JP4460561B2 - Obstacle detection device for stair elevator - Google Patents

Description

  The present invention relates to an obstacle detection device for a stair lift that moves up and down along a staircase or a ramp of a building.

  Prior art stair lifts are used to assist users such as the elderly, the sick, and the disabled to move between lower and upper floors of buildings such as welfare facilities and homes. It is installed on the wall facing the stairs. Such a stair lift includes a guide rail provided parallel to the staircase, a ramp or a wall facing the staircase along the staircase, a lift main body that travels in the upward and downward directions along the guide rail, and a lift main body. Including chairs to be mounted. A user can move between the upper floor and the lower floor by sitting on this chair and running the elevator body in the upward or downward direction along the guide rail (see, for example, Patent Document 1).

JP 2004-307206 A

  In the prior art stair lift, in order to improve safety, when the lift main body collides with an obstacle during travel, the travel is automatically stopped. However, if the elevator main body collides with an obstacle during traveling, the elevator main body stops after the collision, so that an impact at the time of collision occurs on the collided obstacle. If the obstacle is a stairs user, there is a risk of injury to the stairs user.

  Therefore, an object of the present invention is to provide an obstacle detection device for a stair lift that can stop traveling when it collides with an obstacle during traveling and can reduce the impact on the obstacle as much as possible, thereby improving safety. Is to provide.

The present invention includes a portable machine that travels along a guide rail installed on a building stairs, a ramp, or a wall facing the stairs,
Drive means for driving the carrier along the guide rail;
Buffer means having flexibility, provided at both ends in the width direction of the carrier and at the lower part of the carrier so as to protrude from the carrier in the traveling direction of the carrier,
A detecting means provided in each of the buffering means for detecting a change in the shape of the buffering means;
Control means for controlling the drive means to stop the movement of the transporter when the change in the shape of the buffer means is detected by the detection means and the information given from the detection means is larger than a predetermined threshold value ; only including,
The control means detects the change in the shape of the buffer means downstream in the movement direction by the detection means provided in the buffer means downstream in the movement direction, and the movement direction is within the period in which the movement of the carrier is stopped. When the detecting means provided in the downstream buffer means detects that the shape of the buffer means downstream in the movement direction has returned to the shape before the change, the drive means is controlled to resume the movement of the transporter And
When the amount of deformation per unit time of the buffer means downstream in the movement direction is large, the control means shortens the time until the drive means completely stops, and the buffer means downstream of the movement direction When the deformation amount per unit time is small , the obstacle detecting device for a stair lift is characterized in that control is performed so as to lengthen the time until the driving means completely stops .

In the present invention, the buffer means includes a buffer material having charging properties,
The detection means is a sensor that detects a capacitance that changes due to a change in the shape of the buffer means.

According to the present invention, the transporter is driven to travel along the guide rail by the driving means. This allows the transporter to move up and down between the upper and lower floors of the building. Therefore, a load and a transported object such as a person can be transported by placing the load on the transport device or by the user getting on the transport device. The transporter is provided with buffer means having flexibility, provided at both ends in the width direction of the transporter and at the lower part of the transporter so as to protrude from the transporter in the traveling direction. Therefore, if there is an obstacle in the movement path while the transporter is moving, the shock absorber will have flexibility when it collides with the obstacle. Therefore, the damage to the obstacle due to deformation is minimized. can do. The control means controls the drive means so as to stop the movement of the transporter when the change in the shape of the buffer means is detected by the detection means and the information given from the detection means is larger than a predetermined threshold value. . Therefore, when the shape of the flexible buffer means changes when an obstacle collides with the buffer means, this change is detected by the detection means, and the movement of the transporter is stopped by the control means. As a result, when the vehicle collides with an obstacle, damage to the obstacle can be made as small as possible, and the movement of the transporter can be automatically stopped. Thereby, even if the obstacle is a person, the transporter can be safely stopped without causing injury to the person. As a result, the safety of the stair lift can be improved. In addition, the control means detects the movement within a period in which the change of the shape of the buffering means on the downstream side in the moving direction is detected by the detecting means provided on the buffering means on the downstream side in the moving direction and the movement of the carrier is stopped. When it is detected by the detecting means provided in the buffering means on the downstream side in the direction that the shape of the buffering means on the downstream side in the moving direction has returned to the shape before the change, the driving means is set so as to resume the movement of the carrier. Control. In addition, when the amount of deformation per unit time of the buffer means on the downstream side in the movement direction is large, the control means shortens the time until the drive means completely stops, and the buffer means on the downstream side in the movement direction When the deformation amount per unit time is small, control is performed so as to lengthen the time until the driving means completely stops.

