Abstract

This paper studies a structural–parametric synthesis of the four-bar and Stephenson II, Stephenson III A, and Stephenson III B six-bar function generators. A four-bar function generator is formed by connecting two coordinate systems with given angles of rotation using a negative closing kinematic chain (CKC) of the RR type. Six-bar function generators are formed by connecting two coordinate systems using two CKCs: a passive CKC of the RRR type and a negative CKC of the RR type. The negative CKC of the RR type imposes one geometrical constraint to the relative motion of the links, and its geometric parameters are defined by least-squares approximation. Passive CKC of the RRR type does not impose a geometrical constraint, and the geometric parameters of its links are varied to satisfy the geometrical constraint of the negative CKC. Numerical results of the four-bar and six-bar function generators parametric synthesis are presented.

1 Introduction

The first studies on the design of function-generating linkages are due to Svoboda [1,2], who designed a Watt II function generator for the generation of the logarithmic function. Kinematic synthesis (dimensional or parametric synthesis) of mechanisms, including function-generating linkages, is carried out on the basis of the kinematic geometry of finite positions of a rigid body, approximation methods (polynomials), and computers [3]. The kinematic geometry of finite positions of a rigid body, which in the case of plane motion is known as the Burmester theory [4], is used for the synthesis of function generators in the works of Hunt [5], Bottema and Roth [6], Angeles and Bai [7,8], Pira and Cunaku [9], McCarthy and Soh [10], and others. The synthesis of mechanisms by kinematic geometry is clear and simple. However, these methods are applicable for a limited number of positions. For the kinematic synthesis of mechanisms with unlimited positions of the output links, the approximation methods are used, the foundations of which were laid by Chebyshev [11]. Approximation (algebraic, optimization) methods for the kinematic synthesis of four-bar and six-bar function generators Watt II, Stephenson II, and Stephenson III were used in the works of Freudenstein [12], Hartenberg and Denavit [13], McLarnan [14], Subbian and Flugrad [15,16], Kiper et al. [17], Hwang and Chen [18], Bulatovic et al. [19], Plecnik and McCarthy [2022], and others. In Refs. [18,19,20], the polynomial homotopic software bertini [23] was used. At the intersection of kinematic geometry and approximation synthesis, a new direction in the kinematic synthesis of mechanisms—approximation kinematic geometry—has been created by Sarkissyan et al. [2426]. Approximation kinematic geometry combines the advantages of methods of kinematic geometry and approximate synthesis of mechanisms, such as simplicity and unlimited positions of the output links. Based on approximation kinematic geometry by Baigunchekov et al. [2731], the parallel mechanism and manipulator are synthesized.

In this work, a structural–parametric synthesis of four-bar and six-bar function generators is carried out, where the structures and geometric parameters of the links of the synthesized mechanisms are determined in arbitrary given discrete values of the input and output link angles. In structural–parametric synthesis, according to the given laws of motion of the input and output links, structural schemes and geometric parameters of the links of the synthesized mechanisms are simultaneously determined. At the same time, the structural–parametric synthesis of the designed mechanisms begins with the smallest number of links and becomes more complicated depending on the implementation of the specified laws of motion of the output links within the required accuracy. Depending on the complexity of the given laws of motion of the output links, it is possible to form mechanisms with complex structural schemes. Structural and kinematic analysis of complex mechanisms containing Assur groups of higher classes [32] is the subject of work [3341]. In this paper, to analyze the positions of complex mechanisms, which is necessary to evaluate the results of parametric synthesis, a simple method of conditional generalized coordinates is proposed.

2 Structural Synthesis of the Planar Four-Bar and Six-Bar Function Generators With Revolute Joints

According to the developed principle of mechanism formation, they are formed by connecting the output object to the base using active, passive, and negative CKCs [27,28]. Active CKCs have active joints, passive CKCs have zero DOF, and negative CKCs have negative DOF. The active and passive CKCs impose geometrical constraints on the motion of the output object. The passive CKCs do not impose geometrical constraints.

The output object of the function generators is a link that performs a given rotary or translational motion relative to the base at a given motion of the input link. Let the input link and the output object perform rotational movements. We choose as the input and output links the coordinate systems Ax1y1 and Bx2y2 rotating relative to the base with rotation angles φi and ψi (Fig. 1(a)).

