Automatic cleaning device

Abstract

The utility model discloses an automatic cleaning device. The automatic cleaning device comprises wiping cloth; the mounting mechanism is used for mounting a to-be-cleaned part and can drive the to-be-cleaned part to move and / or rotate; the driving mechanism is used for driving the wiping cloth to be in contact with the to-be-cleaned part; the adsorption mechanism can be in contact with the wiping cloth; the cleaning medium supply mechanism is used for providing a cleaning medium for the adsorption mechanism, and the adsorption mechanism is used for providing the cleaning medium for the wiping cloth. The utility model discloses an automatic cleaning device to solve the problem of cleaning of an existing cylinder barrel.

Description

Technical Field

[0001] The present application relates to the technical field of processing equipment, and more specifically, to an automatic cleaning device. Background Art

[0002] After the cylinder is assembled, it needs to be bagged and packaged. Before bagging, the oil on the surface of the cylinder needs to be wiped to ensure the cleanliness of the cylinder. The operator needs to hold a wiping cloth and dip it in alcohol to wipe it. Manual wiping is labor-intensive and inefficient, and it will also cause problems such as uneven wiping and high cost of wiping cloth.

[0003] Therefore, an automatic cleaning device is needed to solve the above problems. Utility Model Content

[0004] In view of this, the purpose of the present application is to provide an automatic cleaning device to solve the existing cylinder cleaning problem.

[0005] Based on the above purpose, the present application provides an automatic cleaning device, comprising:

[0006] Wiping cloth;

[0007] A mounting mechanism, the mounting mechanism is used to mount the object to be cleaned and can drive the object to be cleaned to move and / or rotate;

[0008] A driving mechanism, the driving mechanism is used to drive the wiping cloth to contact the object to be cleaned;

[0009] an adsorption mechanism, the adsorption mechanism being capable of contacting the wiping cloth;

[0010] A cleaning medium supply mechanism is used to supply cleaning medium to the adsorption mechanism, and the adsorption mechanism is used to supply cleaning medium to the wiping cloth.

[0011] Optionally, the driving mechanism includes a power output structure and a release reel, a storage reel and a plurality of guide wheels respectively connected to the power output structure, and the plurality of guide wheels are arranged at intervals between the release reel and the storage reel; the power output structure can drive the release reel and / or the storage reel to rotate, so that the wiping cloth is output from the release reel, and after contacting the item to be cleaned, is recovered by the storage reel.

[0012] Optionally, the driving mechanism further comprises: a permanent magnetic clutch, the permanent magnetic clutch is connected to the release reel, and the permanent magnetic clutch is used to provide tensioning torque to the wiping cloth.

[0013] Optionally, the driving mechanism further includes: a pressure wheel and an encoder axially connected to the pressure wheel, the wiping cloth passes through the pressure wheel and drives the pressure wheel and the encoder to rotate, and the encoder can control the start and stop of the driving mechanism to control the feeding distance of the wiping cloth.

[0014] Optionally, the automatic cleaning device further comprises: a pressure mechanism, the pressure mechanism can reciprocate relative to the object to be cleaned, the pressure mechanism can at least partially wrap around the object to be cleaned, and the wiping cloth passes between the pressure mechanism and the object to be cleaned.

[0015] Optionally, the automatic cleaning device further comprises: the adsorption mechanism is arranged on a surface of the pressure mechanism facing the wiping cloth.

[0016] Optionally, the automatic cleaning device further comprises: two pressing mechanisms, which are respectively arranged on opposite sides of the object to be cleaned, and can reciprocate relative to the wiping cloth.

[0017] Optionally, the automatic cleaning device further comprises: an elastic tensioning mechanism, wherein the elastic tensioning mechanism is used to adjust the elastic deformation of the wiping cloth.

[0018] Optionally, the cleaning medium supply mechanism includes a tank body and a peristaltic pump, the cleaning medium is contained in the tank body, the tank body is connected to the peristaltic pump through a pipeline, and the peristaltic pump provides the cleaning medium to the adsorption mechanism through the pipeline.

[0019] In addition, optionally, the installation mechanism includes a clamping part, a moving part and a rotating part, the clamping part is used to extract the part to be cleaned, the moving part is connected to the clamping part, the moving part can drive the clamping part to move back and forth, and the rotating part is connected to the clamping part, and the rotating part can drive the clamping part to rotate back and forth.

