This invention is concerned with maintaining a selected ratio between multiple, independently ' changeable operating parameters ^' of a control system such as those associated with a camera zoom lens sys¬ tem. These ratios are normally difficult to inter¬ relate, especially where the functional relationship between each control input and its operational para- ^' meter is different for the different operational para¬ meters. One instance where it is desirable to inter¬ relate these parameters is the object distance para¬ meter and the focal length parameter of a camera zoom lens in order to keep the image size from the lens system constant even through the distance between the subject being photographed and the lens system va¬ ries. II. BACKGROUND ART

It is desirable on occasion to interrelate the normally independently controlled operating parame¬ ters of a control system so as to automatically main¬ tain selected ratios between the operating parameters as any one of the parameters is changed. One such control system in which this feature is desired is a zoom lens for a camera where the maintenance of a con¬ stant image size is desired even through the distance between the lens and the subject being photographed is chs-nging.

With respect to zoom lens, the prior art has attempted to interrelate the object distance parame¬ ter used to focus the lens and the focal length para¬ meter used to zoom the lens through the use of cams with non-logarithmic camming surface so as to main¬ tain a fixed ratio between the object distance para- meter and the focal length parameter of the lens.

- 2 -

Such systems prevented the zoom lens from teing effec¬ tively used as a conventional zoom lens where the ob¬ ject distance parameter is controllable independently of the focal length parameter and also was unable to interrelate the operating parameters at different de¬ sired ratios. The prior art has further attempted to permit interrelating the object distance parameter with the focal length parameter b providing an object distance control member whose rotational movement was logarithmic of the actual value of the object dis¬ tance parameter set by the object distance control member and by providing a focal length control member whose rotational movement was logarithmic of the ac¬ tual value of the focal length parameter set by the focal length control member. The object distance control member and the focal length control member are rotatably mounted about a common rotational axis so that the operator may manually hold and rotate both control members simultaneously to ^" maintain con- stant ratios between the object distance setting and focal length setting of the lens. Such systems de¬ pended on the ability of the operator to manually hold and turn the control members and required com¬ plex internal constructions to correlate the control member movement with the setting of ^" the operating parameter. Such systems also caused a loss of effec¬ tively obtainable accuracy in certain settings of the lens. III. SUMMARY OF THE INVENTION According to the present invention, there is pro¬ vided an interlock mechanism for an operating system with a plurality of independently controllable opera¬ ting parameters comprising sending means for genera¬ ting control outputs which correspond to the loga- rithmic value to a common base of the respective

actual values of the different operating parameters; and control means operatively connected to the sending means and responsive to the difference between the control outputs to change the actual values of the operating parameters in response to a change in the actual value of one of the operating parameters to maintain a selected difference between the control out¬ puts so that a prescribed ratio is maintained between the actual values of the operating parameters. Embo- diments of the invention are illustrated applied to a camera zoom lens to interrelate the object distance parameter and focal length parameter of the lens with¬ out the requirement of special internal lens construc¬ tion. Electromechanical, mechanical and electrical versions of the interlock mechanism are illustrated. The control means of the interlock mechanism is ad¬ justable to permit different ratios to be selectively maintained between the operational control parameters of the operating system. The control outputs of the electromechanical ver¬ sion of the interlock mechanism are electrical vol¬ tages whose values are respectively representative of the logarithmic value to a common base of the actual value of the operating parameter with which the con- trol output is associated. The control means of the electromechanical version includes an adjustment mechanism for selectively adding selected voltage values to certain of the voltage outputs to generate apparent voltage outputs with the control means re- sponsive to any difference between one of the voltage outputs to change the actual value of the operating parameters in response to a change in the actual value of one of the operating parameters until one of the voltage outputs equals the apparent voltage outputs so that prescribed ratios are maintained between the

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actual values of the operating parameters.

The control outputs of the mechanical version of the interlock mechanism are the parallel linear move¬ ments of output members where the amount of linear movement of each of the output members corresponds to the logarithmic value to a common' ase of the actual value of the operating parameter with which the out¬ put member is associated. The control means of the ^• mechanical version includes interconnecting means for selectively locking the output members together so that movement of one of the output members as its associated operating parameter is changed causes a like movement in the other of the output members to change the operating parameter associated with each so that the selected prescribed ratio is maintained between the operating parameters.

