Actuator system and method for extending a joint

An actuator system for assisting extension of a biological joint is provided with a motor assembly, a rotary-to-linear mechanism, and an extension stop. The rotary-to-linear mechanism includes a screw that accepts rotational output of the motor assembly, and a nut that cooperates with the screw to convert rotational movement of the screw to linear movement of the nut. The extension stop is driven by linear movement of the nut in an extension direction to cause extension of the biological joint. The motor assembly, the rotary-to-linear mechanism and the extension stop cooperate to allow unpowered flexion of the joint. The system is configured without a flexion stop, and is configured such that the nut cannot drive the joint in a flexion direction. Methods of use are also disclosed.

TECHNICAL FIELD

This invention relates generally to the actuator field, and more specifically to a new and useful actuator system with a motor assembly in the actuator field.

BACKGROUND

Motors and actuators are used in a wide variety of applications. Many applications, including robotics and active orthotics, require characteristics similar to human muscles. The characteristics include the ability to deliver high force at a relatively low speed and to allow free-movement when power is removed, thereby allowing a limb to swing freely during portions of the movement cycle. This may call for an actuator that can supply larger forces at slower speeds and smaller forces at higher speeds, or a variable ratio transmission (VRT) between the primary driver input and the output of an actuator.

VRTs have been conventionally implemented as Continuously Variable Transmissions (CVTs). The underlying principle of most previous CVTs is to change the ratio of one or more gears by changing the diameter of the gear, changing the place where a belt rides on a conical pulley, or by coupling forces between rotating disks with the radius of the intersection point varying based on the desired ratio. Prior art CVTs have drawbacks in efficiency and mechanical complexity.

Motors have been used in a variety of applications, but typically a single motor is directly or indirectly coupled to provide motion for each output direction. Use of a single motor limits the speed/torque range or requires the extra cost and complexity of a transmission between the motor and output. Thus, there is a need in the actuator field to create a new and useful actuator system that can supply larger forces at slower speeds and smaller forces at higher speeds, but that minimizes or avoids the disadvantages of the conventional CVTs. This invention provides such a new and useful actuator system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the invention is not intended to limit the invention to these preferred embodiments, but rather to enable any person skilled in the art of actuator systems to make and use this invention.

As shown inFIGS. 1 and 2, the actuator system100of the preferred embodiments for extending and flexing a joint110of a user includes a multi-motor assembly120for providing a rotational output, a rotary-to-linear mechanism150for converting the rotational output from the multi-motor assembly120into a linear motion that ultimately extends and flexes the joint, and a controller for operating the actuator system100in several operational modes. The multi-motor assembly120preferably combines power from two different sources, such that the multi-motor assembly120can supply larger forces at slower speeds (“Low Gear”) and smaller forces at higher speeds (“High Gear”). The actuator has been specifically designed for extending and flexing a joint110(such as an ankle, a knee, an elbow, or a shoulder) of a human or robot. The actuator system100may, however, be used to move any suitable object through any suitable movement (linear, rotational, or otherwise).

As shown inFIG. 2, the multi-motor assembly120of the preferred embodiments functions to provide rotational output to the rotary-to-linear mechanism150. The multi-motor assembly120includes a drive shaft122, a first motor subsystem124, and a second motor subsystem126. The drive shaft122functions to deliver the rotational output from the multi-motor assembly120. The first motor subsystem124functions to provide a component of the rotational output of the multi-motor assembly120. The first motor subsystem124includes a first motor128, a first output shaft130, and a first transmission132. The second motor subsystem126functions to provide another component of the rotational output of the multi-motor assembly120. The second motor subsystem126includes a second motor134, a second output shaft136, and a second transmission138.

The first motor128of the first motor subsystem124functions to provide a first source of power, and the first output shaft130functions to deliver this power to the other elements of the first motor subsystem124. The first motor128is preferably a three phase brushless electric motor with an outer rotor and seven pole pairs. The first motor128, which is preferably supplied by Hyperion under the model number G2220-14, has a peak current of 35 A and a peak power of 388 W. The first motor128may, of course, be a different type with different specifications and parameters depending on the design of the actuator system100.

