GB2073843A - Mid-Point Dwell Linkage System - Google Patents

Abstract

A mid-point dwell linkage system has a cycloidal drive which provides mid-stroke slowdown for presses and lifting devices, particularly simpler forms of bottom drive hydraulic presses, knee drives and automation mechanisms. The system comprises a fixed sun gear (16), a crank (18) rockable on the sun gear axis and carrying a planet gear (21) meshing with the sun gear, an eccentric (27) fixed to the planet gear shaft (19) and a lift arm (23) on the eccentric and connectable (at 46) to a member to be driven. <IMAGE>

Description

SPECIFICATION Mid-Point Dwell Linkage System The invention relates to cycloidal drives which have reduced travel speed at mid-stroke to minimize shock and reduce noise level for reciprocating parts, for example when workpieces are being lifted or conveyed.

It is an object of the present invention to provide a novel and improved mid-point dwell linkage system of the cycloidal type which may be used in simpler forms of bottom drive hydraulic presses as well as lifter mechanisms of stool type C frame knees and cylinder operated automated parts conveyors.

According to the invention there is provided a mid-point dwell linkage system comprising a fixed gear, a drive shaft rockable on the axis of said fixed gear, a crank arm fixed to said shaft, an eccentric gear rotatably mounted at the outer end of said crank and meshing with said fixed gear, an eccentric secured to and rotatable on the axis of said eccentric gear, and a lift arm having an inner end rotatably mounted on said eccentric and an outer end having means for connection to a driven member.

A preferred aspect of the invention provides a midpoint dwell linkage system comprising a pair of pillow blocks, a rockable shaft supported by and extending between said pillow blocks, a drive coupling on said shaft, a fixed sun gear concentric with said shaft inside one of said pillow blocks, a pair of spaced parallel crank arms secured to said shaft between said fixed gear and the other pillow block, an eccentric gear shaft rotatably mounted at the outer ends of said crank arms, an eccentric gear of substantially smaller diameter than said sun gear secured to said eccentric gear shaft and meshing with said sun gear, an eccentric fixed to said eccentric gear shaft between said crank arms, a lift arm having an inner end rotatably mounted on said eccentric, said lift arm being of curved construction between said inner and outer ends, whereby said lift arm will clear said drive shaft during movement between extreme positions, and a driven member secured to the outer end of said lift arm.

The invention will be further described by way of example, with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a linkage system embodying the invention; Figure 2 is a schematic view showing the position of the parts when the lift arm is in its lowermost position; Figures 3 to 8 are views similar to Figure 2 showing the movement of the parts when carrying the lift arm to its uppermost position, as well as the locus of movement of the eccentric axis; Figure 9 is a chart showing the variation of lift stroke with time with a constant speed of the drive shaft; Figure 10 is a perspective view showing the application of the linkage system to the bottom drive of a hydraulic press;; Figure 11 is a perspective view showing the linkage system appied as the lifting device of a stool type C frame knee, and Figure 12 is a perspective view showing the linkage system as applied to the lifter mechanism of an automated parts conveyor.

The linkage system 11 as shown in Figure 1 comprises a pair of pillow blocks 12 and 1 3 in spaced relation. A shaft 1 4 extends between and is supported by these pillow blocks and carries a coupling 1 5 outside pillow block 13 for connection to a source of power.

A fixed gear 1 6 in the form of a sun gear is secured immediately inwardly of pillow block 12 and is concentric with shaft 14. A pair of crank arms 1 7 and 18 are secured in spaced parallel relation to shaft 14 between sun gear 1 6 and pillow block 13. An eccentric gear shaft 1 9 is rotatably mounted at the outer end of crank arms 17 and 1 8. This shaft extends between the crank arms and outwardly toward pillow block 12.

An eccentric gear 21 is secured to the outwardly extending portion of shaft 19. This eccentric gear meshes with sun gear 1 6. The pitch diameter of sun gear 1 6 is illustrated as being twice that of eccentric gear 21.