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IV. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partial side elevational view of a camera zoom lens on which a first embodiment of the invention is incorporated; Fig. 2 is an electrical schematic of the control circuit associated with the invention seen in Fig. 1;

Fig. 3 is a composite graph illustrating the operation of the invention of Fig. 1;

Fig. 4 is a perspective view of a second e bodi- ment of the invention;

Fig. 5 is a plane view of a third embodiment of the invention; and

Fig. 6 is an electrical schematic for the embo¬ diment of the invention of Fig. 5.

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V. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The invention of this application is disclosed as applied to the power zoom lens L _pz of a movie camera C in Figs. 1-3, to a nonpowered zoom lens L- of a still camera B^ in Fig. 4 and to a three variable con¬ trol system in Figs. 5 and 6. The invention can like¬ wise be applied to a wide variety of systems which have two or more. independently variable control para¬ meters. Va. First Embodiment

In Figs. 1-3, the lens L _pz has a conventional manually operated object distance (focus) control mem¬ ber CM ₀₁ , and a conventional power or manually operated focal length (zoom) control member CM _pτ rotatably mounted on lens body B, about lens axis A _τ . Camera body B _MC mounts the reversible motor drive unit MDU to selectively power control member CM _τ through gears G _j ,. An interlock control mechanism 10 with an object distance sending unit 11 and a focal length sending unit 12 controlling a ratio base control unit 14 powered through switch SW, and adjusted with selector knob 15. automatically maintains any selected ratio between object distance and focal length.

The camming surface 26 on an object distance cam 25 carried by control member CM _oπ axially displaces a spring urged drive rod 21 to adjust the movable con¬ tact P _QTV J of a linear potentiometer assembly 20 in sending unit 11 via a cam follower roller 24 in roller assembly 22 on drive rod 21 as control member CM.-.,, is rotated to adjust the object distance parameter and focus lens L _p „. Similarly, the camming surface 36 on a focal length cam 35 carried by control member CMp _L axially displaces a spring urged drive rod 31 to ad¬ j ^•> ust the movable contact P,F,L,-,M; of a linear p ^~ otentio- meter assembly 30 in sending unit 12 via a cam follower

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roller 34 in roller assembly 32 on drive rod 31 as control member CM-, is rotated to adjust the focal length parameter of lens L . The shape of the object distance camming surface 26 is logarithmic of th'e va- lues of the object distance parameter to which the lens can be set so that the voltage output at the mo¬ vable contact P _orj _ _j on potentiometer assembly 20 is the logarithm to a common base of the value of the object distance parameter to which the lens is set. Thus, the drive rod 21 is axially displaced a varia¬ ble distance d from the base object distance refe¬ rence plane AP _QD over the total distance range d _Q of the camming surface 26 while the drive rod 31 is axially displaced a variable distance d, from the base focal length object distance plane AP _pτ over the total distance range d _pτ of the camming surface 36.

The distance da„ is the log ^a arithmic value of the actual value to which the control member CM _nr) has set the object distance parameter of the lens while the dis¬ tance d, is the logarithmic value of the actual value to which the control member CM, F,,L, has set the focal length control parameter of the lens. The distances d and d, can be determined by the following equa¬ tions: d = K log actual object distance value x smallest object distance value _d = K _l nσ actual focal length value ■b ^x smallest focal length value where x is any convenient base for the logarithm and where K is a constant. While the actual control parameter values may be used in the calculations, di¬ viding the actual control parameter value by the smallest control parameter value in its operation range facilitates such calculations by allowing the camming surfaces 26 and 36 to

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start at "0" for graphing purposes. The shape of the camming surface 26 corresponds to the focal length curve in Fig. 3 while the shape of camming surface 36 corres¬ ponds to the object distance curve. The shape o ^' f the camming surfaces 26 and 36 are also adjusted for any axial movement of the control members CM _QD and CMp, during adjustment.

As seen in Fig. 2, the control circuit for the interlock mechanism 10 interfaces with the already existing circuitry in the motor drive unit MDU. The conventional motor drive circuitry is seen in the upper portion of the schematic with a battery BAT,,, speed switch S _t , _p , a pair of zoom switches SW--. and S _ZI controlled by actuator 45 (Fig- 1) _> and a reversible drive motor M _pT to selectively rotate control member CM _pτ . This circuit is modified by connecting the switches SW and SW-,. to motor Mp _L through the common contact and the contact shown open in Fig. 2 of selec¬ tor switches SW,, and SW, ₂ respectively in gang switch SW _j . Thus, when switches SW _I3 and SW,.- in Fig. 2 are transferred, the switches S ~ _Ω and S „ _T operate motor Mp, in conventional manner.

