Patent Description:
Precision motion systems, in particular semiconductor processing equipment such as positioning devices, coordinate measuring machines or robots, comprise active anti-vibration systems, as disclosed in <CIT> or <CIT>,
for isolating precision motion systems from ground vibrations. Active anti-vibration systems typically comprise several active bearings which are assembled between a granite base onto which the precision motion system can be mounted and a metallic frame that rests on the floor. Active anti-vibration systems therefore ensure the operation of precision motion systems with as little parasitic movement as possible, as a result of which a high positioning or measurement accuracy is obtained.

Each active bearing comprises linear motors, vertical and horizontal sensors that are connected to electronic controllers to drive each linear motor as a function of the output of vertical and horizontal sensors and as a function of the known movements of the precision motion system to avoid unwanted movements of the granite base and dampen any residual movements. The active bearings support the granite base upwardly using a mechanical spring or an air spring, thereby passively isolating the base from the floor vibrations.

Active bearings are therefore complex systems that sometimes must be replaced in case of failure. Replacement of any active bearing is however difficult as it implies disassembling the granite base from the metallic frame in order to unscrew the active bearings.

An aim of the present invention is therefore to provide an active anti-vibration system for a precision motion system, adapted for easy replacement of active bearings in case of failure.

Another aim of the present invention is to provide a method for disassembling an active bearing from the active anti-vibration system for easy replacement of the active bearing.

These aims are achieved notably by an active anti-vibration system according to claim <NUM>.

According to claim <NUM>, each of the first set of fixation elements is in the form of a screw. The upper panel comprises threaded through-holes axially aligned with respective through-holes of the mounting base and receiving a threaded part of respective screws.

In an embodiment, each through-hole of the mounting base comprises an upper portion having a first diameter and a lower portion having a second diameter smaller than the first diameter to form a shoulder onto which the screw head of a corresponding screw rests to secure the active bearing upper panel to the lower side of the mounting base.

According to claim <NUM>, each of said second set of fixation elements is in the form of a screw. The lower panel of each active bearing comprises trough-holes and captive screw retainers. Each captive screw retainer comprises a housing lodging a screw engaged with respective through-hole of the lower panel of the active bearing. The housing comprises an upper portion having a central opening axially aligned with the screw head of the screw. The upper side of the supporting frame comprises threaded holes receiving a threaded part of the screw of respective captive screw retainer.

In an embodiment, the trough-holes of each active bearing lower panel are axially aligned with respective threaded through-holes of each active bearing upper panel.

In an embodiment, each captive screw retainer further comprises a magnet arranged to hold the screw when said screw is removed from the corresponding threaded hole of the upper side of the supporting frame during the disassembly of the corresponding active bearing for its replacement.

Another aspect of the invention relates to a method for disassembling and removing an active bearing from the active bearing compartment of the active anti-vibration system as described above. The method comprises the steps of:.

The invention will be better understood with the aid of the description of several embodiments given by way of examples and illustrated by the figures, in which:.

With reference to <FIG>, the active anti-vibration system <NUM> comprises a mounting base <NUM> having an upper side 12a onto which a precision motion system, for example a semiconductor processing equipment, can be mounted. The mounting base <NUM> is preferably in granite and comprises multiple threaded holes for fixing different type of precision motion systems. The mounting base <NUM> may further comprise a support <NUM> for installing an optical imaging device, such as a microscope for visual inspection. The active anti-vibration system <NUM> further comprises a supporting frame <NUM> resting on the floor, and active bearings <NUM> mounted into an active bearing compartment <NUM> between the mounting base <NUM> and the supporting frame <NUM>. Each active bearing <NUM> comprises a mechanical spring or an air spring (not shown) to support the mounting base, and passively isolate the base from the floor vibrations.

Four active bearings <NUM> are typically mounted on the four corners of the active bearing compartment <NUM> which is defined by a lower side 12b of the mounting base <NUM> and an upper side <NUM> of the supporting frame <NUM> as shown for example in <FIG>. The active bearing <NUM> comprises inertial sensors and actuators to provide together a six degrees-of-freedom (DOF) measurement of the motions of the mounting base <NUM> as well as six-DOF actuation devices. Six-DOF measurement is obtained with six or more inertial sensors shared out among the active bearings. Six-DOF actuation can be realized with six or more actuators shared out among the active bearings. In a preferred embodiment, three active bearings comprise each a horizontal and a vertical actuator, and a horizontal and a vertical inertial sensor, and the fourth active bearing comprises a horizontal and a vertical actuator only.

The sensors and actuators are built into an active damping multiple-inputs/multiple-outputs (MIMO) control loop that dampens any residual vibrations of the granite base. An active feedforward path is implemented which uses the known motions of the motion system to compute forces and torques to be applied by the actuators to the mounting base to compensate for reaction forces and thus avoid unwanted motions of the base.