[0020] From the above, it can be seen that the automatic cleaning device provided by the present application has the following advantages compared with the prior art: by using the above automatic cleaning device, the cleaning medium supply mechanism can provide the cleaning medium to the adsorption mechanism in real time, the adsorption mechanism provides the cleaning medium to the wiping cloth, and the wiping cloth soaked with the cleaning medium cleans the surface of the part to be cleaned on the installation mechanism, and the cleaning range can be fully covered. Moreover, the automatic cleaning device replaces manual labor, improves cleaning efficiency, and reduces the work intensity of workers. Moreover, the driving mechanism drives the wiping cloth to pass through the part to be cleaned at a uniform speed, which can achieve uniform wiping, ensure the wiping effect, and effectively use the wiping cloth to avoid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above-mentioned features and technical advantages of the present application will become clearer and easier to understand through the following description of its embodiments in conjunction with the accompanying drawings.

[0022] Figure 1 Schematic diagram of the automatic cleaning device used in the specific embodiment of the present application.

[0023] Figure 2 for Figure 1 A side view of the automatic cleaning device shown.

[0024] The reference numerals are:

[0025] 1. Release reel; 2. First clamping mechanism; 3. Elastic tensioning mechanism; 4. Pressing mechanism; 5. Storage reel; 6. Second clamping mechanism; 7. Tank body; 8. Peristaltic pump; 9. Sponge; 10. Encoder; 11. Permanent magnet clutch; 12. Installation mechanism; 13. Parts to be cleaned. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. The same parts are represented by the same figure numerals. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the accompanying drawings. The words "inside" and "outside" used refer to the direction toward or away from the geometric center of a specific component, respectively.

[0027] Figure 1 Schematic diagram of the automatic cleaning device used in the specific embodiment of the present application. Figure 2 for Figure 1 A side view of the automatic cleaning device shown in FIG. Figure 1 to Figure 2 As shown, the automatic cleaning device includes a wiping cloth, a mounting mechanism 12, a driving mechanism, an adsorption mechanism and a cleaning medium supply mechanism.

[0028] The wiping cloth can remove dust and dirt and can be used together with the cleaning medium. The wiping cloth is relatively soft and will not damage the surface of the object.

[0029] The mounting mechanism 12 is used to mount the part to be cleaned 13, and can drive the part to be cleaned 13 to move and / or rotate; if the wiping range of the wiping cloth can cover the surface of the part to be cleaned 13, the part to be cleaned 13 is arranged on the mounting mechanism 12, so that its surface faces the wiping cloth; if it is necessary to clean the part to be cleaned 13 in the circumferential direction, the part to be cleaned 13 is arranged on the mounting mechanism 12, and the mounting mechanism 12 needs to drive the part to be cleaned 13 to rotate back and forth; if it is necessary to clean the part to be cleaned 13 in the axial direction, the part to be cleaned 13 is arranged on the mounting mechanism 12, and the mounting mechanism 12 needs to drive the part to be cleaned 13 to move back and forth. The mounting mechanism 12 can also drive the part to be cleaned to move and rotate at the same time, that is, the part to be cleaned moves and rotates at the same time.

[0030] The driving mechanism is used to drive the wiping cloth to contact the object to be cleaned 13. When the driving mechanism drives the wiping cloth to pass through the object to be cleaned 13, the surface of the object is wiped and cleaned.

[0031] The adsorption mechanism can be in contact with the wiping cloth; when the adsorption mechanism is in contact with the wiping cloth, the adsorption mechanism can be arranged at a position before the wiping cloth contacts the object to be cleaned 13, or the adsorption mechanism and the object to be cleaned 13 are arranged relative to each other.

[0032] The cleaning medium supply mechanism is used to provide the cleaning medium to the adsorption mechanism, and the adsorption mechanism is used to provide the cleaning medium to the wiping cloth.

