Patent Description:
In the field of mechanical machining, the positioning and position adjustment of a workpiece being processed are usually carried out by means of a robotic arm equipped with a gripper. Traditionally, telescopic cylinder-driven grippers and lead screw-driven grippers are used.

The telescopic cylinder-driven gripper includes two clamps and two telescopic cylinders that drive the two clamps to rotate respectively. The telescopic movement of each telescopic cylinder can control the movement of each clamp, so that the two clamps can be closed or opened. Due to the poor synchronization of the two telescopic cylinders, it is easy to cause the asynchronous movement of the two clamps, which will lead to poor gripping accuracy.

The lead screw-driven grippers can overcome the aforementioned problems of the telescopic cylinder-driven grippers. For example, in the grippers disclosed in Chinese patent <CIT>, two ends of the threaded portion of the lead screw are respectively provided with left-handed thread and right-handed thread, and a spacer is provided between the left-handed thread and the right-handed thread. A left gripping jaw is connected to the left-handed thread through a left-handed nut, and a right gripping jaw is connected to the right-handed thread through a right-handed nut. When such grippers grab objects, a motor drives the lead screw to move, and then the lead screw drives the left and right gripping jaws to move close to or move away from each other. Although such grippers have better synchronization between the left and right gripping jaws, the axial space occupied by the lead screw is too large, and the structures of the grippers and the gripper jaws thereof are not compact, causing the grippers to be too large and heavy. When large-size objects need to be grabbed, the use of such grippers not only causes a large load burden on the robotic arm, but also makes it difficult for the robotic arm to get into a small space for grabbing.

<CIT> discloses a mechanical claw, including an AC servo motor, a reduction gear, dual helical screws, screw nuts, connecting pressure plates, a first clamp, a second clamp, linear guides, and linear bearings. The AC servo motor is connected to the dual helical screws through the reduction gear, with two screw nuts fitted on the dual helical screws. The screw nuts are nested within central holes of the first and second connecting pressure plates. The first and second connecting pressure plates are respectively connected to the first and second clamps, which have a "<>" shaped structure. Two linear guides are each equipped with linear bearings nested within upper and lower holes of the first and second connecting pressure plates.

<CIT> discloses a device which makes possible the handling and manipulation of objects within a vessel. In a preferred embodiment there is provided a shaft, right and left hand intersecting threads on one end of said shaft, a pair of cooperating nuts having right and left hand threads respectively conforming with the right and left hand threads on said shaft and mounted on said shaft, cooperating object engaging means on said nuts, means for rotating said shaft and means for holding said nuts against rotation while the shaft rotates whereby the nuts move toward each other on rotation of the shaft in one direction and away from each other on rotation of the shaft in the opposite direction. Means are preferably provided to permit the rotation of the position of the nuts on the shaft whereby the position of the object engaging means may be changed from one plane to another.

<CIT> discloses a cable distribution line reel unwinding device, including an unwinding rack with a cable distribution device mounted on it. The cable distribution device includes a cable distribution bracket installed on the unwinding rack. Along the outer periphery of the cable distribution bracket, there are parallelly arranged guide shafts and reciprocating screws, both of which are parallel to the unwinding axis. The ends of the reciprocating screws are mounted on the cable distribution bracket through bearings, while the guide shaft is fixed to the cable distribution bracket. The reciprocating screws are equipped with bidirectional helical grooves, and a cable moving frame is connected between the guide shaft and the reciprocating screws. Both the guide shaft and the reciprocating screws pass through the cable moving frame. The cable moving frame has a driving pin engaging with the dual helical grooves. The cable moving frame slides in coordination with the guide shaft, and it is equipped with a guide sleeve on which guide holes are provided for cables to pass through from the cable distribution reel. This utility model enables the orderly arrangement of wires wound on the cable distribution reel, with a simple structure and convenient cable distribution.

TWI692388B discloses a gripper device which includes a belt pulley driven by a power-driven motor, a belt and another belt pulley driven by the above belt pulley, a ball screw driven and rotated by the belt pulley, nut brackets driven to be shifted along two rigid guideways by two reverse threads at both sides of the ball screw, respectively, and a plurality of steel balls, which are installed between a nut bracket and a rigid guideway and sustain more stresses when a workpiece is clamped between two upper slide on the nut brackets.