Fig. 1
Structural synthesis of planar function generators
Fig. 1
Structural synthesis of planar function generators
Close modal

If we connect the planes of two moving coordinate systems Ax1y1 and Bx2y2 by a negative CKC CD of the RR type, then we obtain a structural scheme of a four-bar function generator ACDB. Connection of the planes of two moving coordinate systems Ax1y1 and Bx2y2 by binary link CD of the type RR is possible when the plane of the moving coordinate system Bx2y2 has a circular point (a point moving along a circle) D in relative motion to the coordinate system Ax1y1, or vice versa, i.e., when there is a circular point C in the plane of the coordinate system Ax1y1 in relative motion with respect to the coordinate system Bx2y2.

If none of the planes of the moving coordinate systems Ax1y1 and Bx2y2 do not have circular points in relative motion, then the planes of the two coordinate systems are connected by passive CKC CED of the RRR type. As a result, we obtain a structural scheme of the five-bar linkage ACEDB with two DOF (Fig. 1(b)). To form six-bar function generators from this five-bar linkage, we connect its non-adjacent links by binary link FG of the type RR, having one negative DOF (or a constraint that reduces the DOF of the system by one), defined by the Chebyshev formula

(1)
where n = 1 is the number of moving links, p5 = 2 is the number of kinematic pairs of the fifth class, then F = −1.

Consequently, the negative CKC FG, imposing one geometrical constraint on the five-bar linkage with two DOF, forms six-bar function generators with one DOF. Figures 1(c)1(f) show the structural schemes of the formed six-bar function generators. If links 1 and 2 of the five-bar linkage are connected by binary link FG, we obtain a Stephenson I function generator (Fig. 1(c)). If links 3 and 2 of the five-bar linkage are connected by binary link FG, we obtain a Stephenson II function generator (Fig. 1(d)). When link 3 of the five-bar linkage is connected to the base by binary link FG, we obtain a Stephenson III A function generator (Fig. 1(e)). When link 4 of the five-bar linkage is connected to the base by binary link FG, we obtain a Stephenson III B function generator (Fig. 1(f)).

3 Parametric Synthesis of Four-Bar Function Generator

Let given the function
(2)
of the four-bar function generator (Fig. 2), where N is the number of finite positions of the moving planes Ax1y1 and Bx2y2.
Fig. 2
Four-bar function generator
Fig. 2
Four-bar function generator
Close modal
It is necessary to determine the synthesis parameters (geometric parameters) of the four-bar function generator that implements function (2). The synthesis parameters are xC(1),yC(1),xD(2),yD(2) and lCD, where xC(1),yC(1) and xD(2),yD(2) are the coordinates of the joints C and D in coordinate systems Ax1y1 and Bx2y2, respectively, and lCD is the length of the CD link. Consider the movement of the coordinate system Bx2y2 relative to the coordinate system Ax1y1. In this case, point D moves along a circle centered at point C and with radius lCD. Derive an equation
(3)
where
(4)
(5)
Equation (3) is an equation of geometrical constraint imposed by binary link CD of the type RR on the movements of two moving coordinate systems Ax1y1 and Bx2y2. The left side of Eq. (3) will be denoted by Δqi and called the weighted difference function
(6)
Parametric synthesis of a four-bar function generator is to determine five geometric parameters xC(1),yC(1),xD(2),yD(2),andlCD from the minimum of function (6). Substituting expressions (4) and (5) into Eq. (6), we obtain
(7)
If we introduce the notations
then Eq. (7) takes the form
(8)
Equation (8) is linear in the following two groups of synthesis parameters:
(9)
and is represented in two linear forms
(10)
and
(11)
If the following notations are introduced
where
then Eqs. (10) and (11) take the form
(12)
To determine the vectors p(k) of synthesis parameters, we minimize function (12) by least-square optimization, i.e., derive the sums
(13)
and consider the necessary conditions for the minimum of function (13) over two groups of synthesis parameters p(k)
(14)
and
(15)
Conditions (14) and (15) lead to the following two systems of linear equations for two groups of synthesis parameters:
(16)
and
(17)
where
(18)
(19)

