The field of mechatronics has many interesting tangents. One of the most subtle, yet important aspects is the field of materials properties. The materials selected for use in actuators and machinery becomes a significant determinant in what the inertia load will be and even more importantly, how it will behave.
There are many properties of merit to the designer, and stiffness is one that should never be overlooked. Stiffness can be a valuable tool to use in making mechanisms that have high repeatability and operate at high speed. Sometimes the only way to solve throughput problems is to substitute titanium for steel. Titanium is much higher strength than steel and lower density so it has high great value in reducing inertia and retaining stiff response. But titanium is very expensive and difficult to machine. So this solution isn’t always econonical.
Interestingly, Aluminum is a very popular substitute for steel because it is one third the density of steel and machines very easily. This can result in parts that are actually lower cost and reduces the power required to operate the mechanism. But as speeds or acceleration requirements increase, the relatively soft aluminum can flex and lose critical position. This is one case of compliance. And if you have to do high speed registration, compliance can be a real problem.
But compliance is something we need to avoid shock load and premature mechanical failure in moving parts. Sprocket and chain drives can have compliance. Belt driven actuators have compliance. Motor couplings have compliance. And properly applied, compliance has great value.
But there are a lot of cases where compliance is present but not accounted for. Many roller transmissions claim to be zero backlash, but the very nature of the technology has some compliance in order to make it work. So as the load is starting and stopping there is some “flexing” or torsion that must be accounted for. In essence, there’s no free lunch. If there’s no backlash, there must be some other aspect of the design to account for.
So when is compliance a problem? Fortunately, not very often. Most systems that have compliance in them, it’s intentional. But there is a lot of technology where it’s not apparent.
In order to diagnose compliance problems, extra position feedback sensors on the load are needed. Particular attention needs to be paid to how precise it needs to be to measure the position error. The other key factor will be the minimum time needed to measure the position error. As system throughput increases the time available to measure the error decreases.
By measuring the error created by compliance, it can be controlled. Compliance can be an ally in making machinery that has more controlled starting and stopping of loads, which translates into quiet operation and longer operating life. Overall, a pretty good deal.