The ratio control unit 14 is powered by a battery BAT, through switch SW,., to produce a regulated B+ out- put. The fixed resistance of potentiometer P.,,, in sen¬ ding unit 11 is connected to the B+ output through re¬ sistance R2 and to ground through resistance R3. The fixed resistance of potentiometer Pp _L in sending unit 12 is connected to the B+ output through potentiometer V . m of ganged potentiometer assembly P. and to ground through potentiometer P.- of assembly P. where control knob 15 operates potentiometers P., and P.- so that their effective resistances at any setting sum to the maximum resistance of each potentiometer. The voltage output 0 _QD at the movable contact of

potentiometer P _CD is connected to opposite sign inputs of a pair of comparators CP- _j . and CP _n while the voltage output 0p _L at the movable contact of potentiometer Pp _L is connected to the other opposite sign inputs to the 5 comparators. Cross biasing is provided with resistor R4. The output of comparator CP _Q - drives the coil of relay RY _fl while the output of comparator CP _j drives the coil of relay RY, . The normally open contacts of re¬ lay RY _Q drive the motor Mpγ in a.first direction

10. through switch SW.,., while the normally open contacts of relay RY-. drive the motor Mp, in the opposite direction through switch SW, ₂

The ganged potentiometer assembly P. controls the ratio which is to be maintained between the value of

15 the object distance parameter versus the value of the focal length parameter. The comparators CP _T and CP _Q drive the motor Mp,. to shift the value of the focal • length parameter until the voltage output from the mo¬ vable contact of potentiometer P _pL equals the voltage

20 output from the movable contact of potentiometer P.,,, In effect, this is maintaining the apparent difference in the logarithmic equivalent of the object distance value and the logarithmic equivalent of the focal length value ^' at zero as seen by the comparators CP- _j - and

25 CP _Q . In effect, the ganged potentiometer assembly P. is used to raise or lower the apparent focal length voltage output by a constant amount at each setting of the ganged potentiometer assembly P..

Because there is a relationship between the resis-

30 tive values of the potentiometers P _nι ->, P _pT , P _A τ ^anc ^ and the resistors R2 and R3, choosing the resis¬ tive values of the fixed resistances of potentiometers P _QD and P _p . as equal simplifies the determination of the remaining resistive values. The relationship is

35 further simplified when the resistive values of resis--

tors R2 and R3 are each selected as equal to the resis¬ tive value of the fixed resistance of potentiometer _Qγ . or P _p , and this is the case in this application. For illustration purposes, say the resistive value of the fixed resistances of potentiometers P _0D and Ppγ as well as resistors R2 and R3 is selected as "R".

It will be further noted that the fixed resis¬ tances of the potentiometers P., and P _ft2 are selected as equal to each other to give proper voltage output curve shift. Under these conditions, it will be seen that, if full ^' range of operation of the controls is de¬ sired, then the resistive value of each of potentio¬ meters P., and P« ₂ is limited to a range of "R" to "2R". In one limiting case, that illustrated in the drawings, the resistive value of each potentiometer P., and P. ₂ is selected as "2R ^M and one end of the fixed resistance in each is left open or unconnected. In the other limiting case (not shown in the drawings) , the resistive value of each potentiometer P., and P. ₂ would be "R" and those ends of the fixed resistances shown unconnected in the drawings would be shorted to each other. Because selecting the value for potentio¬ meters P., and _A2 at "R" results in maximum circuit current drain while selecting the value at "2R" re- suits in minimum circuit current drain, the value selected in the illustrated circuit is "2R". In the case where the resistive value of potentiometers P., and P _A2 is selected somewhere between the limiting values of "R" and "2R", then some calculated resis- tance would be placed between the unconnected ends of the fixed resistances of the potentiometers P., and

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As seen in Fig. 3, the output 0 _QD (Fig. 2) of the object distance sending unit 11 is. the voltage equivalent of the logarithmic value of the value to

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which the control member CM _nn has set the object dis¬ tance parameter while the output O _p , (Fig. 2) of the focal length sending unit 12 is the voltage equivalent of the logarithmic value of the value to which the con- trol member CMp, has set the focal length parameter plus the shifted value of the potentiometer assembly P.. This allows the output 0p _L to be appropriately adjusted so that the focal length voltage curve can be ' matched to any point on the object distance voltage curve.