The first transmission132of the first motor subsystem124functions to transmit the power from the first output shaft130to the drive shaft122. The first transmission132preferably includes two pulleys (one mounted on the first output shaft130and one mounted on the drive shaft122) and a belt or chain connecting the two pulleys. The first transmission132may alternatively include gears or any other suitable device or method that transmits the power from the first output shaft130to the drive shaft122. The first transmission132also preferably functions to define a first gear ratio of the rotation of the drive shaft122to the rotation of the first output shaft130. In the preferred embodiment, the pulley (or gear) mounted to the first output shaft130is smaller than the pulley (or gear) mounted to the drive shaft122, such that the first gear ratio is less than 1:1 (e.g., 1:4). In alternative embodiments, the first gear ratio may be 1:1 or may be greater than 1:1 (e.g., 4:1) depending on the design of the actuator system100.

The second motor134of the second motor subsystem126functions to provide a second source of power, and the second output shaft136functions to deliver this power to the other elements of the second motor subsystem126. The second motor134, like the first motor128, is preferably a three phase brushless electric motor with an outer rotor and seven pole pairs. The second motor134, which is preferably supplied by Hyperion under the model number G2220-14, has a peak current of 35 A and a peak power of 388 W. The second motor134is preferably identical to the first motor128in design and performance characteristics, which functions to reduce part count and manufacturing complexity. The second motor134may, however, be a different type with different specifications and parameters depending on the design of the actuator system100. The second output shaft136functions to deliver the power of the second motor134to the other elements of the second motor subsystem126.

The second transmission138of the second motor subsystem126functions to transmit the power from the second output shaft136to the drive shaft122. The second transmission138preferably includes two pulleys (one mounted on the second output shaft136and one mounted on the drive shaft122) and a belt or chain connecting the two pulleys. The second transmission138may alternatively include gears or any other suitable device or method that transmits the power from the second output shaft136to the drive shaft122. The second transmission138also preferably functions to at least partially define the second gear ratio of the rotation of the drive shaft122to the rotation of the second output shaft136. In the preferred embodiment, the pulley (or gear) mounted to the second output shaft136is smaller than the pulley (or gear) mounted to the drive shaft122, such that the second gear ratio is less than 1:1 (e.g., 1:4). In alternative embodiments, the second gear ratio may be 1:1 or may be greater than 1:1 (e.g., 4:1) depending on the design of the actuator system100.

The power from the first motor subsystem124and the power from the second motor subsystem126preferably have different characteristics, such that the multi-motor assembly120can supply larger forces at slower speeds (“Low Gear”) and smaller forces at higher speeds (“High Gear”). This may be accomplished by using different motors in the first motor subsystem124and the second motor subsystem126. In the preferred embodiment, however, this is accomplished by using identical motors, but with transmissions that define different gear ratios for the first motor subsystem124and the second motor subsystem126. The second gear ratio is preferably lower than the first gear ratio, but the actuator system100may be re-arranged such that the second gear ratio is higher than the first gear ratio.

The second transmission138of the second motor subsystem126preferably connects the second output shaft136to the first output shaft130. With this arrangement, the power from the second motor134is transmitted through both the second transmission138and the first transmission132before reaching the drive shaft122. Thus, the second transmission138and the first transmission132cooperatively define the second gear ratio. The effective gear ratio from motor134to the drive shaft122is a product of the first transmission132and the second transmission138. For example, if the gear ratios of both the first transmission132and the second transmission138were 1:3, then the effective gear ratio from motor134to the drive shaft122would be 1:9. By leveraging the first transmission132, this variation provides a compact form factor. Using the example, the system would be able to provide an effective gear ratio of 1:9 without the need for a large pulley or gear system.

As shown inFIG. 3, a second transmission238of a variation of the second motor subsystem226connects the second output shaft236to the drive shaft122. In this variation, the power from the second motor234is transmitted through only the second transmission238before reaching the drive shaft122(and, thus, the second transmission238defines the second gear ratio). By separately connecting the first motor128and the second motor234to the drive shaft122, the first gear ratio and the second gear ratio may be specifically tailored for the actuator system100.

As shown inFIG. 2, the multi-motor assembly120of the preferred embodiment also includes a one-way clutch140located between the second motor134and the drive shaft122. The one-way clutch140functions to facilitate the following motor modes:High Gear motor mode—the first motor subsystem124provides powers in a first direction without spinning the second output shaft136and imparting drag from the second motor subsystem126,Low Gear motor mode—the second motor subsystem126provides power in the first direction (with drag from the first motor subsystem124),Combined motor mode—the first motor subsystem124and the second motor subsystem126provide power in the first direction, andHigh Gear motor mode—the first motor subsystem124provides power in an opposite direction (with drag from the second motor subsystem126).

