JP2007166030A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device reducing a frictional load and an inertial load on a head and improving an operationality. <P>SOLUTION: The image display device has a main body being fitted to the head of a user and outputting an image and a supporter movably supporting the main body. In the image display device, the supporter has a supporting section movably supporting the main body while being synchronized with the movement of the head of the user and a detector detecting a force generated in response to the movement of the head of the user. In the image display device, the supporter further has a driver driving the supporter on the basis of the result of a detection detected by the detector. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention generally relates to a video display device, and more particularly to a head-mounted video display device having a support device that movably supports a video display device that can be mounted on a user's head or face. . Here, the head-mounted video display device (head-mounted display) displays video output from an external video player on a display mounted on the head or face.

  Due to the recent improvement in operability of electronic devices, improvement in operability is also required in video display devices. As a video display device, a head that is fixed to a user's head with a headband or the like, and a small liquid crystal panel or the like is used to enlarge the image on the panel as a virtual image by an eyepiece optical system and display it in front of the user's eyes An on-board video display device is known. Therefore, the head mounted video display device is required to have a viewing angle close to the viewing angle of the user, that is, a wide viewing angle. However, since an image display apparatus with a wide viewing angle has an enlarged optical system, the weight of the apparatus increases and the weight applied to the user's head increases.

In view of this, an image display device that reduces the weight applied to the user's head by supporting the main body with a support device such as an arm has been proposed (see, for example, Patent Document 1). There has also been proposed a video display device that detects the relative positional relationship between the user's head and the main body and moves the main body to a position where the user's head moves without being mounted on the user's head (for example, , See Patent Document 2).
Japanese Patent Application Laid-Open No. 08-125948 Japanese Patent Laid-Open No. 06-195440

  However, since the video display device of Patent Document 1 is connected to the arm, a load such as friction generated in the connecting portion of the arm is generated, and when the user's head moves, a resistance force is applied to the user's head. End up. In addition, the video display device disclosed in Patent Document 1 also gives the user resistance due to inertia. As a result, the video display device of Patent Document 1 has low operability.

  In addition, the video display device disclosed in Patent Document 2 detects a relative position with respect to the user without being fixed to the user's head with a headband or the like, and moves the main body in the moving direction of the user's head. For this reason, a deviation occurs in the reaction between the movement of the user's head and the movement of the main body. As a result, the video display device of Patent Document 2 gives the user a feeling that the image is blurred, and the operability is also low.

  Accordingly, an object of the present invention is to provide a video display device with high operability.

  An image display apparatus according to an aspect of the present invention is an image display apparatus including a main body that is mounted on a user's head and outputs an image, and a support device that movably supports the main body. Is detected by the detection unit, a support unit that supports the main body movably in synchronization with the movement of the user's head, a detection unit that detects a force generated according to the movement of the user's head And a drive unit that drives the support unit based on the detection result.

  Other objects or other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, a video display device with high operability can be provided.

  Hereinafter, a head-mounted image display apparatus 1 that is an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. Here, FIG. 1 is a perspective view showing a head-mounted image display device 1. FIG. 2 is a side view when the user 300 wears the head-mounted video display device 1.

  The video display device 1 projects a video on the user's retina. That is, the video display device 1 displays the video on a display panel 12 (described later) mounted on the head. The video display device 1 includes a main body 10 and a support device 100. In the present embodiment, the video display device 1 has a main body mounting portion 20 described later having a headband type shape, but may have various shapes such as a helmet type shape. However, it is preferable that the main body mounting portion is made as light as possible for the reasons described later. Furthermore, in the present embodiment, the video display device 1 can be provided with an audio output unit (not shown) that outputs audio. The video display device 1 may be controlled by a built-in controller or a remote controller.

  The main body 10 has a function of displaying an image on the display panel 12 mounted on the head. As illustrated in FIG. 3, the main body 10 includes a housing 11, a display panel 12, a prism lens 13, an imaging camera 14, and a main body mounting portion 20. The main body 10 further includes a power supply unit (not shown) and an external input unit. In this case, the power supply unit can have a built-in power supply or a power supply jack that supplies power from the outside. The external input unit may introduce an input signal of an external video player into the main body 10 and may include an image input unit and an audio input unit. Here, FIG. 3 is a configuration diagram showing the main body 10 of the video display device 1.

