All engineered systems follow a recognized pattern of failure known as the 'bathtub curve'
The timescale for this curve is typically 10-20 years for electronics and 1-5 years for mechanical systems depending on stresses and the purpose of the system. A car, for example, might be expected to show signs of wear after, say 60,000 miles which at an average of 30 mph is only 2000 hours or about 3 months of continuous use. A machine in a production environment might be expected to work 3 shifts a day for, say 2 years before showing signs of wear which would be about 12,000 hours.
It is in the early part of a system's life things are more likely to go wrong. This period is often referred to as infant mortality. Next comes a period of steady but low rate of failure which is usually quantified by MTBF - mean time between failures. The MTBF of an ST robot is approximately 20,000 hours. Finally things begin to wear out (senility). Failure rates begin to gradually increase. The system can continue to be used but will require frequent maintenance and replacement parts.
What sets ST robots apart from the startups
Keep it simple
Has been our mantra since the day we started.
From 'The Emperor's Old Clothes' by C.A.R.Hoare: "there is one quality that cannot be purchased and that is reliability. The price of reliability is the pursuit of the utmost simplicity."
On the left is the workings of a well known robot arm. On the right is the workings of an ST R12 robot arm.
These are the rules for total reliability:
- Keep electronics in the controller and out of the arm. Apart from being more reliable it means the arm can be used in hazardous environments, for example nuclear or wet environments. Once the covers are on and the ambient goes over 30C it's harder to get rid of the heat and much harder to meet EMC regulations such as FCC with RFI all over the robot.
- Don't use connectors. They are less reliable than the parts you might want to quickly replace and we long ago stopped using them, preferring direct wiring. There are no connectors in an ST arm.
- Copper wires do not flex indefinitely; they eventually fatigue and break. So we keep the wiring under control and free to bend around axis joints.
- Keep the gearing simple. ST's steel reinforced polyurethane toothed belts outlast gearboxes and are easy to replace.
- Keep Microsoft out of your robot. Windows is great for computers but robot software should be embedded and flashed, and, again, simple. Windows is not simple.
- ST's RoboForth software is simple and intuitive. It doesn't crash and programs in memory run indefinitely. You don't need to learn Python or ROS. You can use those tools if you wish but you don't need to. The PC is not controlling the robot; it is only there to help with programming. Take it away and save the cost.
- ST uses MicroChip 'Superflash', flash memory that can be over-written millions of times and outlasts any SSD
All the above is the result of decades of experience with real industrial and laboratory applications.
Keep it safe
So many robot companies show their robot bumping into a person and then stopping. That is totally unacceptable. ST have:
- Optional IR sensors that stop the robot when a hand intrudes into the workspace, stopping it before it hits the human being.
- Optional proximity sensors that will stop the robot if a human even gets near to it (or it near to them).
- Optional voice control: say "stop" and the robot stops.