One of the challenges of many walking robot designs is the fact that they draw current just to stay upright. This was exactly the case for one [James Bruton]’s quadruped robots, where the knee motors were getting too hot to touch. Adding springs to take some of the load is not as simple it might seem, so [James] created a bungee assisted cam mechanism to do the job.
For a normal spring-loaded lever, force is proportional to how much the spring is stretched, which will require the actuators to draw more and more current as it lifts the leg higher. For the spring force to remain constant throughout the range of motion, the length of the lever arm must become continuously shorter as the knee is bent. [James] did this by stretching a bungee cord around a cam. The added bulk of the cam does however cause the knees to knock into each other in some scenarios, but [James] plans to adjust the robot’s gait to avoid this. He didn’t get around to actually measuring the current draw reduction, but the motor temperature has dropped significantly, only being slightly warm after a test run.
These tests were done with OpenDog V2, but [James] is already working on the design of V3, which will use 3D printed cycloidal gearboxes. At the moment, that build is still being delayed thanks to the global component shortage. Continue reading “Bungee And Cam Assisted Actuator For OpenDog”
Sony’s video game division is gearing up for their upcoming PlayStation 5, pushing its predecessor PlayStation 4 off the spotlit pedestal. One effect of this change is Sony ever so slightly relaxing secrecy surrounding the PS4, allowing [Nikkei Asian Review] inside a PlayStation 4 final assembly line.
This article was written to support Sony and PlayStation branding for a general audience, thus technical details are few and far in between. This shouldn’t be a huge surprise given how details of mass production can be a competitive advantage and usually kept as trade secrets by people who knew to keep their mouths shut. Even so, we get a few interesting details accompanied by many quality pictures. Giving us a glimpse into an area that was formerly off-limits to many Sony employees never mind external cameras.
The quoted engineers are proud of their success coaxing robots to assemble soft and flexible objects, and rightly so. Generally speaking robots have a hard time handling non-rigid objects, but this team has found ways to let their robots handle the trickier parts of PS4 assembly. Pick up wiring bundles and flat ribbon cables, then plug them into circuit board connectors with appropriate force. Today’s automated process is the result of a lot of engineers continually evolving and refining the system. The assembly machines are covered with signs of those minds at work. From sharpie markers designating positive and negative travel directions for an axis, to reminders written on Post-It notes, to assembly jig parts showing the distinct layer lines of 3D printing.
We love seeing the result of all that hard work, but lament the many interesting stories still untold. We would have loved a video showing the robots in action. For that, the record holder is still Valve who provided an awesome look at the assembly of the Steam Controller that included a timelapse of the assembly line itself being assembled. If you missed that the first time, around, go watch it right now!
At least we know how to start with the foundations: everything we see on this PS4 assembly line is bolted to an aluminum extrusion big or small. These building blocks are useful whether we are building a personal project or a video console final assembly line, so we’ve looked into how they are made and how to combine them with 3D printing for ultimate versatility.
While robotic arms can handle a wide variety of tasks, the specific job at hand will have a major influence on the type of end effector used. For sorting ferromagnetic parts an electromagnet might be enough, while for more accurate location a mechanical gripper could be employed. If you’re working with particularly delicate objects or in concert with human beings, it may be desired to have a force controlled gripper to avoid damage. [James Bruton] has been whipping up a design of his own for just this purpose.
The basic gripper is 3D printed, with 3 fingers consisting of two joints each. Retraction of each finger is courtesy of bungee cord, while extension is via a servo attached to the finger through a spring. The position of each finger is measured with a resistive flex sensor. An Arduino Uno is employed to run the servos and read the attached sensors.
As force is applied by the servo, the spring begins to stretch. This leads to a greater difference between the servo position and the finger position as the applied force increases. By calculating this difference, it’s possible to determine the force applied by the fingers. This can then be used to limit the applied force of the gripper, to avoid breaking delicate objects or crushing soft, fleshy humans.
[James] notes that there are some drawbacks to the current design. The force required to move the fingers is inconsistent along their travel, and this interferes somewhat with accurate measurement. Overall though it’s a solid proof of concept and a good base for further revisions. Files are on Github for those who wish to tinker at home.
Being aware of the forces applied in mechanical settings can be key to getting good results. We’ve even seen arbor presses modified for just such a purpose. Video after the break.
Continue reading “This Force Controlled Robot Gripper Is Less Likely To Break Stuff”