<FIG> show the structure of a gripper according to some embodiments of the present disclosure. As shown in <FIG>, the gripper includes a lead screw <NUM>, a first gripping jaw <NUM>, a second gripping jaw <NUM>, a first guiding mechanism 1a, and a second guiding mechanism 1b.

The lead screw <NUM> includes a spiral portion <NUM> and a driving portion <NUM>. The driving portion <NUM> can be located at either end or both ends of the spiral portion <NUM>. The spiral portion <NUM> is provided with two first spiral tracks <NUM> and two second spiral tracks <NUM>, and the first spiral tracks <NUM> and the second spiral tracks <NUM> are of opposite helical directions. Referring to <FIG>, the two first spiral tracks <NUM> are extending in parallel and spaced apart from each other in an axial direction of the lead screw <NUM>, and the two second spiral tracks <NUM> are extending in parallel and spaced apart from each other in the axial direction of the lead screw <NUM>. A first end of each first spiral track <NUM> corresponds to a first end of the spiral portion <NUM>, and a second end of each first spiral track <NUM> extends toward a second end of the spiral portion <NUM>. A second end of each second spiral track <NUM> corresponds to the second end of the spiral portion <NUM>, and a first end of each second spiral track <NUM> extends toward the first end of the spiral portion <NUM>. For example, the first end of each first spiral track <NUM> can be at the first end of the spiral portion <NUM>, and the second end of each second spiral track <NUM> is at the second end of the spiral portion <NUM>.

A portion of a coverage of the first spiral track <NUM> overlaps a portion of a coverage of the second spiral track <NUM> along a length of the spiral portion <NUM>. The section where coverage of the first spiral track <NUM> and the second spiral track <NUM> overlap may also be referred to as spiral cross section. As can be seen from the figures, in this embodiment, the second end of each first spiral tracks <NUM> extends to the second end of the spiral portion <NUM>, and the first end of each second spiral tracks <NUM> extends to the first end of the spiral portion <NUM>, so an axial length of the spiral portion <NUM> is equal to an axial length of the spiral cross section. That is, each first spiral track <NUM> and each second spiral track <NUM> respectively extends over an entire length of the spiral portion <NUM>. It should be understood that, in other embodiments, the second end of each first spiral track <NUM> may not extend to the second end of the spiral portion <NUM>, and/or the first end of each second spiral track <NUM> may not extend to the first end of the spiral portion <NUM>, so that the first spiral tracks <NUM> and the second spiral tracks <NUM> may partially overlap.

Both the first gripping jaw <NUM> and the second gripping jaw <NUM> are configured to be suitable for performing a linear movement in a direction parallel to the lead screw <NUM>. There are many implementations for making the first gripping jaw <NUM> and the second gripping jaw <NUM> perform the linear movement parallel to the lead screw <NUM>. In this embodiment, the first gripping jaw <NUM> is slidably connected to the first guiding mechanism 1a, and the first gripping jaw <NUM> performs a first linear movement under the guidance of the first guiding mechanism 1a. The second gripping jaw <NUM> is slidably connected to the second guiding mechanism 1b, and the second gripping jaw performs a second linear movement under the guidance of the second guiding mechanism 1b. The first guiding mechanism 1a and the second guiding mechanism 1b will be described in detail below.

The first gripping jaw <NUM> may have several first pins <NUM>. Some of the first pins <NUM> extend into the one of the first spiral tracks <NUM>, and other first pins <NUM> extend into the rest of the first spiral tracks <NUM>. Each first pin <NUM> is in sliding fit with the corresponding first spiral track <NUM>. That is, any one of the first spiral tracks <NUM> is slidably fitted with at least one of the first pins <NUM>. <FIG> shows an implementation structure of the first gripping jaw <NUM>, and the first pins <NUM> can be respectively installed in several pin holes <NUM> on the first gripping jaw <NUM>. In this way, when the lead screw <NUM> rotates, the first spiral tracks <NUM> pushes the first pins <NUM> to perform a linear movement parallel to the lead screw <NUM>, thereby driving the first gripping jaw <NUM> to perform the first linear movement parallel to the lead screw <NUM>. By providing these first pins <NUM>, it facilitates applying even force on the first gripping jaw <NUM>, realizing smooth movement of the first gripping jaw <NUM>.

