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Google "underactuated"
[1]: http://underactuated.csail.mit.edu/underactuated.html
[2]: https://www.edx.org/course/underactuated-robotics-mitx-6-832...
For more generalized information on how you bring a machine from state A to state B, you may want to read up on Control Systems [0], one of which is the PID controller [1]. It's used in everything from industrial water heaters to quadcopters. It wouldn't surprise me to see them also being used at some level with more advanced robotics. [0] https://en.wikipedia.org/wiki/Control_system [1] https://en.wikipedia.org/wiki…
PID is a generalized control algorithm that performs poorly unless your system is entirely linear. It is overwhelmingly used in industry, however, because it is simple, and anyone can drop in a PID block and adjust three constants to get semi-OK response without understanding anything about the dynamics of the system they are controlling. For serious control systems you can look up state feedback control, model predi…
Earlier quoted context omitted.
PID is a generalized control algorithm that performs poorly unless your system is entirely linear. It is overwhelmingly used in industry, however, because it is simple, and anyone can drop in a PID block and adjust three constants to get semi-OK response without understanding anything about the dynamics of the system they are controlling. For serious control systems you can look up state feedback control, model predi…
Yes, and I'm compelled to add that robots are typically actuated by servo motors and/or hydraulics, which are very commonly under the control of PID loops. Those PID loops allow the actuators to reach their set-points (whether position, velocity, etc.). To obtain 'smooth' motion, those set-points are usually streamed to the actuator at 60+ Hz, and it is the generation of those set-points that can become very complex;…
The industry standard update rate for servo systems is ~1kHz (although it depends on the application), and I have seen systems with >5kHz torque bandwidths. The torque dynamics associated with a typical PM machine used for servo systems are easily in the 10's or 100's of microseconds, so 60Hz control would not cut it.
Earlier quoted context omitted.
Yes, and I'm compelled to add that robots are typically actuated by servo motors and/or hydraulics, which are very commonly under the control of PID loops. Those PID loops allow the actuators to reach their set-points (whether position, velocity, etc.). To obtain 'smooth' motion, those set-points are usually streamed to the actuator at 60+ Hz, and it is the generation of those set-points that can become very complex;…
PID control is rarely used for professional servo applications, with the exception being amateur and lower performance systems (radio controlled, etc). This is especially true with PM servo motors because these machines are inherently nonlinear and cross-coupled. PID doesn't deal with either of these issues (nonlinearity or cross coupling) and therefore offers extremely limited performance. The industry standard upda…
For example, KUKA robot arms can operate in a mode where a motion path is planned and a sensor on a tool tip can make slight adjustments to the motion path on the fly. The points on those motion paths (as well as corrections) are updated every 4 or 12ms (83.3 to 250 Hz).
My point is that servo motor drives do indeed implement (sophisticated) PID controllers for current, position, velocity control loops. (2)
Obligatory Defensive Writing:
(1) Typical industrial servo motors implement sophisticated control over the velocity and acceleration profiles of the point to point moves. Anyone interested can look up the DS402 standard and take a look at the motion profile modes of operation.
(2) The PID loops implemented in servo drives are way more sophisticated than the canonical PID control loop equation (https://en.wikipedia.org/wiki/PID_controller). Nonetheless anyone who finds themselves manually tuning the servo loops for an industrial servo motor will surely find themselves setting proportional and integral gains.
Source: Commissioning servo motor drives is a part of my job.
Here's a good paper on RL in robotics: http://www.ias.tu-darmstadt.de/uploads/Publications/Kober_IJ...
RL is not widely used for control, but it has yielded some impressive results. In my experience I had a highly dynamic system for which I built a hand-tuned model for motion planning. I also built a RL model and trained it using the hand-tuned model. The RL model performed more than 50% better than my very best efforts.
Also, some of my favorite textbooks:
Principles of Robot Motion by Choset et. al.
Statistical Robotics by Fox, Burgard, and Thrun
Linear Systems Theory by Hespanha
http://homes.cs.washington.edu/~todorov/
He's done some amazing work recently in helping solve problems surrounding movement planning (not really the same as path planning like A*), so you can tell a robot to do something general like "stand here", and it treats the movement planning as an optimization problem and the dynamics of its 'body' and physics as constraints. The resulting behavior is eerily lifelike.
Earlier quoted context omitted.
PID control is rarely used for professional servo applications, with the exception being amateur and lower performance systems (radio controlled, etc). This is especially true with PM servo motors because these machines are inherently nonlinear and cross-coupled. PID doesn't deal with either of these issues (nonlinearity or cross coupling) and therefore offers extremely limited performance. The industry standard upda…
Again, yes, but to clarify, the 60+ Hz I was referring to was not the servo loop update rate, but the rate at which (loosely speaking) the servo loop setpoint is updated. (1) For example, KUKA robot arms can operate in a mode where a motion path is planned and a sensor on a tool tip can make slight adjustments to the motion path on the fly. The points on those motion paths (as well as corrections) are updated every 4…
I'm not just being pedantic here, there is a world of difference between a modern servo controller and a simple (or advanced) PID controller. Good servo controllers include completely different topologies including state feedback decoupling, disturbance decoupling, state tracking feedforward terms, advanced notch filters, sliding mode gains, and many other techniques. This is not just an advanced PID loop, but a different controller design method altogether.
Source: I design servo (and other motor) controllers for a living
Here's a recent paper using one of these approaches: http://www.intechopen.com/books/international_journal_of_adv...
One approach that could be used for a system like Big Dog would be a feed-forward control loop with kinematic/dynamic modelling of the robot. These approaches use knowledge of the system dynamics to predict the output based on changing inputs or disturbances.
You say you're not interested in path planning, but path planning and control are really on the same spectrum, which is motion planning. For instance, where to next put big dog's leg is a control problem, but also a path planning problem (how do I get the leg there? Where is the best place to put the leg? Does the leg collide with anything?). If you can't answer these questions and are blindly putting your leg wherev…
"Planning Algorithms" by Steven M. LaValle
>This book presents a unified treatment of many different kinds of planning algorithms. The subject lies at the crossroads between robotics, control theory, artificial intelligence, algorithms, and computer graphics. The particular subjects covered include motion planning, discrete planning, planning under uncertainty, sensor-based planning, visibility, decision-theoretic planning, game theory, information spaces, reinforcement learning, nonlinear systems, trajectory planning, nonholonomic planning, and kinodynamic planning.