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70 lines
2.9 KiB
70 lines
2.9 KiB
2 years ago
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Simple Gripper Simulation
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=========================
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This simple gripper demo is used to exercise MultibodyPlant's contact modeling
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in a gripping scenario. SceneGraph is used for both visualization and contact
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handling.
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This example models a gripper with two fingers. The right finger is fixed to the
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main body of the gripper, while the left finger has a prismatic joint to allow
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opening and closing the grip. The grip force can be specified with the command
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line option `--gripper_force`, which defaults to 10 Newtons of force. If we
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provide a value of exactly zero, the fingers of the gripper will be set to be at
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`--grip_width` distance (in meters) from each other. When `--gripper_force > 0`,
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`--grip_width` specifies the initial condition for the fingers position.
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The demo also permits specifying a vertical harmonic motion of the gripper to
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evaluate the performance of the grip when the gripper is undergoing forced
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motions. The parameters controlling this motion are `--amplitude`, to specify
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the amplitude of the oscillations in meters and, `--frequency` to specify the
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frequency of the oscillations in Hertz. Additionally, the user might like to
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change the direction of the forced oscillations to either be in the horizontal
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or vertical direction. This can be accomplished by changing the `<axis>`
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specified for the `<joint>` named "translate_joint" in the SDF for the gripper
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model, `simple_gripper.sdf`. Only vertical or horizontal forced motions are
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supported in this example and thus the axis must either be the x-axis or the
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z-axis. Otherwise an exception is thrown communicating this fact. There is no
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gravity for the forced vertical oscillations case.
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Fixed Gripper with Gravity
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--------------------------
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To run a case with gravity but no forced oscillations, set the `<joint>` axis
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for the joint named "translate_joint" to be the x-axis in the SDF file.
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The parameter `--gripper_force` specifies the grip force while `--grip_width`
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specifies the initial condition for the position of the fingers.
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If the gripper force is set to zero, the fingers will be placed at a fixed
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`--grip_width` distance apart. The latter is an important test case since it
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eliminates the additional complexity introduced by having moving fingers.
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Prerequisites
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-------------
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From your `drake` workspace directory you first need to build this example and
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the visualizer.
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Open a visualizer window
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```
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bazel run //tools:meldis -- --open-window &
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```
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Build this example with
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```
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bazel build //examples/simple_gripper
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```
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Running the Example
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-------------------
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Launch the simulation with
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```
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./bazel-bin/examples/simple_gripper/simple_gripper --simulation_time=10.0 \
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--simulator_target_realtime_rate=1.0
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```
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where for this particular invocation example we are specifying the simulation
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time in seconds as a command line option. To get a list of command line options
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for this example run
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```
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./bazel-bin/examples/simple_gripper/simple_gripper --help
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```
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which will also provide a description for each option.
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