With this lecture, we are shifting into the mechanical system and take a look at the motion mechanical subsystem that governs how a 3D printer physically executes the instructions for how and where to deposit materials delivered to it by the electronics control board. What is the mechanical system? As I mentioned before, the mechanical system groups everything to do with not only motion, but the frame on which everything is mounted, and when applicable, the enclosure that shields machine from the surrounding environment. The role of the mechanical system is to move everything that needs to move, deliver it where it needs to get there, when it needs to get there, and report back when necessary that this movement is complete. The extrusion system manages everything to do with moving and liquefying the printable material. But remember that this effort would not be valuable at the end of the day if the material squirting out of the nozzle didn't make its way onto the build plate. These two systems need to coordinate their activity together for the magic to happen. Thus, the critical aspect of the mechanical system is to establish the physical constraints of the build envelope, the 3D printing construction volume of the printer, and everything to do with making sure that the machine, in particular the physical hot end in the extrusion system, can address every aspect of that build envelope to build the printed part. So for the steady hand with the hot glue gun, the circling cup to receive the soft-served ice cream, we have the mechanical system to thank. The mechanical system gets a lot of attention. It is after all the first thing new visitors notice when confronted with a printing desktop unit, the parts that are moving, and the decisions that printer manufacturers make in this area play a central role in categorizing the machine. A Cartesian machine versus a Delta machine, even when those decisions play only a marginal role in what sort of printed parts can be produced by each type. But we find that to really understand why there is a wide variety of machine design approaches in this area, it is worth taking you through a high-level overview of the mechanical system key subsystems and components in order to place them into a context so that the roles for each are clear. Given how easy it is to get lost in the weeds with the terms associated with the various separate mechanism decisions here, we're going to walk you through a shell diagram that I find helpful. Machine origin point. So we start here in the middle of the build plate, the very heart of the entire mechanism. This isn't a physical component, but a position that the machine recognizes and it performs all of its 3D printed part construction activities in terms of this position. We will call this point the origin point, the 000 position on an XYZ Cartesian plane, although there is a similar origin point no matter which coordinate system or machine design type you use. The moment this value is established in terms of the control electronics, the mechanical system, and the extrusion system, then it is possible for the machine to coordinate the activity of printing a physical object. In practice, many machine designers for Cartesian style machines, the most common type, will put the origin in the bottom front left corner to eliminate the need for negative values in X, Y, and Z. Coordinate system. Before we can move outwards to the next shell, before the machine can move in any way at all actually, there must be an established coordinate system for the machine. The machine origin point plants a flag in the build envelope that says this is 000, but all actions that make use of this value to actually do any work need to create on the coordinate system that governs in which direction and via what type of movement you increment those numbers. 3D printed object moving out one more shell. We have the 3D printed object itself. This is the whole point of the machine, where everything in the control, mechanical, and extrusion system come together to squirt liquefied plastic into the right places following the right sequence so that the resulting part will be what the operator intended. It is important that you don't forget how important it is for the machine to correctly map the virtual origin point to the correct physical position within the machine. That way, it can be acted on in concert between the three systems. Then when the activity printing begins and the extruder nozzle is moving through all the positions assigned to the 3D printing object itself, these three systems might indeed each falter on instructions but in a way that the part you'd like to create is actually created as intended, unless you're looking for messy 3D printed birds' nests and broken machines. Build envelope. Let's move out another shell. Now we have what is called the build envelope. This is the construction zone for the printer, the larger virtual space that includes every point that is possible for the nozzle to move through while extruding plastic. Looking back to the 3D printed object. Every position the nozzle must pass through to produce the printed object again in terms at origin position must be contained within the build envelope, or else producing the part would not be possible. Build plate. The physical platform where the printing takes place is typically called the build plate or build platform. We'll talk about build surfaces, films, glues, and the critical process of maintaining good print adhesion later when it comes up in the extrusion system. But for now, let's just focus on the mechanical aspects of this component. This is the build plane upon which the 3D printed part will be constructed. Thus, the entire build envelope sits on top of it. Typically, the build volume is slightly smaller than the build platform to avoid areas like the very edge of the heated build platform, where there might be issues with temperature or physical obstacles that could create problems. Likewise, the establishing of the origin point when printing needs to position the build envelope as high enough above the surface of the platform that the nozzle doesn't collide with a platform and so that there is room for squirting out the first layers. Motion mechanical subsystem. Moving out another shell, we are in the prime territory for the motion mechanical subsystem itself. Thinking in terms of this shell diagram, the motion mechanical system consists of everything that is necessary for the machine to address all of those deeper shells inside. It needs to play its role in establishing the exact origin point that allows the machine to map the instructions in the job file, manage the physical positions within the build area. It needs to be able to deliver the toolhead carriage to every point within the 3D printed part design file the same way for consistent results every time you print. Decisions for how to construct the machine, shape the build envelope, the available territory for printing, and the position and motion, if there is any, of the build plate and toolhead carriage should be managed for consistent printing results in terms of a clear positional relationship between each other. That probably includes movement of the toolhead or other elements through territory beyond what is addressable for printing, including such techniques as homing the machine or changing a toolhead. So then what does the motion mechanical subsystem look like? There's actually a lot of variety for how to solve the mechanical challenges to meet these needs successfully, and we will look at several of them in greater detail. Frame case enclosure. While a great deal of the complexity of the mechanism can be found in the territory of the motion mechanical system, there are shells outside that as well. The frame is the structure upon which all of the components are mounted. This frame plays a key role within the motion mechanical subsystem because it constrains the scale and position options and provides a firm anchoring system that allows the motion mechanical subsystem to do its work. Widening to another shell beyond the frame, we have the case. This element includes both the inside coverings and housing elements that can conceal and protect functional elements, cabling, and electronics that shouldn't be exposed, as well as the outside coverings and casing elements that protect delicate elements on the outside of the machine frame, protect the machine itself, and also for machines that enclose or partially enclose help to contain heat and dry conditions and to baffle breezes and other outside interference that might cause issues when printing. The final shell extends beyond the machine itself. 3D printer enclosures are meant to surround and protect the entire machine and its functional elements. Typically as a measure, either to protect the machine from drafts and reduce the amount of heat and power, to keep the printing area warm, or to isolate the printing process and/or fumes and particles from those in the area around the printer or both. Now that we have gone through the entire sequence, from the origin point all the way out to the outer enclosure, hopefully the roles for each of these elements is much more clear setting the stage for us to explore each of these elements in greater detail in the lectures to follow.