Each active bearing <NUM> further comprises an upper panel <NUM> mounted against the lower side 12b of the mounting base <NUM>, and a lower panel <NUM> mounted against the upper side <NUM> of the supporting frame <NUM>.

With reference to <FIG>, the mounting base <NUM> of the active anti-vibration system <NUM> comprises through-holes <NUM> extending from the upper side 12a to the lower side 12b of the mounting base <NUM>. Each through-hole <NUM> of the mounting base <NUM> comprises an upper portion having a first diameter d1 and a lower portion having a second diameter d2 smaller than the first diameter d1 to form a shoulder <NUM>. A first set of fixation elements <NUM> are arranged into the through-holes <NUM> to fix the upper panel <NUM> of each active bearing <NUM> against the lower side 12b of the mounting base <NUM>. The fixation elements <NUM> are preferably screws <NUM> comprising a screw head 15a resting on the shoulder <NUM> and a threaded part 15b extending through the lower portion of the second diameter d2, wherein a distal portion of the threaded part 15b is screwed into a corresponding threaded through-hole <NUM> of the upper panel <NUM> of the active bearing <NUM>.

A second set of fixation elements are arranged into through-holes <NUM> of the lower panel <NUM> of each active bearing <NUM> to fix the active bearing lower panel <NUM> to the upper side <NUM> of the supporting frame <NUM>. In an advantageous embodiment, the second set of fixation elements are in the form of three or more captive screw retainers <NUM>.

With reference to <FIG>, each captive screw retainer <NUM> comprises a housing <NUM> which may be obtained for example by an additive manufacturing process. The housing is typically in plastic and is adapted to house a screw <NUM> engaged with respective through-hole <NUM> of the active bearing lower panel <NUM>. The housing <NUM> comprises an upper portion <NUM> having a funnel shape with a central opening <NUM> aligned with the screw head 48a of the screw <NUM> as shown in <FIG>. The upper side <NUM> of the supporting frame <NUM> comprises threaded holes <NUM> into which are screwed a threaded part 48b of the screw <NUM> of respective captive screw retainer <NUM>.

Each captive screw retainer <NUM> further comprises a magnet <NUM> arranged in the housing <NUM> to hold the screw <NUM> within the captive screw retainer when the screw is removed from the corresponding threaded hole <NUM> of the upper side <NUM> of the supporting frame <NUM> during the disassembly of the corresponding active bearing <NUM> for its replacement.

The housing <NUM> of the captive screw retainer <NUM> may be fixed to the active bearing lower panel <NUM> with different fixation means. In the illustrated embodiment, the housing <NUM> is screwed onto the active bearing lower panel <NUM>. In this respect, the housing <NUM> comprises two lateral openings <NUM> comprising each a through-hole <NUM> extending through the mounting base of the housing for accommodating a screw <NUM> ensuring the connection with the active bearing lower panel <NUM> as shown in <FIG>. In a non-illustrated embodiment, the housing of the captive screw retainers may simply be glued onto the active bearing lower panel.

In case the captive screw retainers <NUM> need to be placed very near the edge of the upper side surface of the supporting frame <NUM> or mechanical parts in the active bearing limit the space available, the housing <NUM> can be cut along a vertical plane to have flat side <NUM> as shown for example in <FIG>.

The trough-holes <NUM> of the active bearing lower panel <NUM> are axially aligned with respective threaded through-holes <NUM> of active bearing upper panel <NUM> for easy replacement of any active bearing in case of failure as described subsequently.

Referring to <FIG> and <FIG>, which show an operation to remove a faulty active bearing <NUM> from the active anti-vibration system for its replacement, a screwing tool is used to remove the first set of screws <NUM> connecting the active bearing upper panel <NUM> to the lower side 12a of the mounting base <NUM>. For this operation a screwdriver or a torque wrench <NUM>, such as a ratchet wrench <NUM>, may be used. In the latter case, a rod 102a with a distal end configured to engage the screw head 15a of the screws <NUM> is used together with the wrench <NUM> for unscrewing the threaded part 15b of the screws from respective threaded through-hole <NUM> of the active bearing upper panel <NUM>. The distal end of the rod 102a is magnetized to lift the screws <NUM> out of the trough-holes <NUM> of the mounting base <NUM>.

Once the screws <NUM> are removed from the mounting base <NUM>, the wrench <NUM> is used with another rod 102b which is specifically designed to unscrew the screw head 48a of respective captive screw retainer <NUM> of the active bearing lower panel <NUM> from the upper side 12a of the mounting base <NUM>. The length of this rod 102b is therefore significantly longer than the rod 102a used for removing the first set of screws <NUM>. The outer diameter of this rod 102b is also smaller than both the lower portion d2 of the trough-holes <NUM> and the threaded through-hole <NUM> of the active bearing upper panel <NUM>.