In a first variation of the multi-motor assembly120, as introduced above, the one-way clutch140is preferably located within the second transmission138and, more specifically, in the pulley mounted on the first output shaft130. In other variations, the one-way clutch140may be mounted in any suitable location between the second motor134and the drive shaft122.

The multi-motor assembly120of the preferred embodiment also includes a power source (not shown). The power source is preferably six lithium polymer battery cells, supplied by Emerging Power under the model number 603462H1. The battery cells are preferably arranged in both series and parallel (3S2P) to provide a voltage of 11.1V (nominal) and a capacity of 2640 maH. The power source may, however, be any suitable type, including both power supplied by the power grid and other portable sources (e.g., fuel cells), depending on the design of the actuator system100.

The rotary-to-linear mechanism150of the preferred embodiment functions to convert the rotational output from the multi-motor assembly120into a linear movement that ultimately extends and flexes the joint of the user. In the preferred embodiment, the rotary-to-linear mechanism150includes a ball screw152that accepts the rotational output of the multi-motor assembly120and a ball nut154that connects to the ball screw152and cooperates with the ball screw152to convert rotational movement of the ball screw152to linear movement of the ball nut154. The drive shaft122of the multi-motor assembly120and the ball screw152of the rotary-to-linear mechanism150are preferably different sections of the same shaft. One section includes a pulley (or gear) from the first transmission132, while another section includes a semi-circular, helical groove of the ball screw152. The drive shaft122and the ball screw152may, however, be separate shafts connected in any suitable manner, such as through a pulley or gear arrangement. In alternative embodiments, the rotary-to-linear mechanism150may include any suitable device or method that converts the rotational output from the multi-motor assembly120into an extension and flexion of the joint.

The rotary-to-linear mechanism150of the preferred embodiment also includes a linear slide156with a moving rail158that moves in a flexion direction and an extension direction. The linear slide156functions to provide a supported structure when the joint is fully flexed, and a compact structure when the joint is fully extended. The linear slide156preferably includes stationary wheels and moving wheels, but may alternatively include any suitable device or method to allow the moving rail158to move in the flex and extended directions.

As shown inFIGS. 2 and 4a, the moving rail158of the linear slide156preferably includes an extension stop160, which functions to translate linear movement of the ball nut154in an extension direction into an extension of the joint. In the preferred embodiment, the extension stop160is movable between a force position (shown inFIG. 2) that allows the ball nut154to apply force against the extension stop160, and a pass position (shown inFIG. 4a) that prevents the ball nut154from applying force against the extension stop160. In the force position, the extension stop160preferably applies a symmetric force to the ball nut154to avoid damaging or obstructing the ball nut. The extension stop160is preferably U-shaped and pivotally mounted on the moving rail158, but may alternatively be shaped and mounted in any manner to allow movement from the force position to the pass position. In an alternative embodiment, the extension stop160may be permanently (or semi-permanently) fixed or fastened in the force position.

In a first variation, as shown inFIGS. 2 and 4b, the moving rail158of the linear slide156also includes a flexion stop162, which functions to translate linear movement of the ball nut154in a flexion direction into a flexion of the joint. The flexion stop162is preferably movable between a force position (shown inFIG. 2) that allows the ball nut154to apply force against the flexion stop162, and a pass position (shown inFIG. 4b) that prevents the ball nut154from applying force against the flexion stop162. Like the extension stop160, the flexion stop162preferably applies a symmetric force to the ball nut154when in the force position, to avoid damaging or obstructing the ball nut. The flexion stop162, like the extension stop160, is preferably U-shaped and pivotally mounted on the moving rail158. In another variation, the flexion stop162is pivotally mounted on the extension stop160(as shown inFIG. 4d) to be movable between a force position (as shown inFIGS. 4dand4e) and a pass position. The flexion stop162may, however, alternatively be shaped and mounted in any manner to allow movement from the force position to the pass position. The flexion stop162may alternatively be permanently (or semi-permanently) fixed or fastened in the force position.