A better understanding of the significance of the shifted value of the potentiometer assembly P. can be had by considering a series of postiions to which it is set. Suppose the object distance control member CM _0D is set as seen in Fig. 1 so that the cam follower roller 24 has been shifted the distance da from the base reference plane AP _Ω1 -. to generate voltage output V in Fig. 3. Now, if the potentiometer assembly P„ is set at the desired value, the motor drive unit MDU will shift the focal length control member CMp, until the cam follower roller 34 is shifted the distance d, from the base reference plane AP _p , as seen in Fig. 1 to generate voltage output , in Fig. 3. It will be noted that at this postition, the voltage V is equal to voltage V, as indicated by the phantom line in Fig.

3 labelled Po.... This takes into account the situation in which the potentiometer assembly P _A is set at the desired ratio.

If one wants the ratio to be such that, the vol- tage output V, ' on the focal length voltage curve is to correspond to the voltage V. on the object distance voltage curve, the potentiometer assembly P is shifted using the knob 15 until the voltage value V _ς is added to the voltage value V, ' so that the apparent voltage in the output O _p , of the sending unit 12 would be the

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value V, illustrated by the shifted dashed line curve in Fig. 3. The value V _g added will be different de¬ pending on which points of correspondence on the focal length voltage curve onewants to correspond to the vol¬ tage V on the object distance voltage curve.

Suppose the potentiometer assembly P. is set so that the focal length voltage curve is defined by the solid line curve in Fig. 2. Now, if the potentiomete-r assembly P. remains in the same position, and the ob¬ ject distance control member CM _oπ is rotated to a new position so that its associated sending unit 11 gene¬ rates a voltage output M as seen in Fig. 3, then the ratio base control unit 14 will cause the motor drive unit MDU to rotate the focal length control member CM _p , so that the voltage output from its associated sending unit 12 will be changed to voltage V, where the volt¬ ages V and V, are again equal. This is illustrated by the phantom line seen in Fig. 3 which is labelled

V F •rcm the foregoing, it will be seen that the appa¬ rent voltage ^' in the output Op, is the sum of the vol¬ tage attributable directly to the potentiometer Pp, plus the voltage attributable to the potentiometer as¬ sembly P.. ^• This means that the equation voltage Pp, + voltage P. = voltage P _QD is satisfied. It follows that, based on the above set forth relationships, this equation can be rewritten as actual focal length ^{κ lo} Sχ smallest focal length ^{+ K} V ⁼

_{Y 1} actual object distance °^x smallest object distance which can be rewritten as _i n actual object distance ^x smallest object distance r ι actual focal length «. *" ^g x smallest focal length ^" V"

It will be noted that, as long as the potentiometer assembl P. remains at any one setting, the value K _v also remains constant. Since K, x, smallest object distance, smallest focal length-, are all constants, it follows' that log [actual object distance/actual focal length] also remains constant as long as the setting of the potentiometer assembly P. remains con¬ stant which implies that actual object distance ₊ . actual focal length ^{= onstant} -

Thus, once the potentiometer assembly P. is set, the ratio of ob ect distance to focal length is maintained constant which is the characteristic desired. It will further be understood that changing the potentiometer assembly P. to another constant will still cause the ratio to remain constant but to a constant of a diffe¬ rent value. This is also a desired characteristic.

It will be further appreciated that the lens L _pz has two degrees of freedom. The interlock mecha- nism 10 allows the two control parameters to be inter¬ connected so that the number of degrees of freedom are reduced to one. This greatly simplifies the operation of the lens L _p „ so as to keep the image size constant while the distance between the subject being photo- graphed and the lens changes. Recently, cameras with automatic focusing have been developed. The mechanism 10 can be easily added to these automatic focusing cameras when they are equipped with a zoom lens so that, with the automatic focusing feature, the number of degrees of freedom of the lens system is reduced to zero. Because the power of the electric motor M _p , required to operate the control member CM _p , is rela¬ tively low, the control member CM _p , can be manually shifted momentarily by overpowering the motor Mp, if it is desirable to momentarily change the focal length

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parameter. When the control member CMp, is released, the motor Mp, will power the control member CMp, back to its prescribed ratio position for continued opera¬ tion.

