Sweeping Tool Bodies Along a Path

Contents

• 39.1 Introduction
  • 39.1.1 Received and returned arguments
  • 39.1.2 Options available when sweeping tool bodies
• 39.2 Specifying a tool body
• 39.3 Specifying a path
• 39.4 Sweeping along 3D paths
• 39.5 Positioning the tool on or off the path
• 39.6 Specifying that path edges lie on a spun surface
• 39.7 Simplifying faces of a swept tool body
• 39.8 Specifying corner types
• 39.9 Performing boolean operations with solid tool bodies

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39.1 Introduction

With this functionality:

• PK_BODY_make_swept_tool takes a tool body, spins it about an axis, and then sweeps the resulting spun body along a path to create a swept body.
• The resultant body is described by the envelope of the tool body as it is swept along the path.

You can use this function to construct bodies that represent regions to be cut from a solid body using a machine tool. For example, you can create a region to be cut out using PK_BODY_make_swept_tool and then subtract this region from the solid body either using a boolean operation, as shown in Figure 39-1, or the sweep_boolean option as described in Section 39.9, “Performing boolean operations with solid tool bodies”.

Figure 39-1 Creating swept bodies for use in cutting out regions from a body

For examples of this functionality, see the code examples in the C++\Code Examples\Modelling\Profiling folder in your Parasolid installation folder.

39.1.1 Received and returned arguments

PK_BODY_make_swept_tool receives and returns the following arguments:

tool

tool_axis

path

options

tracking

swept_tool

39.1.2 Options available when sweeping tool bodies

PK_BODY_make_swept_tool contains an options structure that provides the following options:

tolerance

allow_rationals

want_edge_tracking

have_lock_direction

lock_direction

tool_site

n_cap_faces

cap_faces

place_tool_on_path

sweep_boolean

target

corner_type

have_turn_axis

turn_axis

turn_edges

update

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39.2 Specifying a tool body

The tool supplied to PK_BODY_make_swept_tool has the following restrictions:

• It must be a solid body.
• It must be convex.
• It must not be disjoint.
• It must intersect the axis as defined by the tool_axis . This is so that when the tool body is spun about the axis , the resulting cross-section forms a single connected set of curves for use as a profile during the sweep operation. (In other words, the profile body has no holes.)

It does not matter where the tool is located with respect to the path . By default, PK_BODY_make_swept_tool positions the tool so that the location of the tool_axis is on the specified path before sweeping. If you do not want to move the tool onto the path , you can set place_tool_on_path to PK_LOGICAL_false. See Section 39.5, “Positioning the tool on or off the path”, for more information.

The tool_axis defines the axis about which the tool body is spun. The tool does not need to be rotationally symmetric about the tool_axis . The shape of the resultant body can vary depending on the position of the tool_axis as illustrated in Figure 39-2.

Figure 39-2 The effect that changing the location of the tool axis has on the result body

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39.3 Specifying a path

The path supplied to PK_BODY_make_swept_tool:

• must be planar and lie in a plane orthogonal to the tool_axis, unless a lock_direction controlling the orientation of the tool is supplied.
• may be closed (in which case the resulting swept body is called a closed sweep). It may also self-intersect: self-intersections in the resulting swept body are healed automatically.
• need not be G1 continuous, so long as a vertex is placed at each G1 discontinuity. The shape of the swept body at any G1-discontinuous vertex is formed by spinning the tool body on its axis centred at the G1-discontinuous vertex. Figure 39-3 shows a top-down view of a simple example that illustrates this.

Figure 39-3 Forming swept bodies at G1-discontinuities on the path

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39.4 Sweeping along 3D paths

For non-planar paths or when the tool spin axis is not orthogonal to the path, you must supply a lock_direction to specify the orientation of the swept tool. It must be a unit vector and is used if have_lock_direction is PK_LOGICAL_true. Figure 39-4 shows a cylindrical tool with a set lock_direction being swept along a 3D path.

Figure 39-4 Sweeping along a 3D path

The lock_direction does not have to be in the same direction as the tool_axis and their relative directions can affect the overall shape of the result. Figure 39-5 (a) shows the result when the direction of the lock_direction and tool_axis are the same, and (b) shows the result when the direction of the lock_direction is different to that of the tool_axis .