It is easy to show that the Hessian of matrices D(1) and D(2) are positive definite together with the principal minors [23], and then the solutions of the systems of linear Eqs. (16) and (17) correspond to the minimum of function (13). Therefore, for given values of the vector parameters p(2) = [p4, p5, p3], the vector parameters p(1) = [p1, p2, p3] are determined by solving the system of linear Eq. (16). Based on the obtained values of the vector parameters p(1), the vector parameters p(2) are determined by solving the system of linear Eq. (17). In this case, the sequence of function S(k) values will be decreasing and have a limit as a sequence bounded from below. This allows using the linear iteration method based on kinematic inversion to solve the least-square approximation.

4 Parametric Synthesis of Six-Bar Function Generators

Parametric synthesis of six-bar function generators (Figs. 1(c)1(f)) consists of the parametric synthesis of the passive CKC CED and the negative CKC FG. Synthesis parameters of the passive CKC CED of all six-bar function generators are xC(1),yC(1),xD(2),yD(2),lCE,andlED, where xC(1),yC(1) and xD(2),yD(2) are the coordinates of the joints C and D in the coordinate systems Ax1y1 and Bx2y2 of the links 1 and 2, respectively, lCE and lED are the lengths of the CE and ED links. Since the passive CKC CED of the type RRR has zero DOF, it does not impose a geometrical constraint on the motion of the coordinate systems Ax1y1 and Bx2y2. Geometric parameters of the passive CKC CED links are varied, and the synthesis parameters of the negative CKC FG are approximated. For the parametric synthesis of the Stephenson I (Fig. 1(c)), Stephenson II (Fig. 1(d)), Stephenson III A (Fig. 1(e)), and Stephenson III B (Fig. 1(f)) function generators, we determine the positions of the links CE and ED of the passive CKC CED by the equations
(20)
(21)
where
(22)
(23)
(24)
(25)

Synthesis parameters for the negative CKC FG of the Stephenson I mechanism (Fig. 1(c)) are xF(1),yF(1),xG(2),yG(2),andlFG, which are determined similar to the parametric synthesis of the four-bar function generator (Fig. 2). Therefore, the functionality of the Stephenson I mechanism is the same as the functionality of the four-bar function generator.

Synthesis parameters for the negative CKC FG of the Stephenson II function generator (Fig. 3) are xF(3),yF(3),xG(2),yG(2),andlFG, where xF(3),yF(3) and xG(2),yG(2) are the coordinates of the joints F and G in the coordinate systems Cx3y3 and Bx2y2 of the links 3 and 2, respectively.

Fig. 3
Stephenson II function generator
Fig. 3
Stephenson II function generator
Close modal
For parametric synthesis of the link FG, we consider the movement of the coordinate system Bx2y2 relative to the coordinate system Cx3y3 and derive the equation of geometrical constraint
(26)
where
(27)
(28)

Further, the synthesis parameters of the link FG are determined similarly to the determination of synthesis parameters of the link CD of the four-bar function generator.

Synthesis parameters of the binary link FG of the Stephenson III A function generator (Fig. 4) and the Stephenson III B function generator (Fig. 5) are xF(3),yF(3) and xF(4),yF(4), respectively, and XG,YG,andlFG are for both function generators, where xF(3),yF(3) and xF(4),yF(4) are the coordinates of the joint F in the coordinate systems Cx3y3 and Dx4y4, respectively, XG and YG are the coordinates of the joint G in the absolute coordinate system OXY.

Fig. 4
Stephenson III A function generator
Fig. 4
Stephenson III A function generator
Close modal
Fig. 5
Stephenson III B function generator
Fig. 5
Stephenson III B function generator
Close modal
For parametric synthesis of the link FG of the Stephenson III A and Stephenson III B function generators, we derive the following geometrical constraint equation:
(29)
where for the Stephenson III A function generator
(30)
for the Stephenson III B function generator
(31)

Further, synthesis parameters of the binary link FG are determined similar to the parametric synthesis of the four-bar function generator.

