About Geometric Servo Motors
If you select points or planes as references when defining a servo motor, you are creating a geometric servo motor. Geometric servo motors are used to create complex 3D motions such as a helix.
When you select Geometry on the Type tab of the Servo Motor Definition dialog box, you must select a point or plane as a reference as well as a motion direction.
You can create the following types of geometric servo motors:
• A plane-plane rotation servo motor moves a plane in one rigid body at an angle to a plane in another rigid body. During a motion run, the driven plane rotates about a reference direction, with the zero position defined when the driven and reference planes are coincident.
Because the axis of rotation on the driven rigid body remains unspecified, a plane–plane rotation servo motor is less restrictive than a servo motor on a pin motion or cylinder motion. Thus, the axis of rotation in the driven rigid body may change as a function of time.
A plane-plane rotation servo motors can be used to define rotations around a ball joint. Another application of a plane-plane rotation servo motor would be to define a rotation between the last rigid body of an open-loop mechanism and Ground, such as a front loader.
• A plane-plane translation servo motor moves a plane in one rigid body with respect to a plane on another rigid body, keeping one plane parallel to the other. The shortest distance between the two planes measures the position value of the servo motor. The zero position occurs when the driven and reference planes are coincident.
In addition to the prescribed motion, the driven plane is free to rotate or translate in the reference plane. Thus, a plane-plane servo motor is less restrictive than a servo motor on a slider or a cylinder joint. If you want to explicitly tie down the remaining degrees of freedom, specify additional constraints such as a connection or another geometric servo motor.
A plane-plane translation servo motor can be used to define the translation between the last link of an open-loop mechanism and Ground.
• A plane-point translation servo motor is the same as a point–plane translation servo motor, except that you define the direction in which a plane will move relative to a point. During a motion run, the driven plane moves in the specified motion direction, while staying perpendicular to it. The shortest distance from the point to the plane measures the position value of the servo motor. At a zero position, the point lies on the plane.
You cannot define the orientation of one body with respect to the other using only a plane-point servo motor. The driven plane is free to move perpendicularly to the specified direction. Lock these degrees of freedom using another servo motor or connection. By defining x, y, and z components of motion on a point with respect to a plane, you can make a point follow a complex 3D curve.
• A point-plane translation servo motor moves a point in one rigid body along the normal of a plane in another rigid body. The shortest distance from the point to the plane measures the position value of the servo motor.
You cannot define the orientation of one rigid body with respect to the other using only a point-plane servo motor. The driven point is free to move parallel to the reference plane, and may thus move in a direction unspecified by the servo motor. Lock these degrees of freedom using another servo motor or connection. By defining x, y, and z components of motion on a point with respect to a plane, you can make a point follow a complex 3D curve.
• A point-point translation servo motor moves a point in one rigid body in a direction specified in another rigid body. The shortest distance measures the position of a driven point to a plane that contains the reference point and is perpendicular to the motion direction. The zero position of a point-point servo motor occurs when both the reference and driven point lie in a plane whose normal is the motion direction.
The point-point translation servo motor is a very loose constraint that must be used carefully to get a predictable motion. You cannot define the orientation of one rigid body with respect to the other using only one point–point servo motor. In reality, you would need six point-point servo motors for this.
The driven point is free to move perpendicularly to the specified direction, and may do so if you do not specify otherwise. Lock these degrees of freedom using another servo motor or connection. By defining x, y, and z components of motion on a point with respect to a plane, you can make a point follow a complex 3D curve.