An eccentric 22 is fixed to shaft 19 and disposed between crank arms 17 and 1 8. A lift arm generally indicated at 23 has an inner end 24 rotatably mounted on eccentric 22 and an outer end 25 adapted to be connected to a driven member. The mid-portion 26 of arm 23 is curved so that, during movement of the lift arm between its extreme positions, the arm has a clearance space 27 which will avoid contact with the crank portion 28 on shaft 14 which connectsçrawnk arms 17 and 18.

The operation of unit 11 is shown in Figures 2 through 8. Starting from a position as shown in Figure 2 in which outer portion 25 of lift arm 25 is in its lowermost position, the center 29 of eccentric 22 will be in the position shown. Thus, portion 25 of arm 23, which is constrained to move along the vertical axis 31, will also be in its lowermost position. It should be noted that the space 27 formed by the curved nature of lift arm 23, and particularly portion 26 thereof, will permit the lift arm to clear the crank portion 28 which is mounted on shaft 14 and connects crank arms 17 and 18.

Upon rotation of shaft 14 and crank arms 1 7 and 18, 300 to the Figure 3 position, the planetary action of the gears will cause eccentric 22 to rotate an additional 600. This will cause upward travel of portion 25 of lift arm of 23. Upon rotation of the crank arms another 300 to the 600 position (Figure 4), eccentric 22 will have rotated an additional 1200. The rise of portion 25 of crank arm 23 will be more rapid than before.

When crank arms 1 7 and 18 reach their 900 position as shown in Figure 5, eccentric 22 will have rotated an additional 1800. The rate of rise from Figure 4 to Figure 5 will be slower than before since eccentric center 29 will be actually moving downwardly with respect to the axis of eccentric gear shaft 1 9.

As crank arms 17 and 18 move another 300 to the Figure 6 position, the outer end 25 of lift arm 23 will again move at a slower rate since eccentric center 29 continues to move downwardly with respect to the axis of shaft 1 9.

Moving to the Figure 7 position, another 30 for crank arms 17 and 18, eccentric center 29 will move upwardly with respect to axis of shaft 19.

Thus, the outer end 25 of lift arm 23 will be lifted at a relatively rapid rate. When the Figure 8 position is reached crank arms 17 and 1 8 will be in their uppermost position and so will the outer end 25 of lift arm 23. The rate of movement however will be somewhat slower than the last increment.

When it is desired to return lift arm 23 to its lowermost position, shaft 14 will be rotated in the opposite direction through coupling 1 5. The lift arm will follow the same path as before, slowing down at mid-stroke, and arrive at the position of Figure 2.

Figure 9 is a chart showing the variation in lift stroke from Figure 2 to Figure 8, that is, from the lowermost to the uppermost position of crank arms 1 7 and 18. The chart is equally applicable in the reverse direction. At constant rotational speed of shaft 14, the initial part of upstroke, indicated at 32, will be relatively rapid. At the mid portion, as indicated at 33, there will be a slow down or dwell period, and portion 34 of the position line shows a resumption of relatively rapid upward movement. In a typical construction, if the rate of movement at portion 34 is X inches per second, as designated by the circle 35, the rate of movement at portion 33 will be approximately X/7 inches per second.With the arrangementshown, the minimum velocity of the driven member in the area marked by the circle 37 will be located at approximately 46% of the total lift stroke, measured from the bottom. It will be understood that other arrangements are possible following the principles of the invention.

The path of center 29 of eccentric 22 is indicated by the line 36 in Figure 8. This locus is obtained by combining the movements of the crank arms with the planetary movement of gear 21 about gear 16.

Figure 10 shows the linkage system 11 applied to a press drive. The press is generally indicated at 38 and is shown as a simpler type of bottom drive hydraulic press having a base 39, pillars 41 and a table 42 which is lifted and lowered by mechanism 11. As illustrated, two mechanisms 11 are located side by side at the right hand end 43 of table 42, being driven by a common driving shaft 44 disposed between the two mechanisms.