5 Numerical Results

Let us consider the parametric synthesis of the four-bar, Stephenson II, Stephenson III A, and Stephenson III B function generators. The following coordinates XA = 10.0, YA = 20.0, XB = 70.0, and YB = 20.0 of the four-bar Stephenson II, Stephenson III A, and Stephenson III B function generators pivots A and B are given in the absolute coordinate system OXY.

5.1 Four-Bar Function Generator.

Table 1 gives the values of the angles φi and ψi of the input and output links for N = 12 of the four-bar function generator (Fig. 6).

Fig. 6
Four-bar function generator with scale size
Fig. 6
Four-bar function generator with scale size
Close modal
Table 1

The values of the angles φi and ψi of the four-bar function generator

N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi36 deg38 deg51 deg69 deg88 deg102 deg108 deg108 deg104 deg98 deg84 deg57 deg
N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi36 deg38 deg51 deg69 deg88 deg102 deg108 deg108 deg104 deg98 deg84 deg57 deg

Table 2 presents the obtained values of the synthesis parameters of the four-bar function generator.

Table 2

The values of the synthesis parameters of the four-bar function generator

xC(1)yC(1)xD(2)yD(2)lCD
25.98015.00825.00743.30045.012
xC(1)yC(1)xD(2)yD(2)lCD
25.98015.00825.00743.30045.012
To check the parametric synthesis results of the four-bar function generator, values of the angle ψi corresponding to the values of the angle φi are determined by the equation
(32)
where
(33)
(34)
(35)
In the expressions (33) and (34), coordinates of the joint С in the absolute coordinate system OXY are determined by the equation
(36)

Table 3 presents the obtained values of the angle ψi, and Fig. 7 shows a graph of its change.

Fig. 7
Graph of the angle ψi change of the four-bar function generator
Fig. 7
Graph of the angle ψi change of the four-bar function generator
Close modal
Table 3

The obtained values of the angle ψi

N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi36.17 deg37.60 deg51.30 deg69.09 deg88.10 deg102.32 deg
N789101112
φi180 deg21002400270030003300
ψi107.91 deg107.71 deg104.44 deg97.67 deg83.77 deg57.27 deg
N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi36.17 deg37.60 deg51.30 deg69.09 deg88.10 deg102.32 deg
N789101112
φi180 deg21002400270030003300
ψi107.91 deg107.71 deg104.44 deg97.67 deg83.77 deg57.27 deg

5.2 Stephenson II Function Generator.

Table 4 gives the values of the angles φi and ψi of the input and output links for N = 12 of the Stephenson II function generator (Fig. 8).

Fig. 8
Stephenson II function generator with scale size
Fig. 8
Stephenson II function generator with scale size
Close modal
Table 4

The values of the angles φi and ψi of the Stephenson II function generator

N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi104 deg98 deg93 deg90 deg90 deg92 deg98 deg105 deg112 deg116 deg116 deg111 deg
N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi104 deg98 deg93 deg90 deg90 deg92 deg98 deg105 deg112 deg116 deg116 deg111 deg

Table 5 presents the obtained values of the synthesis parameters of the Stephenson II function generator.

Table 5

The values of the synthesis parameters of the Stephenson II function generator

xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)xG(2)yG(2)lGF
8.6585.00345.98350.01712.49621.64523.775−7.72520.71513.97540.211
xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)xG(2)yG(2)lGF
8.6585.00345.98350.01712.49621.64523.775−7.72520.71513.97540.211

To check the parametric synthesis results of the Stephenson II function generator, we determine the values of the angle ψi corresponding to the values of the angle φi. To do this, the positions of the Stephenson II function generator are analyzed.

