《机械原理》课件第4章平面机构的力分析(.ppt

1、JM 返回返回v1221 Q0.150.1 0.120.10.05 0.10.2 0.3 0.16 0.180.05 0.150.1 0.150.15 0.180.070.15 0.160.150.07 0.120.280.160.15 0.210.07 0.150.15 0.200.04 0.10.3 0.50.12 0.150.80.5摩摩 擦擦 系系 数数摩擦副材料摩擦副材料静静 摩摩 擦擦动动 摩摩 擦擦无润滑剂无润滑剂有润滑剂有润滑剂无润滑剂无润滑剂有润滑剂有润滑剂钢钢钢钢钢铸铁钢铸铁钢青铜钢青铜铸铁铸铁铸铁铸铁铸铁青铜铸铁青铜青铜青铜青铜青铜皮革铸铁或钢皮革铸铁或钢橡皮铸铁橡皮铸铁

2、PN21F21JM 返回返回：Q12N”21N21Q12F21=f N21+f N”21N21 N21=N”21=Q/(2sin)N21=N21 k=1/2 F21=f N21 F21=f N21QN21N21=QF21=f N21=f QF21=-=-QN21+N”21=-QN”21N21QN21=|N21|12N21=(f/sin)Q=fv Q=f k Q=fv Q=fv Qfv=kQkQ|N21|JM 返回返回QPv1221 R21=N21+F21R21N21F21tg=F21/N21，:R21V V1212 (90(90+)=fN21/N21=fJM 返回返回;：P+R+Q=0P+R+

3、Q=0：？：？：12QRNF21nnvPRPQ P=Qtg(P=Qtg(+)12QNF21nnvPRQPR-+：P+R+Q=0P+R+Q=0 PP=Qtg(=Qtg(-)：？：JM 返回返回1530330JM 返回返回d1d3d2Qd2lQP：tgvv=l/d2=zp/d2 )(QtgPJM 返回返回)(2222QtgddPM)(QtgP)(2222QtgddPMPMfd2JM 返回返回NcosQN:fv=f /cosNNNNQQ Q)(22vQtgdM)(22vQtgdMNcosQ，NQ v arctgarctg fv：NN/cosJM 返回返回 F21N21F21R2112MdQMf R2

4、1-Q,Md=Mf =Q21r=k f Q=fv Q Mf=F21 r=fv rQ=R21JM 返回返回N21 F21R2112Md QMf21r21rMdMf21QN21F21R21 F21 R21-Q,Md=Mf =Q=kf Q=fv Q Mf=F21 r=fv rQ=f N21 rJM 返回返回1、由力平衡条件，初步确定总反力方向（受拉或受压）、由力平衡条件，初步确定总反力方向（受拉或受压）2、对于转动副有：、对于转动副有：R21恒切于摩擦圆恒切于摩擦圆3、对于转动副有：、对于转动副有：Mf 的方向与的方向与1212相反相反14MrP2123R12R32R439090+R23R21R41

5、v34PMr对于移动副有：对于移动副有：R21V V1212(90(90+)2 13ABC4JM 返回返回 ABCD1234Md142123Q R R12R R32R R21MdR R41R R23R R4314Q4343R R43R R43+R R23+Q=0R R23=Q(cb/ab)QbaR R23c：？：MdQ(cb/ab)Q(cb/ab)llR R21=-R-R23 JM 返回返回d dsds2d2d dF=fdNdMf =dFdN=pdsdN=pds,fpdsMRrfRrfdpfM22)(/22rRQpRrfdfpM2RrpdsQ Mf =f Q(R+r)/2,=f dN=fpds

6、=fpds)(3233rRfp2233)(32rRrRfQRrdpf22)(22rRfp)(2rRp212r2RrRMQMfJM 返回返回 W、Mdv123456FrR（不计摩擦）（不计摩擦）RnnCOR（JM 返回返回2PL+PhJM 返回返回D1Q2举例：举例：ABCEF23456S2Q5PrW1S5xxGJM 返回返回ABCDEF123456Q2S2Q5PrW1S5xxG P(a,d)bcefbn2cn3en4fP(a,d)JM 返回返回ABCDEF123456Q2S2Q5PrW1S5xxGP(a,d)bcefbn2cn3en4fP(a,d)PI2=m2 aS2=(Q2/g)uaps2M

7、I2=JS22=JS2 atCB/l2=JS2 ua n2c/l2hPI2PI5=m5 aS5=(Q5/g)uapfPI5S2JM 返回返回ABCDEF123456Q2S2Q5PrW1S5xxGhPI2PI5234516JM 返回返回ABCDEF123456Q2S2Q5PrW1S5xxGhPI2PI545R34R54Q5PI5PrR45R65R34=R54=R45RI5Q5PrR65R45=0+Q5PrPI5R65R45abcdeR65=uf deR45=uf ea可得：可得：JM 返回返回1GAB6W1xxR43 Q5PrPI5R65R45CE23Q2S2hPI2DR12nR12tR63nR

8、63tR63tQ2PI2R12nR63n=0+R12t+R43R12,R63,R23PI2abcdefQ2gh-R63tkR12R63R23R43R63=0+R23R43JM 返回返回1GAB6W1xx 研究原动件的力平衡：研究原动件的力平衡：Q5PrPI5R65R45R21R63nPb,R61 PI2abcdefQ2gh-R63tkR12R63PbR21R61=0+R23R43PbR61R61PbJM 返回返回 WdWrWf=EE00,m m t (t)=(t+T(t)=(t+Tp p)WG=0,E=0E=0 JM 返回返回 N Nr r/N/Nd d0 0N Nr r/N/Nd d =Q

9、Q vQ Q /P/P0 0vp pP P0 0 vp p /P/Pvp pP P0 0/P/PM Md0d0 /M Md dm m t 停止停止 WdWrWfWG=EE00Wd=Wr+WfPvp pvQ QQ机械机械=Q Q vQ Q /P/P vp p1 1P0 JM 返回返回实际驱动力理想驱动力：)(22vQtgdM 理想工作阻力实际工作阻力实际驱动力矩理想驱动力矩理想工作阻力矩实际工作阻力矩Pvp pvQ QQ Q0JM 返回返回 9 单头蜗杆单头蜗杆 0.700.75JM 返回返回 JM 返回返回dkNNkidNN1NdNkkirNN1drNN123121 kkdNNNNNNNNk

10、21kNNN 21kkkNNNNNN 212211N1N2Nk-112k21kNNN kkNNN 2211N1N2NkN1N2Nk12kNdNrminmin Q0 Q0 JM 返回返回00tg(-v v )0 0，P132R32R13QR12Q=R23 cos(-2)/cos-2)/cosQR13R23PR12R3290+9090-+2-+2-9090-(-)-(-)-29090-tg(-v v )/tg()v vv32R23R R13+R R23+Q=0大小：大小：？方向：方向：R R32+R R12+P=0大小：大小：？方向：方向：P=R32 sin(-2)/cos-2)/cos P=Q tg(-2)-2)tg(-2)-2)0022v v=8.7=8.7f =0.15=0.15JM 返回返回