[0033] The workpiece 13 to be cleaned is set on the mounting mechanism 12, and the cleaning medium supply mechanism provides the cleaning medium to the adsorption mechanism. When the adsorption mechanism contacts the wiping cloth, the cleaning medium on the adsorption mechanism is transferred to the wiping cloth. The driving mechanism drives the wiping cloth to pass through the workpiece 13 to be cleaned, and the soaked wiping cloth can clean the surface of the workpiece 13 to be cleaned.

[0034] With the automatic cleaning device, the cleaning medium supply mechanism can provide the cleaning medium to the adsorption mechanism in real time, the adsorption mechanism provides the cleaning medium to the wiping cloth, and the wiping cloth soaked with the cleaning medium cleans the surface of the part to be cleaned 13 on the mounting mechanism 12, and the cleaning range can be fully covered. Moreover, the automatic cleaning device replaces manual labor, improves cleaning efficiency, and reduces the work intensity of workers. Moreover, the driving mechanism drives the wiping cloth to pass through the part to be cleaned 13 at a uniform speed, which can achieve uniform wiping, ensure the wiping effect, and effectively use the wiping cloth to avoid waste.

[0035] In order to achieve effective use of the wiping cloth, the driving mechanism optionally includes a power output structure and a release reel 1, a storage reel 5 and a plurality of guide wheels respectively connected to the power output structure, and the plurality of guide wheels are arranged at intervals between the release reel 1 and the storage reel 5; the power output structure can drive the release reel 1 and / or the storage reel 5 to rotate, so that the wiping cloth is output from the release reel 1, and after contacting with the object to be cleaned 13, it is recovered by the storage reel 5. The driving mechanism is mounted on a vertical plate, the release reel 1 is mounted on one end of the vertical plate, the storage reel 5 is mounted on the other end of the vertical plate, and the plurality of guide wheels are all mounted on the vertical plate, and are arranged at intervals between the release reel 1 and the storage reel 5. Usually, the release reel 1 and the storage reel 5 are arranged at the relatively upper ends of the vertical plate, and the object to be cleaned 13 is arranged at the relatively lower part of the vertical plate. Therefore, the guide wheels guide the wiping cloth released by the release reel 1 from top to bottom to the vicinity of the object to be cleaned 13, and then guide the wiping cloth from bottom to top into the storage reel 5. When in use, the wiping cloth is in a rolled shape and is set on the release reel 1. The other end of the wiping cloth is connected to the storage reel 5. When the power output structure drives the storage reel 5 to rotate, the release reel 1 is driven to rotate to output the wiping cloth. The wiping cloth passes through each guide wheel in turn, and cleans the surface of the object to be cleaned 13 when passing through it. The storage reel 5 stores the used wiping cloth.

[0036] In one embodiment of the present application, a guide wheel is provided at each opposite end of the item to be cleaned 13, and is symmetrically arranged along the item to be cleaned 13; two guide wheels are provided between the guide wheel on the left side of the item to be cleaned 13 and the storage reel 5, and three guide wheels are provided between the guide wheel on the right side of the item to be cleaned 13 and the release reel 1.

[0037] In order to ensure that the wiping cloth can be effectively cleaned, the driving mechanism may further include: a permanent magnetic clutch 11, which is connected to the release reel 1 and is used to provide tension torque to the wiping cloth. The power output structure outputs driving force to control the rotation of the storage reel 5, driving the release reel 1 connected by the permanent magnetic clutch 11 to rotate, and the permanent magnetic clutch 11 keeps the wiping cloth between the release reel 1 and the storage reel 5 under tension to prevent the wiping cloth from falling off.

[0038] Optionally, the driving mechanism also includes: a pressure wheel and an encoder 10 axially connected to the pressure wheel. The wiping cloth passes through the pressure wheel and drives the pressure wheel and the encoder 10 to rotate. The encoder 10 can control the start and stop of the driving mechanism to control the feeding distance of the wiping cloth. The pressure wheel is provided with a rotating shaft. The encoder 10 is fixedly connected to the rotating shaft of the pressure wheel. When the wiping cloth passes through the pressure wheel, the pressure wheel is driven to rotate synchronously when the wiping cloth is transmitted. The encoder 10 synchronously follows the rotation of the pressure wheel to accurately feedback the feeding distance of the wiping cloth in real time. When the feeding distance reaches the set value, the encoder 10 feeds back a signal to the driving mechanism to stop feeding. By adopting the above-mentioned driving mechanism, the feeding distance of the wiping cloth can be accurately controlled to avoid wasting the wiping cloth.