A second pair of mechanisms 11 (not shown) are located at the left hand end of table 42, and are driven -in synchronism with the two mechanisms shown. Apertured clearance portions 45 of base 39 are provided. The outer ends 25 of lift arms 23 are apertured, as indicated at 46.

In operation of the embodiment of Figure 10, table 42 will be raised and lowered by mechanisms 11. At approximately the mid-point of each raising or lowering stroke, the table will be slowed down as described with respect to Figure 9.

Figure 11 shows another installation of mechanism 11 , this time as the lifting device in a stool type C frame knee. The knee is generally indicated at 48 and has a base 49 surmounted by a table 51. Four mechanisms 11 are disposed within base 49 and will operate in a manner similar to that described with respect to Figure 10.

Figure 1 2 shows a third type of installation, namely as a lifter mechanism for a cylinder operated automated parts conveyor. The unit is generally indicated at 52 and comprises a base 53 above which are disposed two cylinder operated reciprocable conveyor bars 54 in spaced parallel relation. These bars carry lugs 55 for transferring the workpieces (not shown). A table 56 is provided which is narrower than the space between bars 54, this table having workpiece locating lugs 57. Four mechanisms 11 are located at the four corners of table 56 and are connected thereto by depending brackets 58. During operation of units 11, table 56 will be moved between a lower position below the level of bars 54 and an upper position as shown in Figure 11 above these bars. The arrangement is such that the slowdown of table 56 will occur immediately before the workpiece is engaged, on the upstroke, and immediately before it is dropped onto bars 54 during the downstroke.

Claims (11)

Claims

1. A mid-point dwell linkage system comprising a fixed gear, a drive shaft rockable on the axis of said fixed gear, a crank arm fixed to said shaft, an eccentric gear rotatably mounted at the outer end of said crank and meshing with said fixed gear, an eccentric secured to and rotatable on the axis of said eccentric gear, and a lift arm having an inner end rotatably mounted on said eccentric and an outer end having means for connection to a driven member.

2. A linkage system according to claim 1, wherein said fixed gear comprises a sun gear.

3. A linkage system according to claim 1 or 2, wherein a second crank arm is secured to said shaft in spaced parallel relation with the first crank arm, said eccentric being disposed between said crank arms and said fixed gear being outside said crank arms.

4. A linkage system according to claim 1,2 or 3, further provided with pillow blocks supporting opposite ends of said shaft, said fixed gear and the or each crank arm being disposed between said pillow blocks.

5. A linkage system according to any preceding claim, wherein the lift arm is of curved construction whereby it will not interfere with said shaft during rotation.

6. A linkage system according to any preceding claim, wherein the pitch diameter of the fixed gear is twice that of the eccentric gear.

7. A linkage system according to any preceding claim, in combination with a second such dwell linkage system with the drive shafts of said two systems being coaxial with a common shaft between and coupled to said drive shafts providing a driving connection between them.

8. A lift table assembly comprising two pairs of linkage systems according to claim 7, two linkage systems having a common drive shaft being connected to one end of said table, and the second pair of linkage systems being arranged symmetrically opposite said first pair and connected to the other end of the table.

9. A mid-point dwell linkage system comprising a pair of pillow blocks, a rockable shaft supported by and extending between said pillow blocks, a drive coupling on said shaft, a fixed sun gear concentric with said shaft inside one of said pillow blocks, a pair of spaced parallel crank arms secured to said shaft between said fixed gear and the other pillow block, an eccentric gear shaft rotatably mounted at the outer ends of said crank arms, an eccentric gear of substantially smaller diameter than said sun gear secured to said eccentric gear shaft and meshing with said sun gear, an eccentric fixed to said eccentric gear shaft between said crank arms, a lift arm having an inner end rotatably mounted on said eccentric, said lift arm being of curved construction between said inner and outer ends, whereby said lift arm will clear said drive shaft during movement between extreme positions, and a driven member secured to the outer end of said lift arm.

10. A mid-point dwell linkage system constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

11. Lifting or press apparatus embodying the linkage system of any one of claims 1 to 7, claim 9 or claim 10.