1. Field of the Invention
The present invention relates to a rolling element accommodating belt, a linear guide apparatus and a metallic mold for manufacturing the rolling element accommodating belt.
2. Description of Related Art
In the linear guide apparatus, a slider is relatively moved with respect to a guide rail through a plurality of rolling elements which are rolling and circulating in an infinite circulating passage. However, in the linear guide apparatus, while the slider is relatively moving with respect to the guide rail, the rolling elements are rolling and moved in the same direction. Therefore, the rolling elements, which are adjacent to each other, are rubbed to each other. Accordingly, the rolling elements can not be smoothly rolled. Therefore, an intensity of noise is increased and abrasion of the rolling elements is facilitated. In order to solve the above problems by suppressing the generation of noise and making the linear guide apparatus operated smoothly, a rolling element accommodating belt is conventionally proposed in which the rolling elements are aligned in the alignment direction in the infinite circulating passage so as to smoothly operate the linear guide apparatus. Concerning this rolling element accommodating belt, for example, refer to Japanese Patent Unexamined Publications JP-A-05-52217, JP-A-2001-165169, JP-A-10-9264, JP-A-09-14264, JP-A-11-247856 and JP-A-2005-69444.
For example, according to the JP-A-05-52217, JP-A-2001-165169 and JP-A-10-9264, a rolling element accommodating belt is disclosed which includes spacer portions interposed between the rolling elements adjacent to each other and also includes connecting arm portions for connecting the spacer portions. According to the rolling element accommodating belt composed as described above, the rolling elements are aligned in a line in the alignment direction in the infinite circulating passage so as to suppress the generation of noise so that the rolling elements can be smoothly circulated in the infinite circulating passage. In this connection, according to the technique described in the JP-A-2001-165169, the rolling element accommodating belt is composed in such a manner that the rolling elements accommodated on the rolling element accommodating belt can be freely detached in a perpendicular direction to the front and the back surface of the rolling element accommodating belt.
This type rolling element accommodating belt is obtained when melted resin material is poured from a gate into a product configuration portion in a metallic mold. However, in the product configuration portion in the metallic mold, residual air and gas, which is generated from the melted resin material, exists. These gases tend to stay in a portion where a gas flowing passage comes to a dead end. Especially, these gases tend to stay in an end portion of the above spacer portion. Therefore, it is difficult for the melted resin to smoothly flow into this portion where the gases are staying. Accordingly, an underfill portion of resin (which is a portion where predetermined amount of resin is not filled) is generated on the rolling element accommodating belt formed in the mold. When the underfill portion of resin is generated in this way, there is a possibility that damage starts from this underfill portion of resin generated on the rolling element accommodating belt.
In this case, for example, according to the technique described in the JP-A-11-247856 or JP-A-2005-69444, a joint portion of the upper mold and the lower mold of the metallic mold can be made to function as a gas vent. However, at the end portion of the formed spacer portion, no means is provided for discharging gas. Therefore, gas tends to stay at the end portion of the formed spacer portion. Therefore, the spacer portion needs to be more investigated to discharge gas so that the generation of an under fill portion of resin can be prevented.
Further, concerning the method of manufacturing this type rolling element accommodating belt, for example, the JP-A-05-52217 discloses a technique in which the rolling elements are arranged in a metallic mold so that the rolling elements can be used as a core and then injection molding is conducted to manufacture the rolling element accommodating belt.
The JP-A-09-14264 discloses a technique in which injection molding is conducted while the rolling elements are being used as a core in the same manner as that described above. However, in order to solve a problem that a portion, in which the rolling elements are accommodated, and the rolling elements are tightly contacted with each other by the shrinkage caused at the time of forming, oil or water is absorbed after the completion of molding.
Another manufacturing method is disclosed in the JP-A-11-247856 as follows. For example, in the JP-A-11-247856, rolling element shaped-molds, the sizes of which are larger than the diameters of the rolling elements to be used, are arranged at predetermined intervals and injection molding is conducted to manufacture a rolling element accommodating belt.
The JP-A-2005-69444 discloses a technique in which a formed rolling element accommodating belt is detached from a metallic mold by obliquely moving the metallic mold used in the injection molding. In this case, in the examples disclosed in the JP-A-11-247856 and JP-A-2005-69444, a position of a dividing line of an upper mold and a lower mold is located at a peripheral portion of a spacer portion. Concerning this matter, refer to FIG. 2 of the JP-A-11-247856 and FIG. 9 of JP-A-2005-69444.
However, in the above method of manufacturing the rolling element accommodating belt, for example, in the technique described in the JP-A-05-52217 in which injection molding is conducted while the rolling elements are being used as a core, due to the shrinkage of material caused at the time of forming, sizes of portions, in which the rolling elements are accommodated, are reduced smaller than the predetermined sizes. Therefore, the rolling elements can not be smoothly rolled.
For example, in the technique described in the JP-A-09-14264, in order to avoid a case where the rolling elements can not be smoothly rolled because of the shrinkage caused at the time of forming, the processing of absorbing oil or the processing of absorbing water is conducted after the completion of forming. In this case, it is necessary to strictly control the conditions of processing of absorbing oil or absorbing water, which raises the manufacturing cost.
For example, in the technique described in the JP-A-11-247856, in the spacer portion which has been formed, a concave face corresponding to the circumferential face of the rolling element mold is formed as an under-cut portion. Therefore, when the rolling element belt is detached from the metallic mold, a strong force is given to the rolling element accommodating belt. Accordingly, there is a possibility that the rolling element accommodating belt is damaged or deformed.
Further, in the technique described in the JP-A-11-247856 and the JP-A-2005-69444, a position of the dividing line of the upper and the lower mold of the metallic mold is located in the peripheral portion of the spacer portion. Accordingly, burr is generated in the peripheral portion of the spacer portion. Due to the generation of burr, there is a possibility that the linear guide apparatus can not be smoothly operated. That is, at the time of forming, resin flows into a joint portion of the upper mold and the lower mold, which causes the generation of burr. In the case where this burr is generated in the peripheral portion of the spacer portion, when the rolling element accommodating belt circulates in the infinite circulating passage of the linear guide apparatus, the rolling element accommodating belt rubs an inner circumferential wall of the infinite circulating passage. Alternatively, the rolling element accommodating belt is hooked on the inner circumferential wall of the infinite circulating passage. Therefore, there is a possibility that a smooth operation of the linear guide apparatus is obstructed.
In the case of the rolling element accommodating belt disclosed in JP-A-2001-165169, the rolling elements accommodated there can be freely detached in a direction perpendicular to the surface side and the back side of the rolling element accommodating belt. For example, as exemplarily shown in FIG. 17, a position of the dividing line of the metallic mold of the spacer portion is formed while crossing a face including a portion coming into contact with the rolling elements. When the dividing line of the metallic mold is set at this position, burr is not generated in the periphery of the spacer portion, however, burr is generated in a portion coming into contact with the rolling elements. Therefore, by the burr protruding onto the rolling element side, the face, which is to be contacted with the rolling elements, and the rolling elements can not be stably contacted with each other. Accordingly, smooth operation of the linear guide apparatus is obstructed. In order to prevent the above generation of burr, it is necessary to enhance the accuracy of the joint face of the metallic mold. Alternatively, it is necessary to severely control the forming condition. However, when the above countermeasures are taken, the manufacturing cost is raised.