The wrench <NUM> can thus be handled to introduce the rod 102b into each through-hole <NUM> and to move its distal end downwardly though the corresponding threaded through-hole <NUM> of the active bearing upper panel <NUM> down to respective captive screw retainer <NUM>. The funnel-shaped upper portion <NUM> of the housing <NUM> of respective screw retainer <NUM> guides the distal end of the rod 102b into the central opening <NUM> such that the distal end of the rod 102b engages with the screw head 48a of respective captive screw retainer <NUM>.

The wrench <NUM> is then handled for unscrewing the threaded part 48b of the screws from respective threaded hole <NUM> of upper side <NUM> of the supporting frame <NUM> of the anti-vibration system <NUM>. As soon as the threaded part 48b of these screws are disengaged from the supporting frame upper side and the rod 102b is disengaged from the screw head 48a, the magnet <NUM> of the captive screw retainer <NUM> attracts and hold the screws <NUM> such that the end of the threaded part 48b is inside respective through-hole <NUM> of the active baring lower panel <NUM> and distant from the upper side <NUM> as shown in <FIG>. When all captive screws <NUM> have been released, the active bearing <NUM> can thus be slid along the upper side <NUM> out of the active bearing compartment <NUM> without scrapping the upper side surface of the supporting frame <NUM>. A screw jack <NUM> can be used to temporarily slightly increase the height of the active bearing compartment <NUM> to facilitate the sliding of the active bearing <NUM> out of the active bearing compartment and into said compartment.

Before mounting a new active bearing <NUM>, the magnet <NUM> of each captive screw retainers <NUM> mounted on the active bearing lower panel <NUM> hold respective screws in the same position shown in <FIG>. The new active bearing <NUM> can thus be placed inside the active bearing compartment <NUM> of the anti-vibration system <NUM> and slid on the upper side surface of the supporting frame in its mounting position, whereby the threaded through-holes <NUM> of the active bearing upper panel <NUM> and the through-hole <NUM> of the active bearing lower panel <NUM> are axially aligned with the respective through-holes <NUM> extending from the upper side 12a to the lower side 12b of the mounting base.

With reference to <FIG>, the ratchet wrench <NUM> is then handled in a similar way as for disengaging the screws from respective threaded hole <NUM> of upper side <NUM> of the supporting frame <NUM> of the anti-vibration system as explained above. This time, the ratchet wrench <NUM> is handled to fix the active bearing lower panel against the supporting frame by screwing the threaded part of screws in the respective threaded holes <NUM> of the upper side of the supporting frame as shown in <FIG>.

Claim 1:
Active anti-vibration system (<NUM>) comprising a mounting base (<NUM>) having an upper side (12a) onto which a motion system can be mounted, a supporting frame (<NUM>) resting on the floor, and active bearings (<NUM>) mounted into an active bearing compartment (<NUM>) defined by a lower side (12b) of the mounting base (<NUM>) and an upper side (<NUM>) of the supporting frame (<NUM>), each active bearing (<NUM>) comprising actuators for imparting counteracting forces to the mounting base (<NUM>) to compensate for reactions forces generated by the motion system, when mounted onto the mounting base (<NUM>) and operating, to avoid unwanted movements of the mounting base (<NUM>) and dampen any residual movements, each active bearing (<NUM>) further comprising an upper panel (<NUM>) mounted against the lower side (12a) of the mounting base (<NUM>) and comprising threaded through-holes (<NUM>), a lower panel (<NUM>) mounted against the upper side (<NUM>) of the supporting frame (<NUM>), and a first set of screws (<NUM>) securing the active bearing lower panel (<NUM>) to the upper side (<NUM>) of the supporting frame (<NUM>), wherein
the mounting base (<NUM>) comprises through-holes (<NUM>) extending from the upper side (12a) to the lower side (12b) of the mounting base (<NUM>) and axially aligned with the through-holes (<NUM>) of the upper panel (<NUM>) of respective bearing member (<NUM>), and a second set of screws (<NUM>) comprising a threaded part (15b) screwed into respective through-holes (<NUM>) to secure the active bearing upper panel (<NUM>) to the lower side (12b) of the mounting base (<NUM>) and characterized in that the lower panel (<NUM>) of each active bearing (<NUM>) comprises trough-holes (<NUM>) and captive screw retainers (<NUM>), each captive screw retainer comprising a housing (<NUM>) lodging a screw (<NUM>) of said first set of screws, said screw being engaged with respective through-hole (<NUM>) of the lower panel (<NUM>) of the active bearing, the housing (<NUM>) comprising an upper portion (<NUM>) having a central opening (<NUM>) axially aligned with the screw head (48a) of the screw (<NUM>), the upper side (<NUM>) of the supporting frame (<NUM>) comprising threaded holes (<NUM>) receiving a threaded part (48b) of the screw (<NUM>) of respective captive screw retainer (<NUM>).