Figure 39-5 Difference in the shape of the result body when the direction of lock_direction is the same (a) and different (b) to the direction of tool_axis

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39.5 Positioning the tool on or off the path

Using the place_tool_on_path option, you can choose whether or not to place the tool on the path before sweeping. When set to PK_LOGICAL_false, the tool will not be moved onto the path and will be swept from its initial position if the following conditions are met:

• the tool_site specifies a positioning vertex for the path which indicates the location of tool_axis and enables the body to be placed on the path for sweeping.
• the tool_axis intersects the plane perpendicular to the sweep direction at the tool_site taking any lock_direction specified into account.
• the path is G1 continuous.

By default, the tool will be moved onto the path before it is swept. The results of both values are illustrated in Figure 39-6 and Figure 39-7.

Figure 39-6 Sweeping a tool that lies on the path

Figure 39-7 Sweeping a tool that lies off the path

Any vertex on the path can be used as a positioning vertex. Figure 39-8 and Figure 39-9 show how the location of the positioning vertex on the path can affect the overall shape of the resultant swept profile.

Figure 39-8 Sweeping along a path using a vertex at the start of the path as a positioning vertex

Figure 39-9 Sweeping along a path using a vertex in the middle of the path as a positioning vertex

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39.6 Specifying that path edges lie on a spun surface

You can use the have_turn_axis, turn_axis , and turn_edges options to specify a subset of the path that is considered to turn around the turn_axis . Specifying these options can improve the quality of the resulting swept body, for example when simulating lathing and turning operations.

If have_turn_axis is PK_LOGICAL_true:

• the edges of the path specified in turn_edges are treated as lying on a body spun around the supplied turn_axis . The tool motion of the sweep corresponding to these edges will be determined using the turn_axis together with the radial directions from turn_axis .
• the turn_axis must lie in the same direction as the lock_direction .

Figure 39-10 Specifying the turn_edges in the sweep operation

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39.7 Simplifying faces of a swept tool body

If there are faces on the tool body whose precise geometry is not significant for downstream operations, they can be supplied as cap_faces to enable Parasolid to generate simpler geometry for these faces. These cap faces are often used to close off the tool volume or to represent the shaft of the tool.

Figure 39-11 (a) shows a tool body sweep without cap_faces supplied. Figure 39-11 (b) shows the same tool body sweep where the faces coloured red in the tool have been supplied as cap_faces . Parasolid geometrically simplifies these cap_faces to a spherical face that is smoothly joined to the tool and the sweep operation proceeds with this remodelled tool.

Swept faces generated from cap_faces are returned in a Parasolid Report of type PK_REPORT_record_type_3_c with a status of PK_REPORT_3_sweep_tool_cap_c. This contains a PK_sweep_tool_cap_t status to indicate whether the swept tool volume is either enclosed (PK_swept_tool_cap_enclose_c) or undercut (PK_sweep_tool_cap_undercut_c) by the simplified cap geometry.

See Chapter 11, “Using Reports”, for more information about the Parasolid report mechanism.

Figure 39-11 Sweeping a tool body with and without supplying cap_faces

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39.8 Specifying corner types

When the sweep path is not G1-continuous, you can choose to produce either a rounded or mitred corner at each sharp corner on the path using the corner_type option. By default, rounded corners are produced. When set to PK_sweep_corner_type_mitre_c, each section of the sweep is linearly extended to produce mitred corners.

Figure 39-12 Producing rounded or mitred corners when sweeping with a tool body

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39.9 Performing boolean operations with solid tool bodies

As discussed in Section 39.1, you can use PK_BODY_make_swept_tool to construct bodies that represent regions to be cut from a solid body and then use Parasolid’s boolean operation to subtract the specified region from the solid body. See Chapter 52, “Manifold Booleans” for more information on boolean functionality.

Alternatively, you can perform both the sweep and boolean operation in one function call, using the sweep_boolean option in PK_BODY_make_swept_tool. When simulating lathing operations for example, the volume of interest is often the volume remaining after removal of material from the target body. In these circumstances, setting the sweep_boolean option allows the complexity of the modelling operations to be reduced.

To use this functionality you must specify an appropriate target body in addition to the chosen boolean operation (either subtract or intersect) using the sweep_boolean option. This takes the following values:

Figure 39-13 shows an example of this functionality. When sweep_boolean is set to PK_sweep_boolean_subtract_c the swept tool volume is subtracted from the specified target body to create a result body. When set to PK_sweep_boolean_intersect_c the specified target volume is intersected with the swept tool to create a result body

With this option, the boolean operation occurs immediately after the swept tool has been swept along its path and the swept tool returned is the target body which is the result of the boolean operation between the sweep and boolean combination.

Figure 39-13 Performing boolean operations with a swept tool body

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