In a second variation, as shown inFIG. 4c, the moving rail158of the linear slide156may additionally or alternatively include a latch262, which functions to translate linear movement of the ball nut154in both the flexion and extension directions into a flexion and extension of the joint. In the preferred embodiment, the latch262includes a flexion stop surface and an extension stop surface. Similar to the flexion stop162in the first variation, the flexion stop surface of the latch functions to translate linear movement of the ball nut154in a flexion direction into a flexion of the joint. Similar to the extension stop160in the first variation, the extension stop surface of the latch functions to translate linear movement of the ball nut154in an extension direction into an extension of the joint. The latch262is preferably movable between an engaged position (shown inFIG. 4c) that allows the ball nut154to apply force against the extension stop surface and/or flexion stop surface of the latch to move the latch262and the moving rail, and a disengaged position (not shown) that prevents the ball nut154from applying force against the latch262. Similar to the extension stop160and flexion stop162in the force position, the latch262preferably applies a symmetric force to the ball nut154when in the engaged position, to avoid damaging or obstructing the ball nut. The latch262, unlike the extension stop160, is preferably mounted to engage and disengage in a slidable manner towards and away from the ball nut154The extension stop surface and flexion stop surface of the latch262preferably are sides of a rectangular side cutout262in the moving rail158(shown inFIG. 4f), into which an extended arm254coupled to the ball nut154engages and disengages in a slidable manner. The extended arm254, which is spring-loaded to default to the engaged position, slides into the side cutout to move into the engaged position, and slides out of the side cutout to move into the disengaged position. The latch262is preferably selected in the engaged position or disengaged position with a knob264(shown inFIG. 4f) coupled to the latch with a linkage mechanism266that pushes the extended arm254into the disengaged position and releases the extended arm254into the engaged position. The knob264is preferably movable between two discrete positions, one for latch engagement and one for latch disengagement, with the use of a ball plunger pressing against two discrete indentations, positioning a pin in one of a hole corresponding to latch engagement and a hole corresponding to latch disengagement, or any suitable mechanism.

The latch262may alternatively engage and disengage the ball nut154in a pivoting manner in a direction that is lateral to the moving rail158, or be shaped and mounted in any manner to allow movement from the engaged position to the disengaged position. The latch262may also alternatively be selected with a lever, manual handle, switch, an electronic switch, and/or any other suitable means of moving the latch between the engaged position and the disengaged position.

In another variation, the latch262is coupled to the ball nut154in an engaged position and free of the ball nut154in a disengaged position. Similar to the second variation, the latch262is movable between the engaged position and the disengaged position. When the latch262is in the engaged position, the latch262is coupled to the ball nut154such that linear movement of the nut in flexion and extension directions causes the latch262to move in flexion and extension directions and translate flexion and extension directions into a flexion and extension of the joint. When the latch262is in the disengaged position, the ball nut154moves independently of the latch262such that linear movement of the ball nut154does not cause the latch262to move.

In another variation, the flexion stop162and latch262may be omitted to allow unpowered flexion of the joint. In yet another variation, the extension stop160and flexion stop162may be omitted to allow unpowered extension and flexion of the joint.

The extension stop160and the flexion stop162are preferably located relatively far from each other, which allows the joint of the user to experience “free movement”, essentially moving the moving rail158back and forth between the extension stop160and the flexion stop162without the need to move the ball nut154or back-drive the multi-motor assembly120. In a variation, the extension stop160and the flexion stop162are located relatively close to each other, which prevents the joint of the user from experiencing little or no “free movement”. In other words, movement of the moving rail158will move the ball nut154and back-drive the multi-motor assembly120. Similar to the extension stop160and flexion stop162, the extension stop surface and flexion stop surface of latch262are preferably located relatively far from each other, but in a variation, the extension stop surface and flexion stop surface of the latch are located relatively close to each other.

As shown inFIG. 1, the actuator system100of the preferred embodiments for extending and flexing a joint110of a user includes a rotary-to-linear mechanism that functions to convert the linear movement of the moving rail into an extension and flexion (both rotational movements) of the joint of the user. In other variations, the actuator system100may include gears, pulleys, or any other suitable mechanism to ultimately extend and flex the joint of the user.