[0039] In one embodiment of the present application, the encoder 10 is capable of measuring the moving distance of the wiping cloth. The encoder 10 and the guide wheel press the wiping cloth at an angle to facilitate accurate reading and avoid waste of the wiping cloth.

[0040] In order to avoid the failure of the wiping cloth to contact the surface of the object to be cleaned 13, optionally, the automatic cleaning device further includes: a pressure mechanism 4, which can reciprocate relative to the object to be cleaned 13, and the pressure mechanism 4 can at least partially wrap around the outside of the object to be cleaned 13, and the wiping cloth passes between the pressure mechanism 4 and the object to be cleaned 13. The pressure mechanism 4 is arranged relatively above the object to be cleaned 13 and can reciprocate relative to the object to be cleaned 13. When the pressure mechanism 4 approaches the object to be cleaned 13, such as the pressure mechanism 4 half wraps around the object to be cleaned 13, the wiping cloth is pressed against the surface of the object to be cleaned 13, the contact area between the two is increased, and effective wiping is ensured.

[0041] In one embodiment of the present application, the pressure mechanism 4 includes a pressure portion and a driving portion. The driving portion is disposed on the vertical plate, is connected to the pressure portion, and drives the pressure portion to reciprocate.

[0042] In order to facilitate the adsorption mechanism to provide the cleaning medium in time, optionally, the automatic cleaning device further includes: the adsorption mechanism is arranged on the surface of the pressure mechanism 4 facing the wiping cloth. When the pressure part moves downward, the adsorption mechanism abuts against the wiping cloth, and when the adsorption mechanism is squeezed, the cleaning medium inside is released onto the wiping cloth, and the wiping cloth absorbs the cleaning medium in time to effectively clean the surface of the object to be cleaned 13.

[0043] In one embodiment of the present application, the adsorption mechanism includes but is not limited to a sponge 9 , and a pipe connected to a peristaltic pump 8 is provided on the inner surface of the pressure-applying portion, and the pipe is used to provide a cleaning medium to the sponge 9 .

[0044] In one embodiment of the present application, two avoidance grooves are provided on the inner surface of the pressure-applying portion, and the two avoidance grooves are symmetrically arranged along the sponge 9, and the wiping cloth passes from under the two guide wheels and over the part to be cleaned 13; when the pressure-applying portion moves toward the side of the part to be cleaned 13, the guide wheel enters the avoidance groove, the sponge 9 abuts against the wiping cloth, and the wiping cloth abuts against the part to be cleaned 13.

[0045] Optionally, the automatic cleaning device further includes: two clamping mechanisms, which are respectively arranged on opposite sides of the part to be cleaned 13, and the clamping mechanisms can reciprocate relative to the wiping cloth. When the clamping mechanism is close to the wiping cloth, it can apply pressure to the wiping cloth. When the wiping cloth is fed, the clamping mechanism moves away from the wiping cloth, and when the pressure mechanism 4 acts on the wiping cloth, the two clamping mechanisms act on the wiping cloth at the same time, so that the wiping cloths on opposite sides of the part to be cleaned 13 have tensioning force. The clamping mechanism can prevent the pressure mechanism from pulling the release reel 1 and / or the storage reel 5 when pressing the wiping cloth to wipe the surface of the cylinder, thereby preventing the wiping cloth from slipping and affecting the cleaning effect.

[0046] In one embodiment of the present application, the clamping mechanism includes a clamping portion and a driving portion, wherein the driving portion is disposed on the vertical plate, is connected to the clamping portion, and drives the clamping portion to reciprocate.

[0047] In one embodiment of the present application, one clamping mechanism is disposed near the release reel 1 , which is the first clamping mechanism 2 , and another clamping mechanism is disposed near the storage reel 5 , which is the second clamping mechanism 6 .

[0048] Optionally, the automatic cleaning device further comprises: an elastic tensioning mechanism 3, which is used to adjust the elastic deformation of the wiping cloth. The elastic tensioning mechanism is used to tighten the wiping cloth, and the deformation of the wiping cloth pressed down by the pressure mechanism 4 is provided by the elastic tensioning mechanism 3, and the deformation is used to prevent the wiping cloth from being torn.