  The housing 11 has a function of protecting internal members and fixing it at a predetermined position. That is, the housing 11 accommodates and protects a display panel 12, a prism lens 13, and an imaging camera 14 to be described later. In this case, the casing 11 fixes a prism lens 13 and an imaging camera 14 (to be described later) in front of the eye 310 of the user 300, and fixes the display panel 12 on the prism lens 13. Further, the housing 11 is formed with an opening 11a as shown in FIG. The opening 11a is formed so that the imaging camera 14 described later captures an external image. The opening 11a may be covered with a shutter (not shown) when the operation of the main body 10 is finished. In addition, the housing 11 may be formed with a recess in the lower center portion in accordance with the shape of the face, and it is preferable to use a plastic material or the like for weight reduction. Further, the housing 11 may be configured to be divided from the center.

  The display panel 12 has a function of displaying an image. In this embodiment, a liquid crystal panel is used as the display panel 12. As shown in FIG. 3, the display panel 12 is displayed on the eye 310 of the user 300 via a prism lens 13 described later. Further, the image displayed on the display panel 12 can display not only a captured image of the imaging camera 14 described later but also an image from an external playback device.

  The prism lens 13 has a function of displaying an image from the display panel 12 at a predetermined position. As shown in FIG. 3, the prism lens 13 displays the image from the display panel 12 as a virtual image in front of the eyes 310 of the user 300. In addition, the prism lens 13 displays an image at a position where an optical axis center K of an imaging camera 14 (to be described later) coincides with a viewing direction J of the user 300. Thereby, the main body 10 can make the user 300 feel as if the user sees the external world image with his / her own eyes.

  The imaging camera 14 has a function of capturing an external image, and includes a lens 14a and an imaging element 14b. In the imaging camera 14, the optical axis center K coincides with the line-of-sight direction J of the user 300.

  The lens 14a has a function of condensing light from the outside onto an image sensor 14b described later. For example, a biconvex lens is used as the lens 14a. In the present embodiment, there is one lens 14a, but there may be a plurality of lenses.

  The image sensor 14b converts the light from the lens 14a into an electrical signal. The image sensor 14b is disposed closer to the eye 300 of the user 300 than the lens 14a.

  The main body mounting unit 20 has a function of mounting the main body 10 on the head of the user 300. The main body mounting portion 20 is made of a plastic material for weight reduction. The main body mounting unit 20 includes a size adjusting unit (not shown), and can be adjusted according to the size of the user's 300 head. The main body mounting unit 20 includes a front mounting unit 21, a rear mounting unit 25, and a buffer member 30.

  The front mounting part 21 is used for mounting the main body 10 on the head of the user 300. The front mounting portion 21 has a U shape and is connected to a rear mounting portion 25 described later. In this case, the connection part of the front side mounting part 21 and the rear side mounting part 25 may even be connected so that adjustment is possible. In addition, the front mounting portion 21 is provided with a front buffer member 31 described later at a position in contact with the forehead of the user 300. Further, the front mounting portion 21 is connected to the first support portion 111 via a detection portion 130 described later.

  The rear mounting part 25 is used for mounting the main body 10 on the head of the user 300. The rear mounting portion 25 is U-shaped and is connected to the front mounting portion 21. Further, the rear mounting portion 25 may have an adjustment portion (not shown) that can adjust the size. Further, the rear mounting portion 25 may be an elastic member that can be expanded and contracted, and thereby the length of the rear mounting portion 25 may be adjusted. The rear mounting portion 25 is formed with a rear buffer member 33 described later.

  The buffer member 30 has a function of absorbing a pressing force from the head of the user 300. The buffer member 30 includes a front buffer member 31 and a rear buffer member 33.

  The front buffer member 31 has a function of absorbing a pressing force from the head of the user 300. The front buffer member 31 is made of an elastic member and is formed in the front mounting portion 21.

  The rear buffer member 33 has a function of absorbing a pressing force from the head of the user 300. The rear buffer member 33 is made of an elastic member and is formed in the rear mounting portion 25.

