This article is about using rotary torque sensors to measure torque during the torque verification and auditing process. But first, let’s talk football. Recently, a professional field goal kicker blew an easy shot. It was his second in the game and his fifth in two weeks. You can call it coincidence or cause-and-effect, but his team went on to lose both games. Nevertheless, his coach expressed absolute confidence in his wayward player. When asked why he thought his coach was so confident, the kicker replied, “Well, I don’t know what’s happening out here, but I’m nailing every kick I try in practice.”
It doesn’t take a professional athlete to know that practice is not the same as a game, just as it doesn’t take an engineer to know that conditions in the field or on the factory floor are different than they are in the lab. The only way to know for sure that something is going to work on game day is to try it on game day. So, if you’re missing a lot of field goals—or have a higher than comfortable rate of lost product—then it’s time to ask, why does my expected performance not match my actual performance? One common answer: the real thing isn’t the same as the test. Which returns us to rotary torque sensors and the role they play in reducing lost product due to fastening errors.
Rotary Torque Sensors vs. Static Torque Testers
First: what is a rotary torque sensor? It’s an instrument that quickly attaches to a power tool’s drive without interfering with the tool’s ability to fasten a screw or bolt. As the tool’s operator, whether human or robotic, tightens the fastener, the rotary torque sensor detects how much torque is applied until the tool shuts off and torque is applied to the fastener. That designated torque value is static. What the sensor measures is how much work it takes to get there.
These sensors are different from normal torque testers. When testing the torque output of a power tool on a normal torque tester, you will usually need a run down adapter to serve as a joint simulator. With these instruments, you can measure a power tool’s performance and repeatability. However, a power tool’s torque output on an actual fastening joint may or may not be different than its output in a controlled environment like a calibration lab. After all, a power tool’s torque is dynamic; various factors can impact the actual torque, like a soft rubber gasket or a plastic component. By connecting a rotary torque sensor to an electric or pneumatic tool and assembly application, you can accurately verify the torque being applied to the fastener or bolt and adjust the tool’s settings based on the audit results.
Rotary Torque Sensors Improve Quality By Measuring Torque During Application
The difference is the joint. Kicking on game day—with wind, roaring fans, pounding adrenaline, and an opposing team rushing towards you—is different from a calm practice kick. Similarly, applying torque on an actual joint—with washers, gaskets, lubricant, residue and even temperature related expansion or contraction to account for—is different from applying torque on a tester. There’s a separate set of conditions which require a small, but not negligible, adjustment in the amount of force delivered.
For fasteners with tight tolerances, that small difference can be enough to throw off production. Fasteners that don’t receive enough torque can fail to hold and back out. Fasteners that receive too much torque can warp or deform under stress, possibly damaging the assembly that holds them. Either scenario can cause further issues in assemblies with complex sequences, where each fastener depends on other ones to hold correctly.
So, if you’re testing your tools and they’re indicating that they’re in alignment but you’re still detecting repeated fastener errors during the quality control phase, the issue might be your testing regimen. Failing to account for actual joint conditions can create enough of a difference between expected and actual torque delivery that it affects your rate of lost product. To correct this, try using rotary torque sensors to measure torque as it’s applied to the actual joint you’re fastening. It should go without saying—if you can’t kick a goal in the game, then you can’t kick a goal.