Stephenson II function generator contains an input link 1 and an Assur group of the fourth class. It has the following structural formula:
(37)
For position analysis of the Stephenson II function generator or the mechanism of the fourth class, a simple method of conditional generalized coordinate is proposed, which is the opposite of the method of structural synthesis. If we remove a negative CKC—a binary link FG of the type of RR by disconnecting the elements of the joints F and G—then the considered mechanism acquires one additional DOF. If we take the link 2 as a conditional input link and the angle ψi as a conditional generalized coordinate, then this mechanism of the fourth class is transformed into a mechanism of the second class with the structural formula
(38)
For a given value of the angle φi and in changing the value of the conditional generalized coordinate ψi, the distance between the centers of the disconnected joints F and G is changed. A residual function is derived below:
(39)
where l(FG)i* is a variable distance between the centers of the joints F and G, which is determined by the equation
(40)
Coordinates of the joints F and G in Eq. (40) are determined by the expressions
(41)
(42)
where
(43)
To determine the angle φ3i in Eq. (41), we analyze the positions of the dyad II (3,4) and obtain
(44)
where
(45)
(46)
(47)

Consequently, the residual (39) is a function of the conditional generalized coordinate ψi. Minimizing this function by the bisection method, we obtain the values of the angle ψi for a given value of the angle φi. By changing the values of the angle φi, we similarly find the corresponding values of the angle ψi.

Table 6 presents the obtained values of the angle ψi, and Fig. 9 shows a graph of its change.

Fig. 9
Graph of the angle ψi change of the Stephenson II function generator
Fig. 9
Graph of the angle ψi change of the Stephenson II function generator
Close modal
Table 6

The obtained values of the angle ψi

N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi104.12 deg98.35 deg93.18 deg90.24 deg89.54 deg92.07 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi97.57 deg105.21 deg111.87 deg116.16 deg115.75 deg110.83 deg
N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi104.12 deg98.35 deg93.18 deg90.24 deg89.54 deg92.07 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi97.57 deg105.21 deg111.87 deg116.16 deg115.75 deg110.83 deg

5.3 Stephenson III A Function Generator.

Table 7 gives values of the angles φi and ψi of the input and output links of the Stephenson III A function generator (Fig. 10).

Fig. 10
Stephenson III A function generator with scale size
Fig. 10
Stephenson III A function generator with scale size
Close modal
Table 7

The values of the angles φi and ψi of the Stephenson III A function generator

N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi11 deg03 deg07 deg15 deg24 deg33 deg44 deg57 deg71 deg83 deg77 deg43 deg
N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi11 deg03 deg07 deg15 deg24 deg33 deg44 deg57 deg71 deg83 deg77 deg43 deg

Table 8 presents the obtained values of the synthesis parameters of the Stephenson III A function generator.

Table 8

The values of the synthesis parameters of the Stephenson III A function generator

xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)XGYGlGF
12.9797.50345.94740.01416.97129.43823.775−7.72539.98321.08724.897
xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)XGYGlGF
12.9797.50345.94740.01416.97129.43823.775−7.72539.98321.08724.897
To check the parametric synthesis results of the Stephenson III A function generator, let us determine the values of the angle ψi corresponding to the values of the angle φi. To do this, we analyze the positions of the Stephenson III A function generator. This function generator has a structural formula
(48)
i.e., it belongs to the second class mechanism. Therefore, it is necessary to consistently solve the position problems of the dyads CFG and EDB.
From the position analysis of the dyad CFG, we obtain
(49)
(50)
where
(51)
(52)
Based on the obtained values of the angle φ(CF)i, we determine the value of the angle φ3i
(53)
and the coordinates of the joint E
(54)
where
(55)
Then, we solve the position problem of the dyad EDB and determine the value of the angle ψi
(56)
where
(57)
(58)
(59)

Table 9 presents the obtained values of the angle ψi, and Fig. 11 shows a graph of its change.

Fig. 11
Graph of the angle ψi change of the Stephenson III A function generator
Fig. 11
Graph of the angle ψi change of the Stephenson III A function generator
Close modal
Table 9

The obtained values of the angle ψi

N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi11.21 deg02.98 deg06.87 deg14.91 deg23.93 deg33.16 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi43.70 deg57.01 deg70.96 deg82.91 deg77.04 deg42.83 deg
N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi11.21 deg02.98 deg06.87 deg14.91 deg23.93 deg33.16 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi43.70 deg57.01 deg70.96 deg82.91 deg77.04 deg42.83 deg

5.4 Stephenson III B Function Generator.

Table 10 gives the values of the angles φi and ψi of the input and output links of the Stephenson III B function generator (Fig. 12).