In this embodiment, the structure of the second gripping jaw <NUM> may be similar to that of the first gripping jaw <NUM>. The second gripping jaw <NUM> has several second pins <NUM>. A portion of the second pins <NUM> extend into the one second spiral tracks <NUM>, and the other portion of the second pins <NUM> extend into the other second spiral tracks <NUM>. Each second pin <NUM> is in a sliding fit with the corresponding second spiral track <NUM>. That is, any one of the second spiral tracks <NUM> is slidably fitted with at least one of the second pins <NUM>. In this way, when the lead screw <NUM> rotates, the second spiral tracks <NUM> pushes the second pins <NUM> to perform a linear movement parallel to the lead screw <NUM>, thereby driving the second gripping jaw <NUM> to perform the second linear movement parallel to the lead screw <NUM>. It can be understood that the first movement direction of the first gripping jaw <NUM> is opposite to the second movement direction of the second gripping jaw <NUM>. By providing these second pins <NUM>, it facilitates applying even force applied on the second gripping jaw <NUM>, realizing smooth movement of the second gripping jaw <NUM>.

When the driving portion <NUM> of the lead screw <NUM> is driven to rotate, the driving portion <NUM> drives the spiral portion <NUM> to rotate together with the driving portion <NUM> either in a first direction or in a second direction opposite to the first direction. That is, the relative movement between the first gripping jaw <NUM> and the second gripping jaw <NUM> can be realized by the cooperation between the first pins <NUM>, the second pins <NUM> and the corresponding first spiral tracks <NUM>, the second spiral tracks <NUM>, respectively.

In some embodiments, when at least one first pin <NUM> is located at the first end of the corresponding first spiral track <NUM> (as long as there is one first pin <NUM> close to the first ends of the first spiral tracks <NUM>), and at least one second pin-<NUM> is located at the second end of the corresponding second spiral track <NUM> (as long as there is one second pin <NUM> close to the second ends of the second spiral tracks <NUM>), the first gripping jaw <NUM> and the second gripping jaw <NUM> are in a state of being far away from each other and the gripping distance between them is taken as the maximum gripping distance (that is, the first gripping jaw <NUM> and the second gripping jaw <NUM> are opened to the maximum extent), as shown in <FIG>.

According to an embodiment of the present disclosure, when the screw <NUM> is rotated, the first pins <NUM> is allowed to be moved from the first ends of the first spiral tracks <NUM> to the second ends of the first spiral tracks <NUM> (as long as there is one first pin <NUM> close to the second end of the corresponding first spiral track <NUM>), and the second pins <NUM> is allowed to be moved from the second ends of the second spiral tracks <NUM> to the first ends of the second spiral tracks <NUM> (as long as there is one second pin <NUM> close to the first end of the corresponding second spiral track <NUM>). At this time, the first gripping jaw <NUM> and the second gripping jaw <NUM> are in a state of being close to each other and the gripping distance between them is taken as the minimum gripping distance (the first gripping jaw <NUM> and the second gripping jaw <NUM> are closed to the minimum extent). In this embodiment, as shown in <FIG>, the minimum gripping distance is zero. In other embodiments, the minimum gripping distance may be greater than zero.

A portion of a coverage of the first spiral track <NUM> overlaps a portion of a coverage of the second spiral track <NUM> along a length of the spiral portion <NUM>. By properly configuring the first gripping jaw <NUM> and the second gripping jaw <NUM>, when the first pins <NUM> and the second pins <NUM> pass through the spiral cross section, it is possible to avoid the problem that the effective movements of the first spiral track <NUM> and the second spiral track <NUM> are shortened due to the interference between the first gripping jaw <NUM> and the second gripping jaw <NUM>. In this embodiment, the effective movement of the first gripping jaw <NUM> is substantially equal to an axial length of each first spiral track <NUM>, and the effective movement of the second gripping jaw <NUM> is substantially equal to an axial length of each second spiral track <NUM>, so that the sum of the effective movements of the first gripping jaw <NUM> and the second gripping jaw <NUM> is greater than an axial length of the spiral portion <NUM>, which can greatly reduce the axial length of the lead screw <NUM> and the space occupied by the lead screw <NUM> without reducing the stroke of the gripper. Thus, the implementation of the present disclosure may facilitate the miniaturization and compact design of the gripper, and reduce the weight of the gripper, while ensuring the maximum gripping distance between the first gripping jaw <NUM> and the second gripping jaw <NUM>.