  According to the invention, the buffer means includes a buffer material having charging properties, and the detection means is a sensor that detects a capacitance that changes due to a change in the shape of the buffer means. Therefore, the buffer means can be configured so that the capacitance detected by the detecting means changes when an external force acts on the buffer means and the shape of the buffer means changes. As a result, the detection means can reliably detect a change in the shape of the buffer means. Therefore, the safety of the stair lift can be further improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a front view showing a stair lift 1 according to an embodiment of the present invention. FIG. 2 is a plan view showing the stair lift 1. FIG. 3 is a side view showing the stair lift 1. In FIG. 1 to FIG. 3, buffer parts 2 a to 2 c provided in the stair lift 1 are virtually shown for easy understanding. The stair lift 1 is a device that enables a person and an object to be transported along the stairs 3 to move between an upper floor and a lower floor. The user of the stair lift 1 may be a healthy person, such as a physically handicapped person with a disability in spontaneous movement and a handicapped person with an involuntary movement in which the body moves without depending on the intention of the person. Target non-healthy people with movement disorders in at least lower limbs. The stair lift 1 includes a guide rail 4, a lift main body 5, a chair 6, buffer units 2 a to 2 c, a sensor unit 7, an operation input unit 8, a control unit 9, and a drive device 10.

  The guide rail 4 is a rail that guides the elevator body 5 across the upper and lower floors, and is provided along the stairs 3 of the building 3a. The guide rail 4 is fixed to the stairs 3 between the lower floor and the upper floor of a building 3a such as a house and a nursing home. The guide rail 4 is fixed at a position close to the substantially vertical wall 3b facing the stairs 3. The elevator body 5 is mounted on the guide rail 4 so as to be able to travel along the direction in which the guide rail 4 extends. The guide rail 4 supports the elevator main body 5 and each part mounted on the elevator main body 5, for example, the chair 6, the buffer units 2a to 2c, the sensor unit 7, the operation input unit 8, the control unit 9, the driving device 10, and the object to be conveyed. Has possible rigidity.

  The elevator body 5 is a portable machine and travels along the guide rail 4. The elevator body 5 is mounted on the guide rail 4 and supports each part mounted on the elevator body 5. The elevator body 5 is mounted on the guide rail 4 and is movable along the guide rail 4 in the directions of arrows A1 and A2. The elevator body 5 incorporates a driving device 10 that functions as a driving means. The drive device 10 includes a plurality of unillustrated rollers for sandwiching the guide rail 4 from both the left and right sides, and a sprocket. The elevator body 5 selects the sprocket for the guide rail 4 in either the ascending direction A1 or the descending direction A2. And a rotational drive source that is rotationally driven. The rotational drive source includes an electric motor and a speed reducer that decelerates the rotation of the electric motor to a predetermined rotational speed, and transmits the rotational force decelerated by the speed reducer to a chain disposed on the upper portion of the guide rail 4 for guidance. It is comprised so that it can drive | work to the arrow A1, A2 direction along the rail 4. FIG.

  The chair 6 is provided in the elevator body 5 and is configured so that a user can be seated. Such a chair 6 allows the user to move between the lower floor and the upper floor by moving the elevator body 5 while the user is seated. The chair 6 is connected to a base 11 fixed on the horizontal upper surface of the elevator body 5 and is connected to the base 11 so as to be able to rotate in the directions of arrows B1 and B2 around a horizontal first axis L1. The base plate 11 has a lower end connected to the side of the base 11 closer to the wall, supports the back of the user, and both sides of the base plate 11 in the width direction at both ends of the base 11 in the width direction. And a pair of armrest members 14 pivotally supported in the directions of arrows B1 and B2 around the first axis L1.