  The support device 100 supports the main body 20 and the main body mounting portion 20 and moves the main body 10 according to the movement of the head of the user 300, and thus the movement of the main body mounting portion 20. The support device 100 includes a support unit 110, a drive unit 120, a detection unit 130, a control unit 140, and a support shaft drive mechanism 150.

  The support part 110 has a function of supporting the main body 10 and the main body mounting part 20. In the present embodiment, the support unit 110 supports the video display device 1 so as to be movable. In addition, the support part 110 includes a first support part 111, a second support part 116, and a support shaft 117.

  The first support part 111 is used to support the main body 10 and the main body mounting part 20. The first support portion 111 has a U shape and is connected to the front mounting portion 21 via a right detection portion 131, a left detection portion 133, and a front detection portion 135, which will be described later. The first support part 111 is directly connected to the housing 11. Further, the first support portion 111 is disposed on the outer periphery of the front mounting portion 21.

  The second support part 116 is used to support the main body 10, the support part 111, and the main body mounting part 20. The second support part 116 is U-shaped, and is connected to the first support part 111 via a right drive part 121 and a left drive part 123 which will be described later. Further, the second support portion 116 is connected to the support shaft 117 via an upper drive portion 125 and a second upper drive portion 127 described later.

  The support shaft 117 is used to support the main body 10, the support part 111, the support part 116, and the main body mounting part 20. One end of the support shaft 117 is connected to the second support unit 116 via an upper drive unit 125 and a second upper drive unit 127 described later, and the other end is movable in the horizontal plane X, Y direction, and vertical direction Z. Connected to a driving unit 150. Here, X, Y, and Z are orthogonal coordinates fixed in space based on the moving direction of the driving unit 150, and are a global coordinate system described later.

  The drive unit 120 has a function of driving the main body 10 according to the movement of the user's 300 head. That is, the drive unit 120 drives the main body 10 based on a detection result by the detection unit 130 described later. In the present embodiment, the drive unit 120 is a motor and incorporates an encoder for detecting the rotational position. The drive unit 120 includes a right drive unit 121, a left drive unit 123, an upper drive unit 125, and a second upper drive unit 127.

  The right drive unit 121 and the left drive unit 123 have a function of rotating the main body 10 according to the movement of the head of the user 300. That is, the right drive unit 121 and the left drive unit 123 rotate the main body 10 based on the detection result by the detection unit 130 described later. The rotation axes of the right drive unit 121 and the left drive unit 123 are parallel to the x direction of a local coordinate system x, y, z, which will be described later, indicating the position of the video display device 1 in space with respect to the global coordinate system. This rotational direction is defined as θx. Moreover, as shown in FIG. 4, the right side drive part 121 and the left side drive part 123 are electrically connected with the control part 140 mentioned later. Here, FIG. 4 is a block diagram showing a configuration of the support device 100.

  The upper drive unit 125 has a function of driving the main body 10, the supports 111 and 116, and the main body mounting unit 20 according to the movement of the head of the user 300. That is, the upper drive unit 125 drives the main body 10, the supports 111 and 116, and the main body mounting unit 20 based on the detection result of the detection unit 130 described later. The rotation axis of the upper drive unit 125 is parallel to the Z direction of the global coordinate system described later. This rotation direction is defined as θz. Moreover, the upper side drive part 125 is electrically connected to the control part 140, as shown in FIG. Further, the upper drive unit 125 is disposed on the top of the second support unit 116.

  The second upper drive unit 127 has a function of driving the main body 10, the support units 111 and 116, and the main body mounting unit 20 according to the movement of the head of the user 300. That is, the second upper drive unit 127 drives the main body 10, the support units 111 and 116, and the main body mounting unit 20 based on the detection result of the detection unit 130 described later. The rotation axis of the second upper drive unit 127 is parallel to the Y direction of the global coordinate system described later. This rotational direction is defined as θy. The second upper drive unit 127 is electrically connected to the control unit 140 as shown in FIG. Further, the second upper drive unit 127 has one end connected to the upper drive unit 125 and the other end connected to the support shaft 117. In addition, the drive part 120 may drive the main body mounting part 20 with a gas pressure or a spring, not a motor.