It can be understood that, when the spiral portion <NUM> is consistent with the spiral cross section, the axial length of the lead screw <NUM> can be the shortest compared with other configurations. At this time, the sum of the effective movements of the first gripping jaw <NUM> and the second gripping jaw <NUM> is approximately twice the axial length of the spiral portion <NUM>. In addition, the speed of the change of the gripping distance between the first gripping jaw <NUM> and the second gripping jaw <NUM> is increased correspondingly.

It should be noted that although in this embodiment, there are two first spiral tracks <NUM> and two second spiral tracks <NUM>, in other embodiments, the number of the first spiral track <NUM> and the second spiral track <NUM> is not limited to two, for example, it may be one or more than two. In these cases, the number of the first pin <NUM> and the second pin <NUM> can be changed accordingly. In addition, the number of the first pin <NUM> extending into the same first spiral track <NUM> may be one, two or more. The number of the second pin <NUM> extending into the same second spiral track <NUM> may be one, two or more. Referring to <FIG>, in this embodiment, the number of the first pin <NUM> may be three, and the number of the second pin <NUM> may also be three.

In some embodiments, by properly arranging the positions of the first pins <NUM> on the first gripping jaw <NUM> and the positions of the second pins <NUM> on the second gripping jaw <NUM>, it is ensured that at least two first pins <NUM> are not at the intersections of the first spiral tracks <NUM> and the second spiral tracks <NUM> at the same time when they are moving along the first spiral tracks <NUM>, and at least two second pins <NUM> are not at the intersections of the first spiral tracks <NUM> and the second spiral tracks <NUM> at the same time when they are moving along the second spiral tracks <NUM>. In other words, the first spiral tracks <NUM> and the second spiral tracks <NUM> are configured such that the at least two first pins <NUM> arrive at intersections of the first spiral tracks <NUM> and the second spiral tracks <NUM> at different times during rotation of the spiral portion <NUM>, and similarly, the at least two second pins <NUM> arrive at the intersections of the first spiral tracks <NUM> and the second spiral tracks <NUM> at different times during rotation of the spiral portion <NUM>. In this way, it can be ensured that at least one first pin <NUM> and at least one second pin <NUM> are normally driven by the first spiral tracks <NUM> and the second spiral tracks <NUM> at any time during the rotation of the spiral portion <NUM>, without being affected by the intersections, and thus, the reliability of the movements of the first gripping jaw <NUM> and the second gripping jaw <NUM> can be ensured.

In an implementation, any adjacent two intersections of the first spiral tracks <NUM> and the second spiral track <NUM> are not in a same line on a surface of the spiral portion <NUM> that is parallel to an axis of the spiral portion <NUM>. Meanwhile, the first pins <NUM> are arranged in line with the arrangement of the pin hole <NUM> to which the first pins <NUM> are installed, and the second pins <NUM> are arranged in a similar way. By such configuration, the first pins <NUM> arrive at intersections of the first spiral tracks <NUM> and the second spiral track <NUM> at different times during rotation of the spiral portion <NUM>, and similarly, the second pins <NUM> arrive at intersections at different times during rotation of the spiral portion <NUM>.

Referring to <FIG> and <FIG>, some embodiments of the first gripping jaw <NUM> and the second gripping jaw <NUM> are shown in this embodiment. The first gripping jaw <NUM> includes a first gripping portion <NUM> and a first connecting portion <NUM>. A first end of the first connecting portion <NUM> is connected to the first gripping portion <NUM>, and a second end of the first connecting portion <NUM> protrudes laterally from the first gripping portion <NUM> and is suitable to be slidably connected to the first guiding mechanism 1a. The first pins <NUM> are provided at the second end of the first connecting portion <NUM>. The second gripping jaw <NUM> includes a second gripping portion <NUM> and a second connecting portion <NUM>. A first end of the second connecting portion <NUM> is connected to the second gripping portion <NUM>, a second end of the second connecting portion <NUM> protrudes laterally from the second gripping portion <NUM> and is suitable to be slidably connected to the second guiding mechanism 1b. The second pins <NUM> are provided at the second end of the second connecting portion <NUM>. The distance between the first gripping portion <NUM> and the second gripping portion <NUM> in the direction parallel to the lead screw <NUM> when the first gripping portion <NUM> and the second gripping portion <NUM> are located at their largest distance is referred to as the maximum gripping distance, and the gripper grasps or releases objects through the first gripping portion <NUM> and the second gripping portion <NUM>. In this embodiment, as shown in <FIG> and <FIG>, the first gripping portion <NUM> and the second gripping portion <NUM> are located at their largest distance and each is disposed outside the first and second ends of the spiral portion <NUM> when the maximum gripping distance is provided. As shown in <FIG> and <FIG>, the first gripping portion <NUM> and the second gripping portion <NUM> are located at their smallest distance and each is at the middle of the spiral portion <NUM> when the minimum gripping distance is provided.