  The buffer parts 2a to 2c are buffer means and have flexibility, and when the elevator body 5 collides with an obstacle during movement, the elevator is designed to minimize damage to the obstacle as much as possible. Provided on the main body 5. When there is an obstacle on the moving path of the elevator body 5, the buffer parts 2 a to 2 c are attached to the elevator body 5 so that the buffer parts 2 a to 2 c first collide before the obstacle collides with the elevator body 5. Provided. In other words, the buffer portions 2a to 2c are provided so as to protrude from the elevator body 5 in the ascending direction A1 and the descending direction A2. In the present embodiment, a plurality of buffer units 2a to 2c are provided, and specifically, three buffer units are provided. The three buffer parts 2a to 2c are provided at both ends in the width direction of the elevator body 5 and at the lower part, respectively. The buffer portions 2a and 2b at both ends in the width direction have outer ends in the width direction including the end portions in the width direction of the chair 6 and protrude outward in the width direction from a virtual plane B perpendicular to the width direction. It is provided as follows. Since the buffer portions 2a and 2b at both ends in the width direction are provided in this way, when the elevator body 5 moves, before the obstacle collides with both ends in the width direction of the elevator body 5 and the chair 6, the buffer portion It can be made to collide with 2a, 2b. The lower buffer portion 2c is provided closer to the descending direction A2 of step 15. Specifically, the lower buffer portion 2c is a virtual plane C parallel to the ascending direction A1, the descending direction A2, and the horizontal direction, and is above the virtual plane C that does not intersect the stairs 3. Provided. This prevents the lower buffer portion 2c from being caught on the stairs 3 and preventing the elevator body 5 from moving. Even if a small object placed on the stairs 3 such as a small animal such as a cat or an infant becomes an obstacle, the lower buffer part 2c collides with the lower part of the elevator body 5, such as step 15. It can be made to collide with the buffer part 2c before doing. Since each buffer part 2a-2c has a softness | flexibility as mentioned above, even if it is a case where an obstacle collides with buffer part 2a-2c, the impact given to an obstacle is according to the softness | flexibility of buffer part 2a-2c. Since it functions as a cushion to be absorbed, damage to the obstacle can be minimized. Such buffer portions 2a to 2c may be detachably provided on the elevator body 5 or may be fixed by fastening means such as an adhesive and a bolt. By providing the buffer portions 2a to 2c in a detachable manner, for example, when there is a small animal or an infant in the environment used by the stair lift 1, the safety can be improved, and such buffer portions 2a to 2c are necessary. In an environment that is not, the space for the stair lift 1 can be saved by detaching the buffer portions 2a to 2c.

  FIG. 4 is a block diagram showing a simplified electrical configuration of the stair lift 1. The operation input unit 8 is a means for inputting operation command information of the elevator body 5 and is configured to be able to input, for example, a movement start operation and a stop operation. The operation input unit 8 is electrically connected to the control unit 9, and command information input by operation is given to the control unit 9. The operation input unit 8 is realized by, for example, a push button, and the movement direction is given to the control unit 9 when the user presses the button corresponding to the direction in which the user wants to move. The operation input unit 8 is provided in the armrest member 14 in the present embodiment.

  The sensor unit 7 includes a plurality of sensors 16 and 17 and a sensor control unit 18 that controls the sensors 16 and 17. The plurality of sensors 16, 17 are provided for detecting various types of information for controlling the stair elevator 1, and give the detected information to the sensor control unit 18. The sensor control unit 18 is electrically connected to the sensors 16 and 17, calculates information detected by the sensors 16 and 17 based on information given from the sensors 16 and 17, and calculates physical quantities such as speed and position. Ask for. The sensor control unit 18 gives information based on the calculated physical quantity to the control unit 9. In the present embodiment, as the sensors 16 and 17, there are a buffer sensor 17 provided in the buffer parts 2 a to 2 c and a seating sensor 16 provided in the chair 6. The buffer sensor 17 is a detection means, and detects a change in the shape of the buffer portions 2a to 2c. The seating sensor 16 is provided on the seat plate 12 on which the user is seated, and is a sensor for detecting whether or not the user is seated on the seat plate 12. The seating sensor 16 is realized by, for example, a pressure sensor that detects pressure.

