3 Getting Started

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3 Getting Started

• 3.1 The main window and controls
• The Camera mode
• The Interaction mode
• 3.2 Grasp example
• 3.3 Dynamics example
• 3.4 The menus

To get started, use the File -> Open menu, and load the simulation world file dlr_flask.wld. Note that by default GraspIt! will look for world files in $GRASPIT/worlds. This is a very simple simulation world containing nothing except a hand (the DLR model) and an object (a flask).

In general, you can also start with an empty simulation world and populate it by importing robots and objects, one at a time, using the Import options in the File menu. You can then save a simulation world into a world file, like the one that we just opened. In this quick tutorial, we will be using a couple of simulation worlds supplied with the distribution.

3.1 The main window and controls

The most part of the GraspIt! main window is occupied by the Inventor viewer, which renders the virtual world. On the right side there is a vertical toolbar: this is the Inventor toolbar which is responsible for camera interaction.

The first two buttons on the Inventor toolbar determine which state the viewer is in. When is selected, the viewer is in Interaction mode. This is the only mode in which you can interact with the objects in the simulation world. When is selected, the viewer is in Camera mode. This is the only mode in which you can move the camera.

You can also toggle between Interaction mode and Camera mode by pressing the <ESC> or <ALT> keys, although this seems not to work on all systems.

The Camera mode

When the viewer is in Camera mode, you can move the virtual camera in the following ways:

• Rotate - Hold down the left mouse button and drag;
• Translate - Hold down <CTRL> and the left mouse button and drag; alternatively, hold down the middle mouse button and drag;
• Zoom - Hold both the left and middle mouse buttons and drag, or rotate the wheel on a wheel mouse.

In addition, the following buttons on the Inventor toolbar are useful:

• - This automatically moves the camera so that the entire scene fits in the viewer window;
• - The seek tool allows you to click on an object in the scene. After you click, the camera zooms in on the object, which also becomes the center of rotation.

Take a moment to move the camera around and familiarize yourself with its controls.

The Interaction mode

When the viewer is in Interaction mode, you can interact with the objects in the scene. The type of interaction is determined by the following button in the GraspIt! toolbar: :

• - Translate or set joints. Clicking on a body or the base (palm) of a robot causes a box to be drawn around it. This box acts as a translation manipulator. By clicking on the sides of the box and dragging the mouse, the body or robot can be translated in 2 dimensions that are aligned with the face of the box that was clicked. Holding down <SHIFT> constrains this motion to one axis. If a robot is selected and moved.

  Clicking on a kinematic chain causes joint draggers to be drawn for each DOF on that chain. You can then use these draggers to move the joints of the robot.

• - Rotate. Clicking a body or robot base link brings up a spherical rotation manipulator. Dragging the ball allows rotation of the selected item in three dimensions. By clicking one of the stripes, the body can be rotated about one axis at a time. By dragging the cross hairs, the ball can be re-centered to rotate about a different point. The limitations concerning connected robots applies to rotation as well.
• - Select. Clicking a body will select it, and this is indicated with a wireframe overlay. Holding down <SHIFT> allows multiple bodies to be selected, or clicking on an already selected link of a robot will select the whole robot. Once a body (or bodies) has been selected, its collision and material properties are shown in the next part of the toolbar. They can then be changed or additional properties can be changed using the menu item described below. After a body is selected, the user may remove the body from the world by pressing <DEL>.

Try to use the tool to flex the fingers of the robot. Note that once a finger touches the object, a contact is marked and no more flexion is allowed. The same behavior applies for moving objects or robots around.

The following buttons in the GraspIt! toolbar apply to the currently selected body (if any):

• - Toggle Collisions. There are 3 different ways to use this property:
  • if no body is selected, this button allows collision checking for the entire world to be switched on or off.
  • if one or more than two bodies are selected, this button sets the collision checking for those bodies. A body that has collision checking turned off can pass through ANY other body.
  • if two bodies are selected, this button allows collision checking between ONLY that pair of bodies to be disabled.
• - Material. This sets the material for the selected bodies, which affects the coefficient of friction when contacts arise.

Try to disable collisions for the entire simulation world. Note that now you can move objects or flex fingers freely, even if that results in a collisions. Make sure you move all objects out of collisions before you re-enable collision checking; otherwise, you will not be able to move them around.

