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This paper used Pro/E’s datum-graph function, to create the follower’s displacement line graph, and to call the displacement line graph program according to the setting of motion laws, and then to control cam section’s shape through the displacement line graph which was used at variable section sweep in modeling. Thereby it was realized that the wholly parametric design for cam profile which could automatically change with motion law’s difference. And based on this, cam-follower pair was generated. Furthermore, by using the technology of virtual assembly and motion simulation, the visible assembly interference detection and rationality analysis about product design can be realized in design phase, which will lay the foundation for the follow-up virtual manufacturing.
Fig.1.Cam mechanism motion process Fig. 2. Graph3
2. Displacement-angle relations of follower
Given cam rise travel angle is δt, return travel angle is δh, follower's lift is h, the cam angle is δ, The velocity of the follower in rise travel is:
• Constant velocity: S=hδ/δt
• constant acceleration and constant deceleration:
S1=2hδ2/δ2 (in the half travel of constant acceleration);S2=h-2h(δt-δ)2/δ2 (in the half travel of constant deceleration);
• cosine acceleration:
• sine acceleration:
The velocity of the follower in return travel is:
• Constant velocity:
• constant acceleration and constant deceleration:
(in the half travel of constant acceleration);
(in the half travel of constant deceleration);
• cosine acceleration:
• sine acceleration:
3. The steps to build model
3.1. Build the relevant parameter
By using the parameters function which Pro/E provides, parameters, liked base circle radius, deviation distance, roller radius, rise-travel law, return-travel law, and so on, were set up as showed in table 1.
Table 1. The parametric table
3.2. Create the displacement line graph of follower
To execute the order of Insert-Model Datum-Graph, input sequentially graph name as ‘Graph1’-‘Graph4’, the displacement line graphs were designed separately which were corresponding to cam rise-travel angle of the four kinds of motion laws as constant velocity, constant acceleration and constant deceleration, cosine acceleration and sine acceleration. In the same way, ‘Graph5’ and ‘Graph10’ were designed corresponding to far stop and nearly stop travel angle, and ‘Graph6’-‘Graph9’corresponding to return travel, as showed in Figure 2.
In order to make each displacement line graph is corresponding to its motion law, it is necessary to input separately the displacement-angle relations of Datum-Graph:
/* Graph1 (the displacement and angle of constant velocity in rise travel)
sd3=dtat
sd4=h
/* Graph2(the displacement and angle of constant acceleration and constant deceleration in rise travel)
sd30=dtat/6
sd29=(2*h/(dtat^2))*(sd30)^2
sd26=2*dtat/6
sd25=(2*h/(dtat^2))*(sd26)^2
sd23=3*dtat/6
sd22=(2*h/(dtat^2))*(sd23)^2
sd20=4*dtat/6
sd19= h-(2*h/(dtat^2))*( dtat-sd20)^2
sd17=5*dtat/6
sd16= h-(2*h/(dtat^2))*( dtat-sd17)^2
sd10=dtat
sd12= h
/* Graph3(the displacement and angle of cosine acceleration in rise travel)