  The control unit 9 is a control unit, and comprehensively controls each unit, for example, the sensor unit 7 and the driving device 10. The controller 9 is built in the elevator body 5. When an operation command is given from the operation input unit 8, the control unit 9 gives a drive command to the drive device 10 based on the given command. Further, the control unit 9 generates a drive command to be given to the drive device 10 based on the physical quantity detected by each of the sensors 16 and 17 given from the sensor control unit 18. When the pressure is not applied to the seat plate 12 based on the information provided from the seating sensor 16, in other words, when the object to be transported such as a user is not placed on the seat plate 12, the control unit 9 operates Even when an operation command is given from the input unit 8, control is performed so that the drive command is not given to the drive device 10. Therefore, even if the operation input unit 8 is operated in a state where the object to be conveyed is not placed on the seat plate 12, the elevator body 5 does not travel. As a result, the elevator body 5 can be prevented from traveling undesirably.

  Moreover, the control part 9 will control the drive device 10 so that the movement of the elevator main body 5 may be stopped, if the buffer sensor 17 detects the change of the shape of the buffer parts 2a-2c. Therefore, when the external force acts on the buffer portions 2a to 2c and the shape changes, the movement of the elevator body 5 is stopped. Moreover, the control part 9 became the original shape before the shape of buffer part 2a-2c changed in the stop period which the shape of buffer part 2a-2c changed and the movement of the elevator main body 5 is stopped. Is detected, the drive device 10 is controlled so as to continue the movement of the elevator body 5 again.

  FIG. 5 is a timing chart for explaining the operation of the control unit 9. FIG. 5A shows a waveform of a drive command given to the drive device 10 when there is no obstacle and the buffer sensor 17 does not operate. As shown in FIG. 5A, at time t1, the operation input unit 8 is operated from the state where the driving device 10 is stopped, and information for instructing an ascending or descending operation is given to the control unit 9. It is done. The controller 9 gives a drive command to the drive device 10 based on the given information, and raises or lowers the elevator body 5. When the arrival at the predetermined position at time t4 is given from another sensor to the control unit 9 via the sensor control unit 18, the control unit 9 gives a drive command to stop the operation. Therefore, the elevator main body 5 is movable across the upper floor and the lower floor when the user operates the operation input unit 8.

  FIGS. 5B and 5C show waveforms when there is an obstacle and the buffer sensor 17 detects the obstacle. FIG. 5B is a waveform of detection information detected by the buffer sensor 17, and FIG. 5C is a waveform of a drive command given to the drive device 10 by the control unit 9. As described above, at time t1, the operation input unit 8 is operated from the state where the driving device 10 is stopped, and information for instructing an ascending or descending operation is given to the control unit 9. The controller 9 gives a drive command to the drive device 10 based on the given information, and raises or lowers the elevator body 5. At time t <b> 2, the buffer sensor 17 detects a change in the shape of the buffer units 2 a to 2 c, and the detected information is given to the control unit 9 via the sensor control unit 18. Therefore, it can be seen that the buffer portions 2a to 2c are in contact with the obstacle at time t2. At time t3, the buffer sensor 17 detects that the shape of the buffer parts 2a to 2c has returned to the original shape before the change at time t2, so that the control unit 9 starts driving again. A drive command is given to the drive device 10. Thereafter, when the arrival at the predetermined position is given to the control unit 9 from another sensor via the sensor control unit 18 at time t5, the control unit 9 gives a drive command to stop the operation. Therefore, the control unit 9 can control to automatically stop driving of the driving device 10 when the obstacle is detected by the buffer sensor 17 and to start driving again when the obstacle is removed. .

  Further, when an obstacle is detected by the buffer sensor 17, it is preferable that the driving apparatus 10 is gradually decelerated and stopped without immediately stopping the driving apparatus 10. If the driving device 10 is immediately stopped, the inertial force generated upon a sudden stop is applied to the user sitting on the chair 6, and the user may be injured. In order to reduce such possibility as much as possible, it is preferable to decelerate according to the degree of deformation of the shape of the buffer portions 2a to 2c. Specifically, when the amount of deformation per unit time of the buffer portions 2a to 2c is large, the time until complete stop is shortened, and when the amount of deformation is small, the time is lengthened. Set. It is preferable that such a setting can be appropriately set according to the detection accuracy of the buffer sensor 17.