  The detection unit 130 detects the force generated according to the movement of the user's 300 head. In this embodiment, the detection unit 130 includes a pressure sensor such as a piezoelectric element. In this case, the detection unit 130 is electrically connected to the control unit 140 and transmits a detection signal to the control unit 140, as shown in FIG. The detection unit 130 includes a right detection unit 131, a left detection unit 133, and a front detection unit 135.

  The right detection unit 131 detects a load generated according to the movement of the user's 300 head. In the present embodiment, the right detection unit 131 is a first detection unit that detects a load generated in the x direction of x, y, and z in the local coordinate system described later, and a second detection unit that detects a load generated in the Y direction. And a third detection unit for detecting a load generated in the Z direction. As shown in FIG. 5, the right detection unit 131 includes members 131a, 131b, 131c, and 131d, and piezoelectric elements 131e, 131f, and 131g. Here, FIG. 5 is a cross-sectional view showing a cross section AA of the detection unit 130.

  The member 131a is formed integrally with the first support portion 111. The member 131b is fitted into the member 131a so as to be movable in the arrow direction B (x-axis direction). As shown in FIG. 6, the member 131c is fitted into the member 131b so as to be movable in the arrow direction C (z-axis direction). The member 131d is fitted into the member 131c so as to be movable in the arrow direction D (y-axis direction). The member 131d is formed integrally with the front mounting portion 21. Here, FIG. 6 is a cross-sectional view showing a cross-section BB of the right detection unit 131.

  The piezoelectric elements (mechanical / electrical conversion elements) 131e to 131g have a function of converting the force generated by the movement of the user's 300 head into electricity. In the present embodiment, piezoelectric elements such as piezoelectric elements are used as the piezoelectric elements 131e to 131g. The piezoelectric element 131e is disposed between the cylindrical portion 131a and the member 131b, and converts pressure in the arrow direction B (x-axis direction) into electricity. The piezoelectric element 131f is disposed between the member 131b and the member 131c, and converts pressure in the arrow direction C (z-axis direction) into electricity. The piezoelectric element 131g is disposed between the member 131c and the member 131d, and converts pressure in the arrow direction D (y-axis direction) into electricity.

  The left side detection unit 133 detects a force generated according to the movement of the user's 300 head. The configuration of the left detector 133 is the same as that of the right detector 131 except that it does not have a detection function in the arrow direction B (x-axis direction), and thus the description thereof is omitted.

  The front detection unit 135 detects a force generated according to the movement of the head of the user 300. The front detection unit 135 includes a third detection unit that detects a force generated in the z-axis direction. As shown in FIG. 7, the front side detection unit 135 includes members 135a, 135b, and 135c, and a piezoelectric element 135d. Here, FIG. 7 is a cross-sectional view showing a cross section CC of the front side detection unit 135.

  The member 135a is formed integrally with the main body 10. The member 135b is fitted into the member 135a so as to be movable in the horizontal direction. The member 135c is fitted into the member 135b so as to be movable in the vertical direction.

  The piezoelectric element (mechanical / electrical conversion element) 135d has a function of converting the force generated by the movement of the user's 300 head into electricity. The piezoelectric element 135d is disposed between the member 135b and the member 135c, and converts the pressure in the z-axis direction into electricity.

  In the present embodiment, the detection unit 130 uses a piezoelectric element. However, the detection unit 130 may detect a movement of the head of the user 300 using a strain electric element.

  The control unit 140 controls the operation of the support device 100. As shown in FIG. 4, the control unit 140 is electrically connected to the drive unit 120 and the detection unit 130. The control unit 140 includes an arithmetic circuit such as an MPU (microprocessor unit). In this case, the control unit 140 may be built in the main body 10 or a control device (not shown) that is electrically connected to the support device 100.

  The support shaft drive mechanism 150 has a function of supporting the support shaft 117 so that it can be driven. The support shaft driving mechanism 150 is fixed by a fixing unit (not shown) such as a ceiling or is movably fixed. The spindle drive mechanism 150 can drive in the global coordinate system X, Y, and Z directions, which will be described later, in space. Further, the support shaft driving mechanism 150 may drive the support shaft 117 not only by a motor but also by a spring, gas pressure, or the like.

