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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/327,154, filed Apr. 23, 2010, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to an electric circuit with speed control and diode separation for use with an electrically actuatable mechanism. In one embodiment, the electrically actuatable mechanism is an electro-hydraulic actuator of a door assist system. 
     BACKGROUND OF THE INVENTION 
     It is known to use an electrically actuatable mechanism to move a heavy object, such as a heavy door. One such mechanism is an electro-hydraulic actuator. 
       FIG. 1  is a schematic illustration of a conventional electro-hydraulic actuator  10 . The electro-hydraulic actuator  10  includes an electric motor  12  that is operatively coupled to a hydraulic pump  14 . The electric motor  12  is operable for driving the hydraulic pump  14  in opposite first and second rotational directions. The hydraulic pump  14  draws fluid from a reservoir  16  and provides the fluid to an actuator  18 . The actuator  18  includes a piston  24  that is movably mounted within a cylinder bore  26 . The piston  24  divides the cylinder bore  26  into first and second chambers  28  and  30 , respectively. The first chamber  28  may be referred to as a piston (or head) side chamber and, the second chamber  30  may be referred to as a rod side chamber. A rod  32  of the actuator  18  which is affixed to or integral to the piston  24  extends through the second chamber  30  and outwardly of a housing (not shown) of the electro-hydraulic actuator  10 . Commonly, the electric motor  12 , the hydraulic pump  14 , the reservoir  16  and the actuator  18  are integrated into a single, compact package. 
     The electro-hydraulic actuator  10  is operable for extending or retracting the rod  32  for causing relative movement of two structures, one attached to the housing of the package and the other attached to the end of the rod. For example, in a door assist system associated with a vehicle, extending and retracting the rod  32  moves the door relative to the vehicle body. To extend the rod  32  of the electro-hydraulic actuator  10 , the electric motor  12  is operated to drive the hydraulic pump  14  in a first rotational direction causing hydraulic fluid drawn from the reservoir  16  and chamber  30  to be directed into the first chamber  28  of the actuator  18 . The fluid directed into the first chamber  28  creates a pressure differential between the first and second chambers  28  and  30  of the actuator  18  that moves the piston  24  to increase the volume of the first chamber  28  and decrease the volume of the second chamber  30 , thus extending the rod  32 . To retract the rod  32 , the electric motor  12  is operated to drive the hydraulic pump  14  in a second rotational direction, opposite the first rotational direction, causing hydraulic fluid drawn from the chamber  28  to be directed into the second chamber  30  of the actuator  18 . The fluid directed into the second chamber  30  creates a pressure differential in which the pressure in the second chamber is higher than that in the first chamber  28 . As a result of the differential pressure, the piston  24  moves to increase the volume of the second chamber  30  and decrease the volume of the first chamber  28 , thus retracting the rod  32 . 
     SUMMARY 
     At least one embodiment of the invention provides an electric circuit for actuating an electrically actuatable mechanism comprising: a controller, an operator input that when actuated provides a signal to the controller; a relay adapted to provide a voltage to the electrically actuatable mechanism in response to a signal from the controller, the relay adapted to vary the voltage in response to the signal, wherein the controller is adapted to provide the relay with signals for varying the voltage. 
     At least one embodiment of the invention provides an electric circuit for actuating an electrically actuatable mechanism comprising: a controller; multiple operator inputs each of which, when actuated, provides a signal to the controller; a relay adapted to provide a voltage to the electrically actuatable mechanism in response to a signal from the controller, wherein the relay also operates to control the signal to the controller in response to actuation of one of the operator inputs, a diode associated with each operator input and the electrically actuatable mechanism preventing a back-feeding of the voltage from the relay. 
     At least one embodiment of the invention provides an electro-hydraulic actuator system comprising: an actuator cylinder; an electric motor operatively coupled to a hydraulic pump; a reservoir of hydraulic fluid; and an electric circuit for actuating the actuator cylinder, the circuit comprising a controller, an operator input that when actuated provides a signal to the controller, a relay adapted to provide a voltage to the electrically actuatable mechanism in response to a signal from the controller, the relay adapted to vary the voltage in response to the signal, wherein the controller is adapted to provide the relay with signals for varying the voltage. 