  When a plurality of buffer parts 2a to 2c are provided, only the deformation of the buffer parts 2a to 2c on the downstream side in the moving direction is detected by the buffer sensor 17, and the deformation of the other buffer parts 2a to 2c is ignored. Is preferred. As described above, by appropriately selecting the buffer portions 2a to 2c, the buffer sensor 17 can be controlled to be surely stopped by being deformed due to the obstacle. In addition, it is detected that the buffer sensor 17 has collided with the obstacle due to other causes not caused by the obstacle, for example, the user's hand touching the buffer portions 2a to 2c provided on the upstream side in the movement direction, which is undesirable. Stopping the driving device 10 can be prevented.

  Moreover, it is preferable that the control part 9 sets a threshold value beforehand based on the information given from the buffer sensor 17 so that the drive device 10 may not be stopped undesirably. The control unit 9 controls the drive device 10 to stop when the information given from the buffer sensor 17 is larger than a predetermined threshold value. Such a threshold value is set based on the detection accuracy of the buffer sensor 17 and is set to be larger than the noise that is constantly generated. For example, the threshold value is based on wind pressure generated when the elevator body 5 moves and microorganisms such as insects. It is set so that the detected information can be ignored.

  FIG. 6 is a cross-sectional perspective view showing the buffer portions 2a to 2c (hereinafter, the three buffer portions 2a to 2c may be collectively referred to as “buffer portion 2”). The buffer portion 2 includes a buffer material 19 having charging properties, a bag-like bag body 20 that covers the buffer material 19 from the outside, and two electrode portions 21 a and 21 b provided on the inner surface portion 20 a of the bag body 20. Including. The buffer portion 2 is configured such that the distance between the two electrode portions 21a and 21b changes when the shape is deformed. In addition, when the buffer portion 2 is filled with a buffer material between the two electrode portions 21a and 21b and the distance between the two electrode portions 21a and 21b changes, the capacitance between the two electrode portions 21a and 21b changes. Configured as follows.

  The bag body 20 is made of a flexible material such as cloth and can be easily deformed by an external force. The two electrode portions 21 a and 21 b have conductivity and are provided in the inner space of the bag body 20 so as to be separated from each other. Of the two electrode portions 21a and 21b, a region where one electrode portion 21a is provided is a detection region, and is provided in an inner portion of the region of the bag body 20 that comes into contact with the obstacle when it collides with the obstacle. One electrode part 21a has flexibility and is configured to be deformed in accordance with deformation of the bag body 20 when it collides with an obstacle. One electrode portion 21 a is configured, for example, in a flat plate shape, and is provided along the inner peripheral surface of the bag body 20. Accordingly, one surface portion in the thickness direction of one electrode portion 21a becomes a detection region for detecting an obstacle. The other electrode portion 21b is provided to be separated from the one electrode portion 21a and to face the one electrode portion 21a. A change in capacitance between the two electrode portions 21a and 21b is given to the sensor control unit 18 by a cable (not shown).

  The buffer material 19 is made of a material having charging properties. The buffer material 19 is made of, for example, a plastic material having excellent chargeability, and is specifically realized by a vinyl chloride resin, an acrylic resin, polyester, or the like. The buffer material 19 is filled at least between the two electrode portions 21a and 21b facing each other. The cushioning material 19 does not need to be filled in the entire inner space of the bag body 20, and changes in the distance between the two electrode portions 21 a and 21 b due to the deformation of the shape of the bag body 20. Any amount that can accumulate the necessary charge amount that can be detected may be used. Therefore, it is preferable that the inner space of the bag body 20 is filled with a cushioning material having cushioning properties to alleviate impact, such as cotton, in addition to the cushioning material 19. Such a buffer unit 2 functions as a so-called capacitance-type traveling sensor, and utilizes the fact that the capacitance changes in inverse proportion to the distance between the two electrode units 21a and 21b. A change in the distance between 21a and 21b is detected. Therefore, the deformation of the shape of the bag body 20 can be detected by detecting the capacitance between the two electrode portions 21a and 21b. Therefore, the buffer portion 2 changes its shape when it collides with an obstacle, and the shock at the time of the collision can be mitigated by the buffer material 19 and the cushion material which are inward of the bag body 20.