[0049] Optionally, the cleaning medium supply mechanism includes a tank body 7 and a peristaltic pump 8. The cleaning medium is contained in the tank body 7. The tank body 7 is connected to the peristaltic pump 8 through a pipeline. The peristaltic pump 8 provides the cleaning medium to the adsorption mechanism through the pipeline. The cleaning medium is stored in the tank body 7. When the peristaltic pump 8 is started, the peristaltic pump 8 extracts the cleaning medium from the tank body 7 and provides it to the adsorption mechanism. The adsorption mechanism adsorbs the cleaning medium. When the adsorption mechanism is squeezed, the adsorption mechanism releases the cleaning medium onto the wiping cloth. By adopting the above-mentioned cleaning medium supply mechanism, the cleaning medium can be provided to the wiping cloth in real time to ensure the cleaning effect of the wiping cloth.

[0050] The cleaning medium is selected for the type of stains on the outer surface of the cylinder barrel. In one embodiment of the present application, the cleaning medium includes but is not limited to alcohol.

[0051] In addition, optionally, the mounting mechanism 12 includes a clamping part, a moving part and a rotating part. The clamping part is used to extract the part to be cleaned 13. The moving part is connected to the clamping part, and the moving part can drive the clamping part to move back and forth. The rotating part is connected to the clamping part, and the rotating part can drive the clamping part to rotate back and forth. The clamping part is used to extract the cylinder barrel. The moving part can drive the clamping part to move back and forth. The clamping part carries the cylinder barrel to move back and forth synchronously, so that the wiping cloth can fully cover the cylinder barrel in the axial direction. The rotating part can drive the clamping part to rotate back and forth. The clamping part carries the cylinder barrel to rotate back and forth synchronously, so that the wiping cloth can fully cover the cylinder barrel in the circumferential direction. The moving part and the rotating part can drive the clamping part simultaneously or separately. For example, after the clamping part picks up the cylinder barrel, the moving part and the rotating part drive the clamping part simultaneously, that is, the clamping part drives the cylinder barrel to move and rotate at the same time, thereby increasing the wiping speed. By adopting the above-mentioned installation mechanism 12, the clamping part can be used in conjunction with cylinders or other cylinders, elongated bodies, and rectangular blocks of different diameters, and the wiping range can fully cover the outer surface of the cylinder to avoid blind spots.

[0052] In one embodiment of the present application, the clamping portion includes but is not limited to a clamping claw and a clamping plate. Usually, the clamping portion includes two clamping plates arranged opposite to each other, and the clamping plates are respectively abutted against opposite ends of the cylinder.

[0053] The following further describes the use of the automatic cleaning device.

[0054] A whole roll of wiping cloth is installed on the release reel 1, and one end of the wiping cloth is fixed on the storage reel 5 after passing through each guide wheel in turn. The power output structure drives the storage reel 5 to rotate, and drives the release reel 1 to rotate to realize the transmission of the wiping cloth. The permanent magnet clutch 11 acts on the release reel 1, and provides a tightening torque through the permanent magnet clutch 11 to prevent the whole roll of wiping cloth from scattering.

[0055] The tank 7 is filled with a cleaning medium, which is quantitatively transported to the adsorption mechanism by a peristaltic pump 8. The part to be cleaned 13 is installed on the installation mechanism 12 manually or by a loading robot. During wiping, the pressure mechanism 4 presses down the adsorption mechanism, and the adsorption mechanism releases the cleaning medium onto the wiping cloth; at the same time, the wiping cloth is pressed down, so that the wiping cloth soaked with the cleaning medium is half-wrapped on the surface of the part to be cleaned 13. The installation mechanism 12 drives the part to be cleaned 13 to move and rotate, so that the wiping cloth can clean the stains on the surface of the part to be cleaned 13. To prevent the wiping cloth from slipping, two clamping mechanisms clamp the wiping cloth. When wiping is completed, the two clamping mechanisms are lifted when the wiping cloth is fed. When the pressure mechanism 4 is pressed down, the elastic tensioning mechanism 3 provides the tensile deformation of the wiping cloth; the wiping cloth that has completed cleaning is recovered by the storage reel 5, and the encoder 10 feedbacks the feeding distance in real time. After reaching the set value, it stops rotating, and the two clamping mechanisms clamp and fix the wiping cloth.