     At least one embodiment of the invention provides a method of operating an electro-hydraulic actuator system comprising an actuator cylinder, an electric motor operatively coupled to a hydraulic pump, a reservoir of hydraulic fluid, and an electric circuit including a controller for actuating the actuator cylinder, comprising the steps of: providing an operator input that when actuated provides a signal to the controller, providing a voltage through a relay to the actuator in response to the signal from the controller, varying the voltage in response to the signal, wherein the controller is adapted to provide the relay with signals for varying the voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this invention will now be described in further detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a prior art electro-hydraulic actuator; 
         FIG. 2  is a schematic view of a prior art electrical circuit of the type associated with the actuator of  FIG. 1 ; 
         FIG. 3  is a schematic view of an embodiment of an electric circuit of the present invention utilizable with the actuator of  FIG. 1 ; 
         FIG. 4  is a schematic view of a prior art electrical power activation circuit of the type associated with the actuator of  FIG. 1 ; and 
         FIG. 5  is a schematic view of an embodiment of an electric power activation circuit of the present invention utilizable with the actuator of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention relates to electrical circuit designs that may be incorporated into the electrical circuit for actuating a mechanism such as, for example, an electro-hydraulic actuator used in a door assist system. The fundamental operation of a door assist system is to open and/or dose a door when the proper input is provided. Commonly, the proper input is provided by an operator actuating an open/close rocker switch. 
     As shown in  FIG. 2 , in a conventional electrical circuit used in, for example, a door assist system, an input is given to a controller  62  via the closing of the rocker switch  64  by the operator. By closing the rocker switch  64 , a signal is applied to the controller  62  and, in response to the signal, the controller  62  applies an output voltage to a relay  66  allowing power to flow from a battery  68  to the electrically actuatable mechanism  70 . 
     The challenge with this conventional design is that as soon as the relay is closed, full voltage is applied to the electrically actuatable mechanism  70  and the load (such as the door) immediately begins moving. This may give the operator the appearance that the load is running away, and can also impart a “bouncing” of the load due the sudden movement of the mechanism, particularly when the mechanism imparts an impact force against the load. To address this issue, the electrical circuit of the present invention includes speed control capabilities. 
       FIG. 3  illustrates an electrical circuit constructed in accordance with a first embodiment of the present invention and including the speed control capabilities. In the electrical circuit of  FIG. 3 , the controller  80  is responsive to the operator closing the rocker switch  82  for providing a Pulse-width Modulated (PWM) output signal to a MOSFET relay  84 . The controller  80  is operable to gradually start and stop the actuation of the mechanism  70  (such as the electro-hydraulic actuator  10 ) by ramping the voltage provided to the mechanism through control of the PWM signal. Another added function is the ability to have complete speed control of the mechanism  70  as a function of the PWM signal applied. As the PWM output signal provided by the controller  80  may be easily modified, the user has the ability to modify the speed control as desired. An added benefit of the electric circuit of  FIG. 3  is that it utilizes only one MOSFET relay and thus, is simple and robust. 
     In order to save power, it is desirable for a door assist system, for example, to shut down a predetermined time after being actuated. When the system is shut down, or idle, it is expected that it will become active almost immediately upon an input by the operator (e.g., closing of the rocker switch  90 ). To accomplish this power savings, in a conventional system, the voltage signal applied by the user input is used to close an associated relay  92  or  94  with this relay thereafter applying a voltage to the controller  62  for activating the controller. An exemplary circuit showing this design is provided in  FIG. 4 . When activated, the controller  62  will keep the relay closed for the required time by applying voltage to the relay through an output. 
     Many systems, such as a door assist system, has multiple user inputs for activating the system. When multiple user inputs are used, the electric circuit can get very complex with a need for a dedicated relay for each of the user inputs and each voltage output, as illustrated in  FIG. 4 . The reason for having separate inputs is to avoid the risk of back-feeding voltage into one of the other inputs or the output of the controller. 
     To address this issue with fewer components, the electric circuit of the present invention, as shown in  FIG. 5 , incorporates diodes  102  in each of the lines leading to the relay  104 . This allows all three signal lines to pass through the same relay, thus reducing components, space and complexity of the system. 
     Although the principles, embodiments and operation of the present invention have been described in detail herein, this is not to be construed as being limited to the particular illustrative forms disclosed. They will thus become apparent to those skilled in the art that various modifications of the embodiments herein can be made without departing from the spirit or scope of the invention.

Summary:
An electric circuit with speed control and diode separation for use with an electrically actuatable mechanism. An operator input provides a signal to a controller of the electric circuit. The controller causes a MOSFET relay to provide a voltage to the electrically actuatable mechanism. The relay is adapted to vary the voltage in response to pulse width modified signals from the controller.