This is the third installment in what could be billed the "building series." The first two articles focused on rather involved fabrication techniques for larger robots; this time, I'd like to look at two more-accessible techniques for building miniature robots that I learned about at IROS 2009. The first technique, by Jessica Rajkowski and advisor Sarah Bergbreiter (et. al.) from University of Maryland, is a relatively new method employing multi-step photolithography via inkjet printed masks to build small polymer robots such as inchworms and grippers that are actuated by shape memory alloys (SMAs). The second technique examined is a bit more mature. Called "Smart Composite Microstructures" (SCM) and hailing from UC Berkeley's Biomimetic Millisystems Lab, this technique is used to build inexpensive, resilient, folded composite (cardboard, carbon fiber, fiberglass) prototypes with polymer hinges. Read on for details and videos.
The first technique comes from Prof. Sarah Bergbreiter's Micro Robotics Lab at the University of Maryland, and was presented at IROS 2009 in a paper entitled "A Multi-Material Milli-Robot Prototyping Process." The basic process is shown below.
First, a UV sensitive polymer (a Loctite photo-patternable adhesive) is laid down. An inkjet printed mask is used for UV photolithography, leaving behind a rigid (green) structure. A more flexible, soft silicone is then applied and photo-patterned in a similar manner to create flexible joints for the planar robot.
By embedding shape memory alloys (SMA) and control electronics, small robots can be created -- for example, the inchworms and grippers shown below.
Lead author, Jessica Rajkowski, was kind enough to share the IROS '09 video demonstrating the process.
The second technique is a bit more mature. It is called "Smart Composite Microstructures" (SCM) and hails from Ronald Fearings Biomimetic Millisystems Lab at UC Berkeley. The SCM process follows a few simple steps that essentially create a sandwich with rigid composites on the outside with flexible polymer inside. By controlling the location of the flexible polymer, the resulting structure can be folded into 3D forms and actuated. Consider these steps:
The drawing (1) shows the polymer-only regions (red) and the final composite cutouts (gray). First, the polymer locations are cut out (2) of the composite (cardboard, carbon fiber, or fiberglass) on a laser cutter. A polymer laminate (such as polyester) is glued between the two composites (3) and passed through a lamination machine (4) that applies pressure to bond the sandwich (5). The entire stackup is then cut on the laser cutter to produce the final robot pieces (6) that can be folded (7) to form a finished robot (8).
This process has been applied to build a number of hexapod walkers, actuated by either shape memory alloys or motors. I particularly like the look of the fiberglass variant on the right.
Anyway, this technique was recently used to build a robot named "Dash," that was presented at IROS 2009.
According to the paper, Dash weighs in at 16 grams, can run at 15 body lengths per second (1.5 meters/sec.), and has survive falls from 7.5 meters, 12 meters, and 28 meters! The video is particularly impressive.
In contrast to the more involved (expensive) fabrication techniques examined in the first two articles, I think these two examples demonstrate the feasibility of fabricating low-cost robots using relatively straight forward techniques.