Design Data Output

Here are typical design data produced by the software model. The data are generated by moving the platform with a fixed angular orientation over the area of the machine bed, recording values at points on a regular grid. In this case the platform is unrotated and horizontal. The coordinate axis system used in the model has its origin at the centre of the machine base. The z axis is vertical, and the x and y axes are parallel to the sides of the machine bed. The data are displayed as an array of planes at a regular z spacing covering the range of interest. For the nomenclature used in the software model see these diagrams:

	diagram 1	Nomenclature for the mechanism.
	diagram 2	Nomenclature for the leg pair triangles and the platform.

Parameters

These are the static parameters for a machine version define by defineParameters.C. Dynamic parameters determining the platform position and orientation are defined in the different program main functions.

parameters

Range Checks

The grid shows locations which the mechanism can reach as dots. L (Long) indicates that the range is restricted by the maximum leg length. S (Short) indicates that the range is restricted by the minimum leg length.

range checks

Resolution Errors

The discrete resolution of the mechanism actuators introduces a varying platform position error. The effect is estimated in the model by simple rounding. To get closer to the real situation it would be necessary to model the control system. The data are shown as a multiple of the resolution, rounded up. In this case the maximum error is less than twice the resolution. Other cases with the platform rotated show up to five times the resolution, though it is rarely this high.

resolution errors

Angles

These data are needed for joint design, and it is necessary to consider a number of platform orientations to get the full picture. Refer to the diagrams for the nomenclature. Angles are given in degrees.

	min angle ACB	Leg pair triangle bottom angle.
	min angle ACF	Angle of leg to bottom joint long axis.
	min angle BAC	Leg pair triangle top angle.
	min angle GCH	Angle of leg pair triangle plane to platform plane.
	min angle GCV	Angle of leg pair triangle plane to horizontal.

	max angle ACB	Leg pair triangle bottom angle.
	max angle ACF	Angle of leg to bottom joint long axis.
	max angle BAC	Leg pair triangle top angle.
	max angle GCH	Angle of leg pair triangle plane to bottom plane.
	max angle GCV	Angle of leg pair triangle plane to horizontal.

Forces and Displacements

The mechanism stiffness is of great importance in precision applications such as machine tools. The stiffness can be tailored to the duty by choosing appropriate sizes for the main leg components. The model shows that the mechanism is sensitive to backlash, and that preloaded joints are desirable. Cutter force magnitude, direction and position in the model is defined in generateDesignData.C. The data given here result from a nominal cutter force with components of 50N (5KgF) in each of the x and y directions. Forces are given in Newtons, displacements in microns (micrometres).

	min leg force
	max leg force
	cutter displacement

LME Hexapod Machine

Laboratory For Micro Enterprise