The controller of the preferred embodiment functions to operate the actuator system100in one of several operation modes. The controller preferably includes sensors to estimate the position of the moving rail158, and a sensor on the motor129to maintain the position of the ball nut154. Additional sensors estimate the force either provided by the multi-motor assembly120(for instance, via current sensors) or the total force applied to the joint via force sensors coupled to the thrust bearings (not shown) supporting drive shaft122. The controller may also include other sensors to predict or determine future forces applied to the joint or needed by the multi-motor assembly120. The controller may, however, use any suitable method or device to estimate the position of the moving rail158and the torque required from the multi-motor assembly120.

Based on the position of the moving rail158and the force needed by the multi-motor assembly120, the controller provides current to the first motor subsystem124, the second motor subsystem126, or both the first motor subsystem124and the second motor subsystem126. As shown inFIG. 5, the controller preferably operates the multi-motor assembly120of the actuator system100in the following operation modes: High Gear Flexion mode, High Gear Extension mode, Low Gear Extension mode, and Continuously Variable Transmission Extension mode.

In the High Gear Flexion mode, the controller provides current only to the first motor subsystem124such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150. The ball screw152is driven in the direction such that the ball nut154applies a force against the flexion stop162(if positioned in the force position) and drives the moving rail158in the flexion direction. The High Gear Flexion mode supplies a smaller force at a higher speed to quickly flex the joint of the user.

The High Gear Extension mode is similar to the High Gear Flexion mode, except the first motor subsystem124is driven in the opposite direction. In the High Gear Extension mode, the controller provides current only to the first motor subsystem124such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150and the ball nut154applies a force against the extension stop160. The ball screw152is driven in the direction such that the ball nut154applies a force against the extension stop160(if positioned in the force position) and drives the moving rail158in the extension direction. The High Gear Extension mode supplies a smaller force at a higher speed to quickly extend the joint of the user.

The Low Gear Extension mode is similar to the High Gear Extension mode, except the second motor subsystem126is driven instead of the first motor subsystem124. In the Low Gear Extension mode, the controller provides current only to the second motor subsystem126such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150and the ball nut154applies a force against the extension stop160. The ball screw152is driven in the direction such that the ball nut154applies a force against the extension stop160(if positioned in the force position) and drives the moving rail158in the extension direction. The Low Gear Extension mode supplies a larger force at a lower speed to forcefully extend the joint of the user.

In the Continuously Variable Transmission Extension mode, the controller provides current to both the first motor subsystem124and the second motor subsystem126such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150and the ball nut154applies a force against the extension stop160. In this mode, as exemplified inFIG. 6, the controller varies the ratio of current provided to the first motor subsystem124and current provided to the second motor subsystem126to achieve a desired rotational output in the Continuously Variable Transmission Extension mode. As the controller senses an increased force needed by the multi-motor assembly120, the controller preferably first ramps up the current to the first motor subsystem124(the High Gear or “HG”), then ramps down the current to the first motor subsystem124while ramping up the current to the second motor subsystem126(the Low Gear or “LG”). The Continuously Variable Transmission Extension mode can supply both a smaller force at a higher speed to quickly extend the joint of the user (“High Gear”), and a larger force at a lower speed to forcefully extend the joint of the user (“Low Gear”). More importantly, as shown inFIG. 7, by varying the ratio of current provided to the first motor subsystem124and current provided to the second motor subsystem126, the controller can achieve a desired force and speed from the multi-motor subsystem that is outside the range of possible forces and speeds supplied by just the first motor128or the second motor134. The actuator system100provides these advantages and features without providing a conventional multi-gear transmission or conventional CTV (with gears, conical pulleys, etc.).

As shown inFIG. 5, the controller of the preferred embodiment also operates the actuator system100in a Free Movement mode. In one variation of the Free Movement mode, the controller provides current to the first motor subsystem124such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150and the ball nut154moves away from the extension stop160. In another variation of the Free Movement mode, the controller provides current to the first motor subsystem124such that the multi-motor assembly120provides a rotational output to the rotary-to-linear mechanism150and the ball nut154maintains a general position between—but not contacting—the extension stop160or the flexion stop162.

As a person skilled in the art of actuator system100swill recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims. As a first example, while the actuator system100has been described to include a multi-motor assembly120with a first motor128and a second motor134, the multi-motor assembly120may include additional motors (with or without additional one-way clutches140). As an additional example, while the actuator system100has been described to include a rotary-to-linear mechanism150, it is possible that the rotational output of the multi-motor assembly120may be used without a mechanism that converts the rotational output to a linear output.