Work holders – With fluid means – Cylinder-piston means in series with additional positioning...
Reexamination Certificate
1998-08-26
2001-03-13
Watson, Robert C. (Department: 3723)
Work holders
With fluid means
Cylinder-piston means in series with additional positioning...
C269S233000, C269S235000
Reexamination Certificate
active
06199846
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electric power operated clamp for moving at least one clamp arm between a clamped position and a released position, and in particular, an adjustable mechanism that converts the rotary motion of an electric power source into linear reciprocal movement of a drive member and then into rotary motion of the clamp arm.
BACKGROUND OF THE INVENTION
Various clamping devices have been provided for immovably securing a workpiece or workpieces with respect to a stationary support during a machining and/or welding operation. Most of these devices have incorporated fluid operated actuators, such as hydraulic or pneumatic operated piston and cylinder actuators. While these devices are satisfactory for clamping workpieces to a stationary support, difficulties arise in using clamps of this configuration for use in non-stationary support situations, such as moving transfer devices, conveyors, shuttles or the like. In addition, the use of hydraulic fluid in non-stationary applications can be the source of hydraulic fluid leaks, while the use of pneumatic actuators increases cost of operation by requiring the production of sufficient quantities of compressed air of predefined quality for operating clamping devices. Compressed air generally requires the use of fixed or flexible conduits to communicate the compressed air with the actuator, and may produce compressed air leaks increasing operating costs. Furthermore, it is difficult to obtain a harmonic motion clamp action with a hydraulic or pneumatic actuator, sometimes referred to as a “soft-touch” clamp, where the clamp decelerates adjacent the clamped and/or released position thereby eliminating the need for “bumpers” or other shock absorbing elements. Typically, hydraulic and pneumatic actuated clamps require complex control mechanisms to adjust the rate of actuation of the clamp to eliminate or reduce the amount of shock absorbed as the clamp reaches the clamped position and/or the released position.
SUMMARY OF THE INVENTION
It is desirable in the present invention to provide an electric power operated clamp to eliminate the recognized deficiencies in hydraulic and/or pneumatic operated clamps. In addition, it is desirable in the present invention to provide an electric power operated clamp having harmonic clamp motion, where the clamp decelerates as it approaches the clamped position and/or released position. The present invention provides a power operated clamp including an electric motor means for imparting a rotary motion driving force. A drive member is operably associated with the electric motor means. First converting means connects the drive member to the electric motor means. The first converting means converts the rotary motion driving force of the electric motor means into a linear reciprocal motion of the drive member. A clamp member is operably associated with the drive member. Second converting means connects the clamp member to the drive member. The second converting means converts the linear reciprocal motion of the drive member into rotary motion of the clamp arm to move the clamp member between a clamped position and a released position.
In the first configuration, the first converting means includes an elongate arm connected to a shaft of the electric motor means which extends radially outward for rotation with the shaft. A cam follower is connected to the elongate arm spaced radially from the shaft. The drive member is mounted for linear reciprocal movement along a fixed path. The drive member has a cam surface defining a slot adjacent one longitudinal end of the elongate drive member. The slot extends generally normal to the fixed path of the drive member. The cam follower operably engages within the slot for converting the rotational movement of the cam follower into linear movement of the drive member.
In an alternative configuration, the first converting means can include an eccentric member connected to the electric motor means for rotation therewith and having an external periphery. The drive member can include a connecting rod and slide block. The connecting rod has a complementary aperture formed therein for operably receiving the external periphery of the eccentric member. The connecting rod also includes a pivot pin for operably connecting to the slide block, such that the slide block is driven in reciprocal motion by the connecting rod in response to rotation of the eccentric member.
Another alternative embodiment can include the first converting means having a barrel cam connected to the electric motor means for rotation therewith. The barrel cam has a generally helical cam surface formed on an external periphery. The drive member has an aperture for receiving the barrel cam. A cam follower is supported by the drive member and is engageable with the cam surface for driving the drive member in linear motion in response to rotary motion of the barrel cam. Preferably, the generally helical cam surface is formed having reduced longitudinal spacing between turns adjacent one or both longitudinal ends to impart a harmonic motion to the clamp arm while approaching the respective end limit of movement corresponding to the clamped position and the released position.
In the preferred embodiment, the present invention provides an adjustable converting means for converting the rotary motion of the power means into linear reciprocal motion of the drive member. The adjustable converting means includes the first converting means having a crank arm connected to the power means and extending radially outward for rotation about an axis of rotation. The follower is connected to the crank arm and spaced radially from the axis of rotation. The drive member is mounted for reciprocal movement along a fixed path wherein the cam surface of the drive member defines the slot. The follower operably engages the slot to convert the rotational movement of the follower into linear movement of the drive member. The second converting means converts the linear reciprocal motion of the drive member into rotary motion of the clamp member.
A manual adjustment means is also provided in the preferred embodiment for adjusting the stroke of the linear reciprocal motion of the drive member. The manual adjustment means provides the crank arm with a plurality of apertures radially spaced from the axis of rotation wherein the follower is removably inserted in at least one of the apertures of the crank arm. The drive member includes a threaded rod and an outer shaft wherein the outer shaft threadingly receives the rod. The outer shaft and the rod threadingly adjust along the longitudinal axis of the drive member to adjust the length of the drive member in response to the position of the follower in the crank arm.
The preferred embodiment also provides an automatic adjustment means to automatically adjust the length of the drive member in response to the driving force of the power means and the position of the clamp member. The automatic adjustment means provides the drive member with a telescopic portion telescopically moveable along the longitudinal axis of the drive member between an extended position and a contracted position. A positive stop limits the telescopic movement of the telescopic portion between the extended position and the contracted position. At least one compression spring biases the telescopic portion of the drive member toward the extended position.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.
REFERENCES:
patent: 3599957 (1971-08-01), Blatt
patent: 4459945 (1984-07-01), Chatfield
patent: 4494739 (1985-01-01), Valentine
patent: 4723767 (1988-02-01), McPherson et al.
ISI Norgren Inc.
Watson Robert C.
Young & Basile P.C.
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