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Vb. Second Embodiment

Fig. 4 illustrates a second embodiment that me¬ chanically maintains the desired ratio between focal length and object distance and is applied to a zoom 5 lens L- for a still camera B^. Lens L~ has an object distance control member CM _QD and focal length control member CM _p , mounted on lens body B, about lens axis

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Interlock mechanism 110 connects members CM _on

10 and CM _p , to maintain the desired image size. Mecha¬ nism 110 has an object distance control cam 111 car¬ ried by the control member CM _0Ω and a focal length control cam 112 carried by control member CMp, . Cam

111 has a camming slot 121 whose logarithmic rela-

15 tionship with control member CM ₀ corresponds to that of camming surface 26 for the first embodiment. Cam

112 has a camming slot 125 whose logarithmic rela¬ tionship with control member CM _p , corresponds to that of camming surface 36 for the first embodiment.

20 An interconnect unit 14 selectively connects the cams 111 and 112 to maintain desired ratios between the control members CM _QD and CMp, . Housing 130 of unit 114 is mounted on lens body B, and slidably mounts cam follower members 131 and 132 for movement

25 along a path R, parallel to lens axis A, . The cam followers 131 and 132 can slide in housing 130 inde¬ pendently of each other but can also be locked to¬ gether using the teeth 144 and 145 on members 131 and 132 and clamp 148 so that the -members 131 and 132

30 move as a unit. It will be noted that the members 131 and 132 can be locked together at any position relative to each other over their respective ranges of movement. The member 131 is drivingly connected to the object distance camming slot 121 through

35 follower 136 while member 132 is drivingly connected

to the focal length camming slot 125 through follower 140. Thus, rotation of control member CM _0D axially displaces cam follower member 131 and axial movement of member 131 rotates member CM _QD through slot 121 while rotation of control member CMp, axially dis¬ places cam follower member 132 and axial movement of member 132 rotates member CMp, through slot 125. When the cam follower members 131 and 132 are locked togeτ ther, it will be seen that rotation of one of the con¬ trol members CM _QD or CMp, causes ^' an appropriate rota- tion of the other control member CM, O,,D, or CM-F-,L to main- tain a constant ratio between object distance and focal length.

Because the slots 121 and 126 are logarithmic, it will be seen that the displacement da of the cam fol- lower member 131 from the base object distance plane AP _0D over its range d,, corresponds to that of the first embodiment and that the displacement d, of the ^' cam follower member 132 from the base focal length plane AP _p , over its range d ₂ corresponds to that of the first embodiment. It will be noted that the planes AP^ _n and AP _p , are spaced apart a fixed distance d,. When the cam follower members 131 and 132 are selec¬ tively locked together to selectively fix the distance d between the followers 136 and 140 at a constant value, it will be seen that d3, - da„ + -d,b = constant ( -d„ c) ^J .

Because of the logarithmic nature of d and d, , this equation can be rewritten as „ , smallest object distance ^s x smallest focal length _v - . actual object distance „„„,.„.„„_ _{► A}

^{K l0} Sχ actual- focal- length ⁼ constant -d ₃ .

Since K, x, smallest object distance, smallest focal length, and d, are all constants, it follows that log

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[actual object distance/actual focal length] is also constant which implies that

—act—uala—o ^■ ___—bj—ec ^~ —tTdis _tance ⁼ const.a . actual focal length nt. Thus, once the members 131 and 132 are locked together, the ratio of object distance to focal length is main¬ tained constant so that rotation of the control mem¬ bers CM _nD or CM _p , also drives the other control mem¬ ber CM - _j , or CMp, to keep the ima.ge size constant. Any desired ratio can be maintained between object dis¬ tance and focal length simply by initially setting the control members at the desired ratio before the cam follower members 131 and 132 are locked together.

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Vc. Other Embodiments

While the first two embodiments of the invention are incorporated in control systems having only two degrees of freedom, the invention can be applied ^' to any control system having any number of degrees of freedom. In any such system, each of those ^' control parameters which are sought to be controlled would have sending means for generating an output which is logarithmic of the particular values over the operating parameter ' range and interlock means for selectively controlling the various control parameters so that selected fixed differences can be maintained between the logarithmic outputs of the sending means.

Figs. 5 and 6 illustrate a control system which has three independent control parameters and thus three degrees of freedom. The control system has its three control parameters controlled by three different con¬ trol members CM, -CM- where each can be manually ad- justed. ith control knobs CK..-CK, and/or electrically adjusted with motors M-.-M,. The control members CM,- CM, are illustrated as axially movable along respec¬ tive paths P.-P-.

The interlock mechanism 210 has a separate sending unit 211 connected to each control member CM,-CM, re¬ spectively referenced 211,-211-. The sending units may be mechanical or electromechanical but are illus¬ trated as electrical by way of example. Sending units 211,-211- generate respective outputs 0,-0, that cor¬ respond to the logarithm of the operating parameter value associated with the particular sending unit as set by the control members CM..-CM-.