In some embodiments, lengths of the first connecting portion <NUM> and the second connecting portion <NUM> in the direction parallel to an extending direction of the lead screw <NUM> can be adjusted. For example, the first connecting portion <NUM> and the second connecting portion <NUM> are respectively telescopic arms to meet various gripping requirements. In addition, in this embodiment, the first connecting portion <NUM> and the second connecting portion <NUM> may extend parallel to the lead screw <NUM>. It should be understood that, in other embodiments, the first connecting portion <NUM> and the second connecting portion <NUM> may extend, for example, obliquely with respect to the lead screw <NUM>.

The first connecting portion <NUM> can be slidably connected to the first guiding mechanism 1a in any suitable manner to guide the first gripping jaw <NUM> to perform the first linear movement in the direction parallel to the lead screw <NUM>. In the same way, the second connecting portion <NUM> can be slidably connected to the second guiding mechanism 1b in any suitable manner to guide the second gripping jaw <NUM> to perform the second linear movement in the direction parallel to the lead screw <NUM>. As described above, the moving direction of the first gripping jaw <NUM> and the moving direction of the second gripping jaw <NUM> are always opposite.

Some embodiments of the first guiding mechanism 1a and the second guiding mechanism 1b are also shown in this embodiment. The first guiding mechanism 1a includes a first linear guiding rail <NUM> and a first slider <NUM>, the first linear guiding rail <NUM> is parallel to the lead screw <NUM>, and the second end of the first connecting portion <NUM> is slidably connected to the first linear guiding rail <NUM> through the first slider <NUM>. For example, referring to <FIG>, the second end of the first connecting portion <NUM> is provided with several mounting holes <NUM>, and several fasteners (not shown) passing through the mounting holes <NUM> are connected to the first slider <NUM>, thereby fixing the second end of the first connecting portion <NUM> on the first slider <NUM>. The second guiding mechanism 1b includes a second linear guiding rail <NUM> and a second slider <NUM>, the second linear guiding rail <NUM> is parallel to the lead screw <NUM>, and the second end of the second connecting portion <NUM> is slidably connected to the second linear guiding rail <NUM> through the second slider <NUM>. In order to further optimize the structure of the gripper to make the gripper more compact, the lead screw <NUM> can be located between the first guiding mechanism 1a and the second guiding mechanism 1b, allowing the first gripping jaw <NUM> and the first guiding mechanism 1a are located on one side of the lead screw <NUM>, and the second gripping jaw <NUM> and the second guiding mechanism 1b are located on the other side of the lead screw <NUM>. In some embodiments, the lead screw <NUM> may be located between the first linear guiding rail <NUM> and the second linear guiding rail <NUM>.

In an embodiment not shown, the first guiding mechanism 1a may include a first guiding rod. The first guiding rod is parallel to the lead screw <NUM>, and the first connecting portion <NUM> is provided with a first hole that is slidably engaged with the first guiding rod. The second guiding mechanism 1b may include a second guiding rod. The second guiding rod is parallel to the lead screw <NUM>, and the second connecting portion <NUM> is provided with a second hole that is slidably engaged with the second guiding rod. In some embodiments, the lead screw <NUM> can be located between the first guiding rod and the second guiding rod.

It should be noted that there are many implementations of the first guiding mechanism 1a and the second guiding mechanism 1b, which are not limited to the above examples, as long as they can restrict the rotation of each of the first gripping jaws <NUM> and the second gripping jaws <NUM> relative to the lead screw <NUM>.

