Q.
hough_lines_dir の circle版のような処理サンプルございませんでしょうか？

A.
下記の通り作成いたしましたので、ご確認いただけましたら幸いです

dev_update_off ()
read_image (Image, '/rings/washers_01.png')
radius:=50
threshold (Image, Region, 0, 128)

opening_circle (Region, RegionOpening, 5)
connection (RegionOpening, ConnectedRegions)
select_shape (ConnectedRegions, SelectedRegions, 'area', 'and', 5000, 6500)
count_obj (SelectedRegions, Number)
dev_set_draw ('margin')
dev_set_line_width (5)
for Index := 1 to Number by 1
    select_obj (SelectedRegions, ObjectSelected, Index)
    hough_circles (ObjectSelected, RegionOut, radius, 40, 0)   
    area_center (RegionOut, Area, Row, Column)
    gen_circle (Circle, Row, Column, radius)
    dev_set_color ('red')
    dev_display (Image)
    dev_display (Circle)
    dev_disp_text ('hough_circlesを用いた円検出', 'window', 0, 0, 'black', [], [])
    stop ()
    hough_circle_trans (ObjectSelected, HoughImage, radius)
    scale_image_max (HoughImage, ImageScaleMax)
    threshold (ImageScaleMax, MaxRegion, 255, 255)
    area_center (MaxRegion, Area1, Row1, Column1)
    gen_circle (Circle1, Row1-radius, Column1-radius, radius)
    dev_set_color ('green')
    dev_display (Image)
    dev_display (Circle1)
    dev_disp_text ('hough_circle_transを用いた円検出', 'window', 0, 0, 'black', [], [])
    stop ()
endfor