As seen in Fig. 6, the output 0, is connected to ratio base control units 214. and 214 ', to comparators 215. and 215 _β ; and to selector switch 218.,-218-g and 218 . Output 0 ₂ is connected to ratio base control

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units 214. and 215 _c ; to comparators 215. and 215 _c ; and to selector switches 218A, 218B and 218C. Output 0 ₃ is connected to ratio base control units 214^ and 2145,'; to comparators 215-n and 215 _c ; and to selector switches as 218. , 218-g and 218^. The ratio base control units 214 are activated by actuating switches SW which may ^¬ be ganged to operate together. Closure of switches SW causes the ratio base control unit 214. to generate output OΛ to the comparator 215. representative of the difference between outputs 0, and 0~ at the time of closure of switch SW, causes the ratio base con¬ trol unit 214 _β to generate output 0 _β to the comparator 215,, representative of the difference between outputs 0, and 0, at the time of closure of switch SW, and causes the ratio base control unit 214.-, to generate output O to the comparator 215p representative of the difference between outputs 0 ₂ and 0, at the time of closure of switch SW.

Output 0. biases the comparator 215. to generate a compared control output signal S. to selector switch 218. until the difference between outputs 0, and 0 ₂ matches that indicated by the ratio base control unit 214.. Output O- _o biases the comparator 15^ to gene¬ rate a compared control output signal S _β to selector switch 218-n until the difference between outputs 0, and 0, matches that indicated by the ratio base con¬ trol unit 214 _B • Output O biases the comparator 215,-, to generate a compared control output signal S„ to selector switch 218 until the difference between outputs 0- and 0- matches that indicated by the ratio base contiol unit 214,,. Switch 218. selectively con¬ trols motors M, and M ₂ , switch 218,, selectively con- trols motors M, and MM,, aanndd sswwiittcch 218 controls motors M ₂ and M, . The motors M, -M, can be manually individually controlled through switches OS, -OS-,

The operator initially sets the value of the ope¬ rating parameters to the desired ratios and closes the activation switches SW to energize ratio base control units 214»-214 _c and activate the interlock mechanism 5 210. Now if the setting on one αf the control members is changed, the mechanism 210 will appropriately move the other control members to maintain the set ratio between the operating parameters. For example, - assume control member CM_. is moved to change its ope¬

10. rating parameter and change output 0, . The compara¬ tor 215. senses a differential between outputs 0, and 0- different from that set in ratio base control unit 214. and operates motor M- through switch 218. to shift member CM- until the differential sensed

15 by comparator 215. again matches that initially set in ratio base control unit 214.. At the same time, the comparator 215-n senses a differential between out¬ puts 0, and 0- different from that set in ratio base control unit 214 _β and operates motor M, through switch

30 218 _β to shift member CM, until the differential sensed by comparator 215 _β again matches that initially set in ratio base control unit 214g. Thus, it will be seen that the control members CM- and CM- have been moved until the operating values controlled

25 thereby have the same ratio as they had initially. It will also be noted that the first changed output 0,- 0, appropriately enables only those selector switches 218.-218^ to cause the other motors M, -M- not associa- ted with the first changed output 0, -0- to be con¬

30 trolled from the comparators 215.-215,,. The mechanism 210 may be used to interlock any two of the control members as well as all three as explained above.

It will be noted that the interlocking process need not be a one step procedure, but may be performed 35 in separate steps. For example, a control system with

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eight independent operating parameters V, -V _g would have eight degrees of freedom. One may interlock parameters V ₂ , _{ς >} and V ₇ ; interlock parameters V,, V-, and Vg; and interlock parameters V. and Vg i ^' n accordance with the invention. The system would then have .three degrees of freedom with the ratios V ₂ / , V ₂ / ₇ or V-/V- being constant, the ratios V,/V-, V,/Vg or V^/V, being constant and the ratio V./V ₆ being constant. The ratio. of the parameters in any one interlocked group to the ratio of the parameters in any other interlocked group may be independently changed as desired. At some later time, any of the three interlocked groups of para¬ meters may be interlocked with any other interlocked group of parameters in accordance with the invention to reduce the system degrees of freedom to two, or all of the interlocked groups of parameters may be interlocked in accordance with the invention to re¬ duce the system degrees of freedom to one.