[0056] From the above description and practice, it can be seen that the automatic cleaning device provided by the present application has the following advantages compared with the prior art: by using the above automatic cleaning device, the cleaning medium supply mechanism can provide the cleaning medium to the adsorption mechanism in real time, the adsorption mechanism provides the cleaning medium to the wiping cloth, and the wiping cloth soaked with the cleaning medium cleans the surface of the part to be cleaned on the installation mechanism, and the cleaning range can be fully covered. Moreover, the automatic cleaning device replaces manual labor, improves cleaning efficiency, and reduces the work intensity of workers. Moreover, the driving mechanism drives the wiping cloth to pass through the part to be cleaned at a uniform speed, which can achieve uniform wiping, ensure the wiping effect, and effectively use the wiping cloth to avoid waste.

[0057] A person skilled in the art should understand that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the scope of the present application should be included in the protection scope of the present application.

Claims

1. An automatic cleaning device, characterized in that: include: Wiping cloth; A mounting mechanism, the mounting mechanism is used to mount the object to be cleaned and can drive the object to be cleaned to move and / or rotate; A driving mechanism, the driving mechanism is used to drive the wiping cloth to contact the object to be cleaned; an adsorption mechanism, the adsorption mechanism being capable of contacting the wiping cloth; A cleaning medium supply mechanism is used to supply cleaning medium to the adsorption mechanism, and the adsorption mechanism is used to supply cleaning medium to the wiping cloth.

2. The automatic cleaning device according to claim 1, characterized in that: The driving mechanism comprises a power output structure, and a release reel, a storage reel and a plurality of guide wheels respectively connected to the power output structure, wherein the plurality of guide wheels are arranged at intervals between the release reel and the storage reel; The power output structure can drive the release reel and / or the storage reel to rotate, so that the wiping cloth is output from the release reel, and after coming into contact with the object to be cleaned, is recovered by the storage reel.

3. The automatic cleaning device according to claim 2, characterized in that: The driving mechanism further comprises: a permanent magnetic clutch connected to the release reel, and the permanent magnetic clutch is used to provide tensioning torque to the wiping cloth.

4. The automatic cleaning device according to claim 2 or 3, characterized in that: The driving mechanism also includes: a clamping wheel and an encoder axially connected to the clamping wheel. The wiping cloth passes through the clamping wheel and drives the clamping wheel and the encoder to rotate. The encoder can control the start and stop of the driving mechanism to control the feeding distance of the wiping cloth.

5. The automatic cleaning device according to any one of claims 1 to 3, characterized in that: Also includes: A pressure mechanism, wherein the pressure mechanism can reciprocate relative to the object to be cleaned, the pressure mechanism can at least partially wrap around the object to be cleaned, and the wiping cloth passes between the pressure mechanism and the object to be cleaned.

6. The automatic cleaning device according to claim 5, characterized in that: Also includes: The adsorption mechanism is arranged on a surface of the pressure mechanism facing the wiping cloth.

7. The automatic cleaning device according to claim 5, characterized in that: Also includes: Two clamping mechanisms are respectively arranged on opposite sides of the object to be cleaned, and the clamping mechanisms can reciprocate relative to the wiping cloth.

8. The automatic cleaning device according to claim 6, characterized in that: Also includes: An elastic tensioning mechanism is used to adjust the elastic deformation of the wiping cloth.

9. The automatic cleaning device according to any one of claims 1 to 3, characterized in that: The cleaning medium supply mechanism comprises a tank body and a peristaltic pump. The cleaning medium is contained in the tank body. The tank body is connected to the peristaltic pump through a pipeline. The peristaltic pump provides the cleaning medium to the adsorption mechanism through the pipeline.

10. The automatic cleaning device according to any one of claims 1 to 3, characterized in that: The installation mechanism includes a clamping part, a moving part and a rotating part. The clamping part is used to extract the items to be cleaned. The moving part is connected to the clamping part, and the moving part can drive the clamping part to move back and forth. The rotating part is connected to the clamping part, and the rotating part can drive the clamping part to rotate back and forth.

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