You can also create one or more contacts between the hand and the object. Once you have a contact, select one of the bodies in contact (such as the robot link that is touching the flask, or the flask itself) and change its material. Notice how the friction cone that marks the contact changes as well.

3.2 Grasp example

Start by loading the simulation world dlr_flask.wld again, to make sure all the world elements are in their original positions. The use the menu Grasp -> Auto Grasp. This will cause all the fingers of the robot to flex (more details can be found in the robot configuration file) until contact with the flask prevents all further motion. You now have a grasp.

Use the Grasp -> Quality Measures... menu to create a new quality measure that will be used on this grasp. By default, the quality measure dialog that appears will create a new quality measure called New Quality Measure of the Epsilon type using an L1 Grasp Wrench Space. Click Add/Edit, and then click OK. The new quality measure, along with its value, will be displayed in the lower left part of the GraspIt! main window.

You can also create a projection of the Grasp Wrench Space for this grasp. Use the Grasp -> Create GWS Projection menu. Then click the three checkboxes marked tx, ty and tz and click OK. GraspIt! will display the space of forces that this grasp can apply without a net torque. Note that if you change the camera in the main GraspIt! viewer, the camera that shows the GWS projection moves as well. The axes of the GWS projection are always aligned with the axes of the main viewer.

3.3 Dynamics example

Start by loading the simulation world barrettGlassDyn.wld. Then, start the dynamics engine by pressing the button on the Dynamics toolbar. Note that the robot joints move slightly and the glass slowly rolls on the table. The PD controllers in the robot joints are simply maintaining the current position against gravity.

Use the Grasp -> Auto Grasp menu to close the fingers of the hand. Note that the hand starts closing, then lifts the glass into its grasp. After the grasp stabilizes, select the glass and change its material properties to frictionless. The glass then slips out of the grasp and ends up rolling off the table. You can pause the dynamics engine at any time by clicking the pause button in the dynamics toolbar.

3.4 The menus

Here is a subset of the functionality in the menus (I hope to update this section soon):

• File Menu
  • New Empties the current world and resets the simulation time.
  • Open... Loads a new world configuration.
  • Save, Save As... Saves the current world configuration. Velocities are not saved.
  • Save Image... Renders the scene using the current camera and saves the image in jpg format. The image will be antialiased.
  • Import Robot... Loads a robot from a robot configuration file and places it at the world origin. After importing a robot or body, click view all if the imported object does not fit in the viewer.
  • Import Object... Loads an Inventor model and places it in the world as a graspable body. The Inventor file must have mass and material defined in the comments. The body is made transparent so that contacts can be seen.
  • Import Obstacle... Loads an Inventor model and places it as a static object in the world. These objects may be moved by the user but their motions are not computed during dynamic simulation.
  • Edit Settings... Allows the user to change persistant program settings. The settings are stored in the registry in Windows, and in an rc file in Linux. See below for a description of this dialog box.
  • Exit Exits the program.
• Element
  • Translate Same as translate toolbar button. See above.
  • Rotate Same as rotate toolbar button. See above.
  • Select Same as select toolbar button. See above.
  • Collisions ON/OFF Same as collision toggle toolbar button. See above.
  • Body Properties... Brings up a dialog box that allows the user to edit the properties of the currently selected bodies. See below for a description of this dialog box.
• Grasp
  • Auto Grasp Starts an auto-grasp. When the dynamics are not running, this closes the fingers of a hand until joint limits are reached or contacts prevent further motion. The relative velocity of the joints is defined in the robot configuration file. When dynamics are running, a trajectory generator will create a position trajectory that will close the fingers. The joint controllers will then use these positions as set points and adjust the joint forces.
  • Create GWS Projection... Opens a dialog box to allow the user to choose a projection of the 6D grasp wrench space. After the projection is chosen, GraspIt! opens a new window showing the projected wrench space. The volume is updated each time the grasp changes.
  • Quality Measures... Allows the user to create a new quality measure that will be evaluated each time the grasp changes. (More documentation on this soon.)
  • Planner... Opens a dialog box containing settings for the automatic grasp planner. At this time this only works with the Barrett hand.

3 Getting Started

Contents