Fig. 12
Stephenson III B function generator with scale size
Fig. 12
Stephenson III B function generator with scale size
Close modal
Table 10

The values of the angles φi and ψi of the Stephenson III B function generator

N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi223 deg244 deg266 deg264 deg245 deg240 deg245 deg256 deg268 deg267 deg245 deg221 deg
N123456789101112
φi0 deg30 deg60 deg90 deg120 deg150 deg180 deg210 deg240 deg270 deg300 deg330 deg
ψi223 deg244 deg266 deg264 deg245 deg240 deg245 deg256 deg268 deg267 deg245 deg221 deg

Table 11 presents the obtained values of the synthesis parameters of the Stephenson III B function generator.

Table 11

The values of the synthesis parameters of the Stephenson III B function generator

xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)XGYGlGF
12.9787.49355.01729.9627.50713.00415.02910.13439.99519.91725.545
xC(1)yC(1)lCElEDxD(2)yD(2)xF(3)yF(3)XGYGlGF
12.9787.49355.01729.9627.50713.00415.02910.13439.99519.91725.545
Let us determine the values of the angle ψi corresponding to the values of the angle φi. To do this, we analyze the positions of the Stephenson III B function generator. This function generator has a structural formula
(60)
i.e., it belongs to the mechanism of the third class. For position analysis of this mechanism, we remove the negative CKC FG by disconnecting the elements of the joints F and G. Then, the considered mechanism acquires one additional DOF. If we take link 2 as a conditional input link, due to the appeared DOF, then the third class mechanism is transformed into the second class mechanism with structural formula (38).
Let us derive a residual function of the form (39), where the coordinates of the joint F are determined by the equation
(61)
To determine the angle φ4i in Eq. (61), we solve a position analysis problem of the dyad CED and obtain
(62)
where
(63)
(64)

Consequently, the residual (39) is a function of the conditional generalized coordinate ψi. Minimizing this function by the bisection method, we obtain the values of the angle ψi. Table 12 presents the obtained values of the angle ψi, and Fig. 13 shows a graph of its change.

Fig. 13
Graph of the angle ψi change of the Stephenson III B function generator
Fig. 13
Graph of the angle ψi change of the Stephenson III B function generator
Close modal
Table 12

The obtained values of the angle ψi

N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi223.29 deg244.38 deg265.81 deg264.01 deg245.44 deg240.18 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi244.96 deg255.87 deg267.45 deg267.04 deg244.83 deg220.71 deg
N123456
φi0 deg30 deg60 deg90 deg120 deg150 deg
ψi223.29 deg244.38 deg265.81 deg264.01 deg245.44 deg240.18 deg
N789101112
φi180 deg210 deg240 deg270 deg300 deg330 deg
ψi244.96 deg255.87 deg267.45 deg267.04 deg244.83 deg220.71 deg

6 Conclusion

Structural synthesis of four-bar and six-bar function generators with revolute joints has been carried out. A four-bar function generator is formed by connecting two rotating coordinate systems with given rotation angles using a binary link of the type RR, which is a negative CKC that imposes one geometrical constraint. Six-bar function generators are formed by connecting these two rotationally moving coordinate systems using a passive CKC of the type RRR and by connecting non-adjacent links of the resulting five-bar linkage by binary link of the type RR. As a result, Stephenson I, Stephenson II, Stephenson III A, and Stephenson III B function generators have been formed. Passive CKC of the type RRR does not impose a geometrical constraint on the movement of two moving coordinate systems, and its geometric parameters are varied to satisfy the constraint of the negative CKC. Geometric parameters of the negative CKC of the type RR are determined by least-square approximation. In this case, the least-square approximation problem is reduced to a simple kinematic inversion problem based on linear iteration. Structural and parametric synthesis of the four-bar and six-bar function generators are carried out simultaneously, starting with the smallest number of links of CKCs. Numerical results of parametric synthesis of four-bar and six-bar function generators are presented.

Acknowledgment

This work was funded by the Science Committee of the Ministry of Science and High Education of Kazakhstan (Grant No. AP14872115 “Development and Research of the Novel Tripod Type Parallel Manipulators With Six Degrees of Freedom”).

Conflict of Interest

There are no conflicts of interest.

Data Availability Statement

The datasets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.

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