  Thus, when the user's head moves, the video display device 1 can reduce the load caused by friction or the like caused by the movement of the display device or the load caused by inertia. That is, since the resistance to the user's head can be reduced, the operability can be improved. In addition, since the video display device 1 is fixed to the user's head, the operability can be improved without giving the user a feeling that the image is blurred.

  Hereinafter, the operation of the control unit 140 will be described.

  First, Cartesian coordinates fixed on a space based on the moving direction of the support shaft 117 are defined as a global coordinate system, which is X, Y, and Z. In addition, the orthogonal coordinates indicating the positional relationship with respect to the global coordinate system of the video display device 1 are defined as x, y, z as the local coordinate system.

  Here, for convenience of explanation, the axial directions of the local coordinate systems x, y, and z are made to substantially coincide with the detection directions of the loads by the rotation axes of the drive units 121 and 123 and the piezoelectric element 131e. The y axis is parallel to the load detection direction of the piezoelectric element 131g and the piezoelectric element (not shown) in the same direction in the left detection unit, and the z axis is the detection direction of the piezoelectric element (not shown) in the same direction of the piezoelectric elements 131f and 135d and the left detection unit. To be parallel to

  In the right detection unit 131, the load in the x direction detected by the piezoelectric element 131e is Fax, the load in the y direction detected by the piezoelectric element 131g is Fay, and the load in the z direction detected by the piezoelectric element 131f is Faz. Similarly, let the load in the y direction detected by the piezoelectric element in the left detection unit 133 be Fby, and the load in the z direction be Fbz. Further, a load in the z direction detected by the piezoelectric element 135d in the front side detection unit 135 is defined as Fcz. When the wearer wears the video display device 1 in a horizontal state as shown in FIG. 1 and moves his / her head parallel to the X-axis direction with respect to the global coordinate system, the right detection unit 131 detects the load Fax. The controller 140 drives the support shaft 117 in the X direction in the global coordinate system so that the detected load Fax becomes zero. When the movement of the head of the wearer and the movement of the support shaft 117 are synchronized, the load Fax becomes zero. At this point, the control unit 140 stops driving the spindle 117. However, since the load Fax is detected again when the wearer continues to move the head, the control unit 140 drives the support shaft 117 again in the same direction. When the movement of the wearer's head stops, the load Fax becomes zero accordingly, and the control unit 140 stops driving the support shaft 117.

  When the wearer similarly moves the head parallel to the Y-axis direction, the control unit 140 drives the support shaft 117 so that the loads Fay and Fby detected by the respective detection units become zero. When moved in parallel to the Z-axis direction, similarly, the support shaft 117 is moved so that the loads Faz, Fbz, and Fcz in the Z-axis direction detected by the respective detection units become zero.

  When the wearer rotates the head around the x axis, that is, in the θx direction, loads Faz, Fbz, and Fcz in the z direction are detected by the respective detection units. The rotational force generated around the x axis is obtained from these loads. The control unit 140 rotates the right drive unit 121 and the left drive unit 123, which are motors, and controls the generated rotational force to be 0, and thus the loads Faz, Fbz, and Fcz to be 0.

  When the wearer rotates his / her head around the z-axis, that is, in the θz direction, Fay is detected by the right detector and Fby is detected by the left detector, and the rotational force generated around the z-axis is obtained from these loads. . The control unit 140 controls the drive unit 125 such as a motor to rotate so that the generated rotational force is zero, and thus the loads Fay and Fby are zero.

  When the wearer tilts his / her head around the y-axis, the loads Faz and Fbz are detected by the right detection unit 131 and the left detection unit 133, respectively. At the same time, the load Fax in the x-axis direction is detected by the displacement of the rotation axis on the mechanism. The control unit 140 rotates the driving unit 127 made of a motor or the like in the θy direction so that the loads Faz and Fbz become zero. At the same time, the support shaft 117 is moved in the X direction in the absolute coordinate system so that the load Fax becomes zero.

  For example, when the wearer moves his / her head in the vertical direction or the horizontal direction while being tilted to some extent around θx, the rotational position is detected by an encoder provided in each of the drive units 131, 125, and 127. Then, the directions of the loads Fax, Fay, Faz, Fby, Fbx, and Fcz in the local coordinate system are decomposed into X, Y, and Z directions in the global coordinate system based on the value. Based on the value, the control unit 140 controls the rotation of the respective drive units 131, 133, 125, and 127 and the movement of the support shaft 117 in the global coordinate system X, Y, and Z directions by the support shaft drive mechanism 150.