  The thickness dimension of the buffer part 2 is set to a dimension that can reduce damage to the obstacle when it collides with the obstacle and can detect deformation of the buffer part 2 with high accuracy, for example, 20 mm to 50 mm. The The flexibility of the buffer part 2 is not easily deformed by microorganisms such as insects and wind pressure received during movement, and when it collides with a small animal such as a cat or an infant, it is surely deformed and collides. It is preferable to select so as to absorb the impact generated during the process.

  As described above, in the stair lift 1 according to the present embodiment, the buffer bodies 2a to 2c having flexibility are provided on the elevator body 5 so as to protrude from the elevator body 5 in the ascending direction A1 and the descending direction A2. Therefore, when there is an obstacle in the moving path while the elevator body 5 is moving, if the buffer parts 2a to 2c collide with the obstacle, the buffer parts 2a to 2c have flexibility, so that damage to the obstacle is possible. Can be made smaller. Moreover, the control part 9 will control the drive device 10 so that the movement of the elevator main body 5 may be stopped, if the change of the shape of the buffer parts 2a-2c is detected by the buffer sensor 17. Therefore, when an obstacle collides with the buffer portions 2a to 2c, the shape of the flexible buffer portions 2a to 2c changes, this change is detected by the buffer sensor 17, and the movement of the elevator body 5 is stopped by the control unit 9. The Thus, even if it collides with an obstacle, the damage given to the obstacle can be made as small as possible, and the movement of the elevator body 5 can be automatically stopped. Thus, even if the obstacle is a person, the elevator body 5 can be stopped safely without causing injury to the person, and the safety of the stair elevator 1 can be improved.

  Further, in the buffer sensor 17 of the present embodiment, the region in which one of the electrode portions 21a of the buffer portions 2a to 2c is provided becomes the detection region. It is possible to reliably detect that the obstacle has collided. Thereby, the safety of the stair lift 1 can be improved.

  In the above-described embodiment, the buffer sensor 17 is realized by a so-called electrostatic capacitance type travel sensor, but is not limited thereto, and may be any sensor that can detect a change in the shape of the buffer units 2a to 2c. For example, as another sensor, a pressure sensor, a flow sensor, or a resistive touch panel may be used.

  Moreover, in the above-mentioned embodiment, although the guide rail 4 is being fixed to the staircase 3, it is not restricted to this, You may fix to the wall 3b which faces the slope or the staircase 3. FIG.

1 is a front view showing a stair lift 1 according to an embodiment of the present invention. 1 is a plan view showing a stair lift 1. It is a side view which shows the stair lift 1. It is a block diagram which simplifies and shows the electrical structure of the stair lift 1. 6 is a timing chart for explaining the operation of the control unit 9; 3 is a cross-sectional perspective view showing a buffer portion 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stair lift 2 Buffer part 3 Stair 4 Guide rail 5 Elevator body 6 Chair 8 Operation input part 9 Control part 10 Drive device 17 Buffer sensor 19 Buffer material 20 Bag body 21 Electrode part

Claims (2)

A transporter that travels along a guide rail installed on the stairs, ramps or walls facing the stairs of the building;
Drive means for driving the carrier along the guide rail;
Buffer means having flexibility, provided at both ends in the width direction of the carrier and at the lower part of the carrier so as to protrude from the carrier in the traveling direction of the carrier,
A detecting means provided in each of the buffering means for detecting a change in the shape of the buffering means;
Control means for controlling the drive means to stop the movement of the transporter when the change in the shape of the buffer means is detected by the detection means and the information given from the detection means is larger than a predetermined threshold value ; only including,
The control means detects the change in the shape of the buffer means downstream in the movement direction by the detection means provided in the buffer means downstream in the movement direction, and the movement direction is within the period in which the movement of the carrier is stopped. When the detecting means provided in the downstream buffer means detects that the shape of the buffer means downstream in the movement direction has returned to the shape before the change, the drive means is controlled to resume the movement of the transporter And
When the amount of deformation per unit time of the buffer means downstream in the movement direction is large, the control means shortens the time until the drive means completely stops, and the buffer means downstream of the movement direction An obstacle detection device for a stair lift , wherein when the amount of deformation per unit time is small, control is performed so as to increase the time until the drive means stops completely . The buffer means includes a buffer material having charging properties,
2. The obstacle detection device for a stair lift according to claim 1, wherein the detection means is a sensor that detects a capacitance that changes due to a change in shape of the buffer means.

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