Bosch 6000 User's Guide download pdf (Page 172)

Chapter 5. Custom Profiling

157

Arc Segments

90°

180°

270°

Y Axis

Increasing

Degrees

Arcs are more complex to specify than lines, because there are four possible ways to get from

the start point to the end point. The radius of an arc may either be specified directly or implied

by the center specification. In the controller, all path descriptions refer to the X-Y plane. The

general convention describing the X-Y plane, as viewed from a drawing, is as follows. The X

axis is shown as the left-right axis, with left being negative and right being positive. The Y

axis is the up-down axis with down being negative and up being positive. Angles start at zero

and increase in the CCW direction of rotation. A line segment, or the radius of an arc is at

zero degrees if the incremental end-point has a positive X component and zero Y component.

The angle is 90 degrees if the end-point has a positive Y component and zero X component.

Radius Tolerance

Specifications

All arcs have an associated radius. In the controller, the radius may either be specified

explicitly, or implied by a center specification. In both cases, it is possible that the radius

may not be consistent with the specified end-point of the arc. This could be a result of

improper specification, user calculation error, or of round-off error in the internal arithmetic of

the controller. For this reason, the controller allows the specification of a radius tolerance

(PRTOL). The radius tolerance is specified in the same units as the radius and X and Y data.

The radius tolerance has a factory default of ± one step, which is just enough to overcome

round-off errors. The radius tolerance may be specified at any point along the path definition,

and may be changed between one arc and the next. Each arc definition will be compared to the

most recently specified radius tolerance. The radius tolerance should be about the same as the

dimension tolerances of the finished product. The following paragraphs explain how the radius

tolerance is used for the two types of arc specifications, and gives syntax examples for the

radius tolerance specification.

Radius Specified

Arcs

End-

point

Start

Specification of an arc using the radius method requires knowledge of the start point, the end

point, and the sign and magnitude of the radius. The controller knows the start point to be

either the start of the path, or the end of the previous segment. The end point and radius are

provided by the user's program. It is possible to specify an impossible arc by specifying an

end point that is more than twice the radius away from the start point (see drawing at left). In

this case, the controller will automatically extend the radius to reach the end-point, provided

that the automatic radius change does not exceed the user specified radius tolerance. If the

required radius extension exceeds the radius tolerance, the controller will respond with an

execution error, and no arc will be generated.

Example

The following illustration shows the four possible ways to move from the start point to the

end point using an arc of radius 1000. Arc 1 and 2 both travel in the CW direction, arc 3 and

4 both travel in the CCW direction. Arc 1 and 3 are both less than 180 degrees. An arc of

180 degrees or less is specified with a positive radius. Arc 2 and 4 are both greater than 180

degrees. An arc of more than 180 degrees is specified with a negative radius. The example

code below shows the radius tolerance specification and the specifications of arcs 1, 2, 3, and 4

respectively.

SCALE1 ; Enable scaling

PSCLD100 ; Path position scaler

DEF arcs ; Begin definition of path arcs

PRTOL5 ; 5 steps of radius tolerance

PARCP866,500,1000 ; Arc 1, CW < 180 degrees

PARCP866,500,-1000 ; Arc 2, CW > 180 degrees

PARCM866,500,1000 ; Arc 3, CCW < 180 degrees

PARCM866,500,-1000 ; Arc 4, CCW > 180 degrees

END ; End path definition

;***********************************************

;* To compile the arcs path, type "PCOMP arcs" *

;* To run the arcs path, type "PRUN arcs" *

;***********************************************

r =

1000

(0,1000)

Arc 2

r = 1000

Arc 4

End Point

(866,500)

Start Point

(0,0)

Arc 1

Arc 3

1 2 ... 167 168 169 170 171 172 173 174 175 176 177 ... 267 268

Bosch 6000 User's Guide Page 172

Comments to this Manuals

Bosch 6000 User's Guide Page 172

Comments to this Manuals

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