def to_xml(self, xml_parent):
    joint = SubElement(xml_parent, 'joint')
    joint.set('name', self.name)
    joint.set('type', self.type)
    self.parent_link.to_xml(joint)
    self.child_link.to_xml(joint)
    self.origin.to_xml(joint)
    self.axis.to_xml(joint)
    self.limit.to_xml(joint)
    return joint
def to_xml(self, xml_parent):
    joint = SubElement(xml_parent, 'joint')
    joint.set('name', self.name)
    joint.set('type', self.type)
    self.parent_link.to_xml(joint)
    self.child_link.to_xml(joint)
    self.origin.to_xml(joint)
    self.axis.to_xml(joint)
    self.limit.to_xml(joint)
    return joint