  As described above, when the video display device 1 is mounted via the main body mounting portion 20 and the wearer moves the head in an arbitrary direction, each load is detected by the piezoelectric element corresponding to that direction. On the other hand, the inclination of the local coordinate system x, y, z with respect to the global coordinate system X, Y, Z of the video display device 1 is obtained by the control unit 140 from the encoders provided in the drive units 121, 125, 127. Therefore, the control unit 140 obtains a load direction and a rotational moment acting on the video display device 1 by mechanical calculation from the loads Fax, Fay, Faz, Fby, Fbz, Fcz and the inclination of the video display device 1. From these obtained values, the drive units 121, 123, 125, 127 are rotationally driven so that the rotational moment becomes zero. With respect to the load, the support shaft 117 is driven by the support shaft driving mechanism 150 so that the load becomes zero in the X, Y, and Z directions.

  Here, when the video display device is not mounted as shown in FIG. 1 and is supported in a horizontal state, for example, the load of the main body mounting portion 20 acts in the vertical direction (z-axis direction) due to gravity. However, since this load can be regarded as practically 0 by making the mounting mechanism light, it is possible to prevent the drive unit from moving without being mounted.

  In the above-described example, three detection units are provided between the support unit 111 that supports the main body 10 and the mounting unit 20, but only one unit may be used as long as a load in the direction of six degrees of freedom can be detected.

  As described above, the control unit 140 calculates the direction from the load value detected corresponding to the movement of the wearer's head, and drives each drive unit so that the value becomes zero. Thus, the load received when the wearer moves the display device 1 is reduced. In particular, by providing a load detection unit between the video display device 1 and the main body mounting unit 20, the load acting on the head is limited to the main body mounting unit 20 that can be reduced in weight. That is, the frictional load and inertial load on the head due to a mechanically large portion such as the image display device and the support portion are reduced.

  Thus, when the user's head moves, the video display device 1 can reduce the resistance to the user's head, and thus can improve operability. In addition, since the video display device 1 is fixed to the user's head, the operability can be improved without giving the user a feeling that the image is blurred.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof.

1 is a schematic perspective view showing a head-mounted image display device of the present invention. FIG. 2 is a schematic side view when the user wears the head-mounted video display device shown in FIG. 1. It is a schematic block diagram which shows the main body of the video display apparatus shown in FIG. It is a schematic block diagram which shows the structure of the support apparatus shown in FIG. It is a schematic sectional drawing which shows the cross section AA of the detection part shown in FIG. It is a schematic sectional drawing which shows the cross section BB of the right side detection part shown in FIG. It is a schematic sectional drawing which shows the cross section CC of the front side detection part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Video display apparatus 10 Main body 11 Housing | casing 12 Display panel 13 Prism lens 14 Imaging camera 20 Main body mounting part 30 Buffer member 100 Support apparatus 110 Support part 120 Drive part 130 Detection part 140 Control part 150 Support shaft drive mechanism

Claims (6)

A video display device having a main body that is mounted on a user's head and outputs an image, and a support device that movably supports the main body,
The support device includes a support unit that supports the main body so as to be movable in synchronization with the movement of the user's head.
A detection unit for detecting a force generated according to the movement of the user's head;
An image display apparatus comprising: a drive unit that drives the support unit based on a detection result detected by the detection unit.   The video display device according to claim 1, wherein the detection unit is formed between the video display device and a mounting unit that fixes the video display device to a user's head.   The video display device according to claim 1, wherein the detection unit includes a mechanical / electrical conversion element that electrically converts a force generated according to a movement of the head of the user.   The video display according to claim 1, wherein the detection unit includes an encoder that detects a drive amount of the drive unit, and is configured to detect a displacement in an arbitrary direction on a space of the video display device. apparatus.   The video display apparatus according to claim 1, wherein the driving unit is configured to be able to move the video display apparatus in an arbitrary direction in space.   The video display device according to claim 1, wherein the support device further includes a control unit that drives the drive unit in a direction in which the force is generated and controls the drive so that the force becomes substantially zero.