Referring to <FIG>, the gripper provided by this embodiment may further include a power mechanism <NUM>, and the power mechanism <NUM> is connected to the driving portion <NUM> of the lead screw <NUM>. The power mechanism <NUM> can drive the lead screw <NUM> to rotate in the first direction or in the second direction opposite to the first direction, so that the first pins <NUM> and the second pins <NUM> perform linear movements in the opposite direction to make the first gripping portion <NUM> and the second gripper portion <NUM> move toward or away from each other.

The power mechanism <NUM> may include a motor <NUM> and a reducer <NUM>, and the reducer <NUM> is connected between the motor <NUM> and the driving portion <NUM> of the lead screw <NUM>. Alternatively, as shown in this embodiment, the power mechanism <NUM> may include a motor <NUM>, a reducer <NUM> and a transmission mechanism <NUM>, and the power mechanism <NUM> may be mounted on the base <NUM>, for example. The motor <NUM> is connected to the reducer <NUM>, and they are located below the lead screw <NUM> together. The transmission mechanism <NUM> is used for transmitting the power output from the reducer <NUM> to the driving portion <NUM> of the screw <NUM>. The transmission mechanism <NUM> may be, for example, a chain transmission mechanism, a belt transmission mechanism, a gear transmission mechanism, or the like. The lead screw <NUM>, the motor <NUM>, and the reducer <NUM> are located on the same side of the transmission mechanism <NUM>. In this way, the structure of the gripper is more compact, and the axial space occupied by the gripper is smaller, which is more helpful for the gripper to enter a narrow space to grasp objects.

The present disclosure also provides an embodiment of a robotic arm including the above-mentioned gripper. Because the gripper of the present disclosure can achieve the above-mentioned technical effects, the robotic arm including the gripper can also achieve corresponding technical effects, and can reach into a narrow space for grasping objects.

In accordance with the embodiments of the present disclosure, the effective movement travel of the first gripping jaw is allowed to be substantially equal to an axial length of the first spiral track, and the effective movement travel of the second gripping jaw is allowed to be substantially equal to an axial length of the second spiral track, so that the sum of the effective movement travels of the first gripping jaw and the second gripping jaw is greater than an axial length of the spiral portion, which can greatly reduce the axial length of the lead screw and the space occupied by the lead screw on the basis of ensuring the maximum gripping distance between the first gripping jaw and the second gripping jaw, facilitating the miniaturization and compact design of the gripper, and facilitating to reduce the weight of the gripper.

The above-mentioned embodiments only describe a few implementations of the present disclosure, and the description is relatively specific and detailed, but they should not be interpreted as a limitation on the scope of the patent disclosure.

Claim 1:
A gripper, comprising:
a lead screw (<NUM>) comprising a spiral portion (<NUM>) and a driving portion (<NUM>), the spiral portion (<NUM>) being provided with at least one first spiral track (<NUM>) and at least one second spiral track (<NUM>) with opposite helical directions, wherein a first end of the first spiral track (<NUM>) corresponds to a first end of the spiral portion (<NUM>), and a second end of the first spiral track (<NUM>) extends toward a second end of the spiral portion (<NUM>), wherein a second end of the second spiral track (<NUM>) corresponds to the second end of the spiral portion (<NUM>), and a first end of the second spiral track (<NUM>) extends toward the first end of the spiral portion (<NUM>),
characterized in that:
a portion of a coverage of the first spiral track (<NUM>) overlaps a portion of a coverage of the second spiral track (<NUM>) along a length of the spiral portion (<NUM>); and
the gripper comprises a first gripping jaw (<NUM>) and a second gripping jaw (<NUM>), the first gripping jaw (<NUM>) having at least one first pin (<NUM>) extending into the first spiral track (<NUM>), and the second gripping jaw (<NUM>) having at least one second pin (<NUM>) extending into the second spiral track (<NUM>),
wherein the first gripping jaw (<NUM>) and the second gripping jaw (<NUM>) are configured in such a way that when the driving portion (<NUM>) drives the spiral portion (<NUM>) to rotate, the first spiral track (<NUM>) is configured to drive the first pin (<NUM>) to allow the first gripping jaw (<NUM>) to perform a first linear movement in a direction parallel to the lead screw (<NUM>), and the second spiral track (<NUM>) is configured to drive the second pin (<NUM>) to allow the second gripping jaw (<NUM>) to perform a second linear movement opposite to the first linear movement of the first gripping jaw (<NUM>).