Why not use PID controller? That's a good question. If the robot's joints are decouples and using PID controller for each joint is the way to go. All you need is model-free parameters that corresponds to each joint. In my case, I am simulating a humanoid robot with two arms, the joints and links are deeply coupled that model-free method does not work well here.
The Inverse Dynamics Controller is a system block that takes in the desired acceleration and spit out whatever the generalized control force is. Using Inverse Dynamics Controller is easy in Drake because MultibodyPlant does all the inverse dynamics calculation for you.
Code
Create a folder drake/examples/kuka_iiwa_arm_idc/
cd drake
mkdir -p examples/kuka_iiwa_arm_idc
Put the following file into the folder.
run_kuka_idc_demo.cc
/// @file
///
/// This demo sets up a kuka arm simulation.
/// An inverse dynamics controller was created to control the robot to
/// the desired system state.
#include <gflags/gflags.h>
#include "drake/common/drake_assert.h"
#include "drake/common/find_resource.h"
#include "drake/common/text_logging_gflags.h"
#include "drake/common/type_safe_index.h"
#include "drake/geometry/geometry_visualization.h"
#include "drake/geometry/scene_graph.h"
#include "drake/lcm/drake_lcm.h"
#include "drake/multibody/parsing/parser.h"
#include "drake/multibody/plant/multibody_plant.h"
#include "drake/multibody/tree/weld_joint.h"
#include "drake/systems/analysis/simulator.h"
#include "drake/systems/controllers/inverse_dynamics_controller.h"
#include "drake/systems/framework/diagram.h"
#include "drake/systems/framework/diagram_builder.h"
#include "drake/systems/primitives/constant_vector_source.h"
namespace drake {
namespace examples {
namespace kuka {
using drake::multibody::MultibodyPlant;
DEFINE_double(simulation_time, 5,
"Desired duration of the simulation in seconds");
DEFINE_double(max_time_step, 1.0e-3,
"Simulation time step used for integrator.");
DEFINE_double(target_realtime_rate, 1,
"Desired rate relative to real time. See documentation for "
"Simulator::set_target_realtime_rate() for details.");
DEFINE_bool(add_gravity, true,
"Indicator for whether terrestrial gravity"
" (9.81 m/s²) is included or not.");
DEFINE_double(Kp, 10.0, "Kp");
DEFINE_double(Ki, 0.1, "Ki");
DEFINE_double(Kd, 5.0, "Kd");
void DoMain() {
DRAKE_DEMAND(FLAGS_simulation_time > 0);
systems::DiagramBuilder<double> builder;
geometry::SceneGraph<double>& scene_graph =
*builder.AddSystem<geometry::SceneGraph>();
scene_graph.set_name("scene_graph");
MultibodyPlant<double>& plant =
*builder.AddSystem<MultibodyPlant>(FLAGS_max_time_step);
plant.RegisterAsSourceForSceneGraph(&scene_graph);
std::string full_name = FindResourceOrThrow(
"drake/manipulation/models/"
"iiwa_description/sdf/iiwa14_no_collision.sdf");
multibody::ModelInstanceIndex plant_index =
multibody::Parser(&plant).AddModelFromFile(full_name);
// Weld the hand to the world frame.
const auto& joint_arm_root = plant.GetBodyByName("iiwa_link_0");
plant.AddJoint<multibody::WeldJoint>("weld_arm", plant.world_body(), nullopt,
joint_arm_root, nullopt,
Isometry3<double>::Identity());
if (!FLAGS_add_gravity) {
plant.mutable_gravity_field().set_gravity_vector(Eigen::Vector3d::Zero());
}
// Now the model is complete.
plant.Finalize();
// Defind desired states, here we choose 0 positions and 0 velocities.
VectorX<double> desired_state =
VectorX<double>::Zero(plant.num_multibody_states());
auto desired_state_source =
builder.AddSystem<systems::ConstantVectorSource<double>>(desired_state);
desired_state_source->set_name("constant_source");
drake::log()->info(
"positions numbers: " + std::to_string(plant.num_positions()) +
", velocities numbers: " + std::to_string(plant.num_velocities()) +
", actuators numbers: " + std::to_string(plant.num_actuators()));
// Create inverse dynamics controller.
const int U = plant.num_actuators();
auto IDC =
builder
.AddSystem<systems::controllers::InverseDynamicsController<double>>(
plant, Eigen::VectorXd::Ones(U) * FLAGS_Kp,
Eigen::VectorXd::Ones(U) * FLAGS_Ki,
Eigen::VectorXd::Ones(U) * FLAGS_Kd, false);
builder.Connect(IDC->get_output_port_control(),
plant.get_applied_generalized_force_input_port());
builder.Connect(plant.get_state_output_port(),
IDC->get_input_port_estimated_state());
builder.Connect(desired_state_source->get_output_port(),
IDC->get_input_port_desired_state());
// Constant zero load for plant actuation_input_port.
auto constant_zero_torque =
builder.AddSystem<systems::ConstantVectorSource<double>>(
Eigen::VectorXd::Zero(plant.num_actuators()));
builder.Connect(constant_zero_torque->get_output_port(),
plant.get_actuation_input_port());
DRAKE_DEMAND(!!plant.get_source_id());
builder.Connect(
plant.get_geometry_poses_output_port(),
scene_graph.get_source_pose_port(plant.get_source_id().value()));
builder.Connect(scene_graph.get_query_output_port(),
plant.get_geometry_query_input_port());
geometry::ConnectDrakeVisualizer(&builder, scene_graph);
std::unique_ptr<systems::Diagram<double>> diagram = builder.Build();
// Create a context for this system.
std::unique_ptr<systems::Context<double>> diagram_context =
diagram->CreateDefaultContext();
diagram->SetDefaultContext(diagram_context.get());
systems::Context<double>& plant_context =
diagram->GetMutableSubsystemContext(plant, diagram_context.get());
Eigen::VectorXd q = plant.GetPositions(plant_context, plant_index);
q[0] = 0.1;
q[1] = 0.5;
q[2] = 0.3;
plant.SetPositions(&plant_context, q);
// Set up simulator.
systems::Simulator<double> simulator(*diagram, std::move(diagram_context));
simulator.set_publish_every_time_step(true);
simulator.set_target_realtime_rate(FLAGS_target_realtime_rate);
simulator.Initialize();
simulator.AdvanceTo(FLAGS_simulation_time);
}
} // namespace kuka
} // namespace examples
} // namespace drake
int main(int argc, char* argv[]) {
gflags::SetUsageMessage(
"bazel run"
"//examples/kuka_iiwa_arm_idc:run_kuka_idc");
gflags::ParseCommandLineFlags(&argc, &argv, true);
drake::examples::kuka::DoMain();
return 0;
}
