Town, Bao’An District, ShenZhen, PRC
E-mail: 13071475061@163.com
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